plaster

updated mon 26 mar 12

Ron Roy on wed 27 mar 96

Hello the list,

Does anyone know if old plaster (powder) can be made good again by
calcining? If so what temperature?

Thanks, RR

Louis Howard Katz on thu 28 mar 96

You can recalcine plaster by putting it in an oven at about 350 degrees
for a few hours. This turns the gypsum into plaster of Paris, but it will
may not revert any hardeners or modifiers that have been added to the
plaster. The plaster may need to be lightly ground to be usable.
Louis
P.S. I tried this on a small amount of plaster years ago, it worked O.K..
The information came from the mold instructor at P.C.A. named Petrus. I
don't know his last name.


***************************************************
*Louis Katz lkatz@falcon.tamucc.edu *
*Texas A&M University Corpus Christi *
*6300 Ocean Drive, Art Department *
*Corpus Christi, Tx 78412 *
*Phone (512) 994-5987 *
**************************************************

ktighe on mon 22 jul 96

Regarding plaster--- I make plaster molds for original sculpture and spent
far too much energy in the past seeking out perfect plaster. Two hours by
car from my home is a place where I would spend $20 for #1 Casting plaster,
available only in 100 lb. bags. Then I discovered a place only one hour
away that carried #1 Pottery plaster for about $10 in 50lb. bags. I would
have to arrange these purchases around trips into the city etc. I would
over-buy, and end up with plaster I couldn't use, because all plaster has a
shelf life and must be stored carefully. Now, in a paint supply store that
is stone's throw from my house, I buy Drywall Brand Plaster of Paris in 25
lb. bags for $4.50. It is an excellent product, produces a very hard mold,
and I can't believe all the time and energy I spent worrying about the
perfect plaster. Put me in the electric-chair purists; but plaster is
plaster is freaking plaster.--- Kenneth

Jonathan Kaplan on mon 22 jul 96

>----------------------------Original message----------------------------
>Regarding plaster--- I make plaster molds for original sculpture and spent
>far too much energy in the past seeking out perfect plaster. Two hours by
>car from my home is a place where I would spend $20 for #1 Casting plaster,
>available only in 100 lb. bags. Then I discovered a place only one hour
>away that carried #1 Pottery plaster for about $10 in 50lb. bags. I would
>have to arrange these purchases around trips into the city etc. I would
>over-buy, and end up with plaster I couldn't use, because all plaster has a
>shelf life and must be stored carefully. Now, in a paint supply store that
>is stone's throw from my house, I buy Drywall Brand Plaster of Paris in 25
>lb. bags for $4.50. It is an excellent product, produces a very hard mold,
>and I can't believe all the time and energy I spent worrying about the
>perfect plaster. Put me in the electric-chair purists; but plaster is
>plaster is freaking plaster.--- Kenneth

While I might, in very broad general non specific terms agree that plaster
is plaster is freaking plaster, or chemically speaking, they partial
hydration of a gypsum product, or the change in alpha gypsum to beta
gypsum, whatever, I would none the less disagree with you and state that
plaster is not palster is not freaking plaster.

While I share your travel concerns, it does a great dis-service to put
forward mis-information to this list. While it may work for you, and I am
pleased that you found this solution, I would never trust any product for
use in my shop that I didn't know diddly squat about, especially plaster.

There may be no perfect plaster for your particular application (but I
doubt this). But there are plasters, gypsum cements, that are superior in
formulation and use for specific applications. In fact, a very significant
portion of the ceramic industry uses industrial plaster for the resuklting
clay work, and my bet is that indeed, there are specific applications for
specific plasters. Go ahead, make some casting molds from Ceramical or
Ultracal 30 and then post your results to the list. I'm willing to bet that
your statement of plaster beign plaster being freaking plaster will be gone
by then.

Please get your information correct before making such bold assertions.

Jonathan



Jonathan Kaplan
Ceramic Design GroupLtd./Production Services
PO Box 775112
Steamboat Springs CO 80477
(970) 879-9139 voice and fax
call before faxing

"Show up, pay attention, tell the truth, don't be attatched to the results!"

Russel Fouts on thu 25 jul 96

PlasterCasters,

I've just made my first plaster mold (no great shakes, just a hump mold) and
read that it should now dry for TWO to THREE WEEKS before using it!?

Awww come on, can't I speed that up some?

Is it that it takes that long to dry out or are some chemical reactions still
taking place and hurrying it would make a weaker mold?

This will be the master for the working molds.

Russel ("Arthur Murry, taught me plaster in a hurry......")



=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
* Russel Fouts, CI$: 100021,23,
Bruxelles, Belgium
Internet: 100021.23@CompuServe.Com

"It took more then one man to change my name to Shanghai Lil."
MD
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-


!^NavFont01F0007NGHHH6A7DC6

Lori Wilkinson on thu 25 jul 96

At 09:16 AM 7/25/96 EDT, you wrote:
>----------------------------Original message----------------------------
>
> PlasterCasters,
>
> I've just made my first plaster mold (no great shakes, just a hump mold) and
>read that it should now dry for TWO to THREE WEEKS before using it!?
>
> Awww come on, can't I speed that up some?
>
Russel,

My experience has been that I have been able to use the mold as soon as it
felt dry to the touch and here in New Mexico drying it on a rack it took
less than a week. I am talking about a larger hump mold that I made 18"
platters with.

Lori Wilkinson Roswell NM

Jonathan Kaplan on tue 25 jul 00

I have always wondered why so many potters have such a fear of plaster in
the studio. I know it stems from a lack of education. Or from being
mis-informed or poorly educated.

There is a wonderful relationship between plaster and clay, and clay and
plaster. Having worked with this relationship for a long time I have come
to have a respect for both materials and their unlimited potentials.

Just as a side bar, the fear that many have of getting chunks of plaster in
their clay from a plaster wedging table surface surfaces many times on this
list and never ceases to amaze me. If the table is built correctrly and the
plaster mixed and poured correctly, there is really no problem. And yes, a
chunk of plaster in your pot will cause the section of the pot to blow off
due to the hydroscopic nature of plaster as well as to its expansion when
the pot is fired. However, an old slip casting/mold making trick in
adjusting for proper viscosity and specific gravity is too add a small
amount of powdered plaster to the slip mix. The resulting adjusted mix
never has been problematic in our shop on the times wse have needed to use
this method.

Plaster is one of those underused, underestimated and over feared materials
that is of such benefit to potters, often maligned because of mis-education
and mis-information.

Jonathan

Jonathan Kaplan, president
Ceramic Design Group
PO Box 775112
Steamboat Springs CO 80477
voice and fax 970 879-9139
jonathan@csn,net
http://www.sni.net/ceramicdesigin

Plant Location:
1280 13th Street Unit 13
Steamboat Springs CO 80487
(please use this address for all deliveries via UPS, comman carrier, FEd
Ex, etc.)

Tommy Humphries on tue 25 jul 00

Down here at Marshall Pottery, back in the days before the helpers got lazy
and we started using clay straight from the pug, ALL the potters clay was
wedged and rolled on plaster benches. This was upwards of 2-4 TONS of clay a
day without any problems of plaster getting into the clay. Of course we
used the plaster ball benches wet, to keep the clay from sticking, and I
think that this helped to cut down the chipping. Over the course of a years
time an 8" thick bench would have a pair of 6" deep depressions worn into
the surface from clay contact. Back in the "good ol days" all the potters
clay was pounded across a wire a minimum of 12 times to remove the air.

I also have wondered why so many were opposed to plaster, and why those who
weren't used it dry...

Tommy Humphries,

"`You know, it's at times like this, that I really wish I'd listened to what
my mother told me when I was young.'
`Why, what did she tell you?'
`I don't know, I didn't listen.'"
(Douglas Adams)

----- Original Message -----
From: "Jonathan Kaplan"
To:
Sent: Tuesday, July 25, 2000 8:03 AM
Subject: Plaster


> I have always wondered why so many potters have such a fear of plaster in
> the studio. I know it stems from a lack of education. Or from being
> mis-informed or poorly educated.
>
> Jonathan
>
> Jonathan Kaplan, president
> Ceramic Design Group
> PO Box 775112
> Steamboat Springs CO 80477
> voice and fax 970 879-9139
> jonathan@csn,net
> http://www.sni.net/ceramicdesigin
>
> Plant Location:
> 1280 13th Street Unit 13
> Steamboat Springs CO 80487
> (please use this address for all deliveries via UPS, comman carrier, FEd
> Ex, etc.)
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
>

David Hendley on wed 26 jul 00

I have to agree with Jonathon here. Plaster goes with clay
like, as our hometown boy Neil McCoy sings, coffee with a cup.
Yes, if you get a chunk of plaster in your clay it will cause
a blowout after firing.
You don't get plaster in your clay. You cover your wedging
table with canvas and you treat batts with care. You really
have to be pretty rough to break off chunks.

Not using plaster out of fear is like not using a gas kiln
out of fear. Sure, you can use an electric kiln all your life,
but you are severely limiting yourself. Nothing's better
than plaster for drying out clay, and it's also great for
press molds and sprigging. And of course making full
blown molds is an art in itself.
--
David Hendley
Maydelle, Texas
hendley@tyler.net
http://www.farmpots.com/





----- Original Message -----
From: Jonathan Kaplan
To:
Sent: Tuesday, July 25, 2000 8:03 AM
Subject: Plaster


| I have always wondered why so many potters have such a fear of plaster in
| the studio. I know it stems from a lack of education. Or from being
| mis-informed or poorly educated.
|
| There is a wonderful relationship between plaster and clay, and clay and
| plaster. Having worked with this relationship for a long time I have come
| to have a respect for both materials and their unlimited potentials.
|
| Just as a side bar, the fear that many have of getting chunks of plaster
in
| their clay from a plaster wedging table surface surfaces many times on
this
| list and never ceases to amaze me. If the table is built correctrly and
the
| plaster mixed and poured correctly, there is really no problem. And yes, a
| chunk of plaster in your pot will cause the section of the pot to blow off
| due to the hydroscopic nature of plaster as well as to its expansion when
| the pot is fired. However, an old slip casting/mold making trick in
| adjusting for proper viscosity and specific gravity is too add a small
| amount of powdered plaster to the slip mix. The resulting adjusted mix
| never has been problematic in our shop on the times wse have needed to use
| this method.
|
| Plaster is one of those underused, underestimated and over feared
materials
| that is of such benefit to potters, often maligned because of
mis-education
| and mis-information.
|
| Jonathan
|
| Jonathan Kaplan, president
| Ceramic Design Group
| PO Box 775112
| Steamboat Springs CO 80477
| voice and fax 970 879-9139
| jonathan@csn,net
| http://www.sni.net/ceramicdesigin

mel jacobson on wed 26 jul 00

after 35 years of teaching clay in a high school, the mere
mention of plaster gave me shivers. if it is possible, a high school kid
will get plaster in clay.
it always shows up in the big fount i make for a church.
worth a great deal of money, and i did not make two. they need it for
easter and i fire on good friday.....huge plaster pop right in the middle.
(use a big black marker, grinder, more felt pen. re/do the commission.
if you work alone, know how to control plaster, it is a wonderful
tool for potters. as for me, never have a drop in my studio. it will find
me, no matter what i do.
mel

http://www.pclink.com/melpots
written from the farm in wisconsin

James Bledsoe on wed 26 jul 00

plaster is just calcium

when we wedge on plaster and it comes off in molecules it is a little flux
in the clay no problem

Tom Buck on thu 27 jul 00

James B:
My reading of your post, that plaster is calcium, makes me say "Ah
no"
----
Plaster (of Paris) starts off as a mineral, a natural deposit of
calcium sulfate anhydrous or duohydrate (2H2O, aka gypsum). As such
neither will react with water (set) to form familiar molds. For this to
happen the mineral is processed into calcium sulfate, hemi-hydrate
(0.5H2O), pulverized, etc. The bags of plaster that potters receive have a
shelf-life of approx. six months, or less, depending on storage conditions
(low moisture helps).
When a measured amount of PP is added to a known amount of water,
the PP becomes a form of gypsum, that is, it becomes an "ordered" solid
(crystalline) that is strong and durable. Like the mixing of concrete, the
ratio of water to plaster is critical to getting a durable solid.
For potters, I suggest that the best source of info on forming
plaster shapes, is the book by Donald Frith, namely "mold making for
ceramics".
peace. tom b.
Tom Buck ) tel: 905-389-2339
(westend Lake Ontario, province of Ontario, Canada).
mailing address: 373 East 43rd Street,
Hamilton ON L8T 3E1 Canada

Millie Carpenter on fri 28 jul 00

Tom

does plaster plaster come with sell by dates or experation dates? I don't remember
seeing a code on previous bags.

Millie in Md.


>> The bags of plaster that potters receive have ashelf-life of approx. six months, or
>> less, depending on storage conditions (low moisture helps).
>>
>>

Janet Kaiser on fri 28 jul 00

I was so cold by the time I got to bed last night, I
could not get to sleep and so lay there thinking
beautiful thoughts...

Suddenly "plaster" popped up. (Yes, I know "Get a
life"). Apart from mulling over someone thinking
plaster is calcium (isn't it calcinated or dehydrated
gypsum?)

Anyway, it took me back to a big mega buck bid I worked
on at a petro-chemical engineering company in Germany
back in the early 1980s. They were introducing new
technology which would reduce pollution at a refinery
in the Soviet Union.

The bi-product of the proposed
Rauchgasentschwefelungsanlage (yes, that is one word)
was high grade plaster.

So all you folk who presume plaster is only made from
squeaky clean and natural products like gypsum please
beware. As far as I remember, the only way this other
plaster (which presumably would contain heavy metals
and other nasties like dioxins) differed from high
quality Plaster of Paris, was a slight yellow tinge. It
was also a tad softer than P.o.P. but equally
durable.

This technology was licensed from a firm in the US. It
was 1982/3 and I left in 1984/5, so I do not know how
many of these Rauchgasentschwefelungsanlagen went into
production around the world. Again I can only presume
some did, because it was at a time when many
manufacturing companies were being forced by
legislation and the environmental lobby to clean up
their act.

Just thought it worth a mention... Please do not ask me
the finer technical points. It is so long ago and you
know how those little grey cells drop everything they
need not remember. I also have difficulty telling you
anything from that previous life in English... That
part of my brain only works in German! :-)

Janet Kaiser - Also thinking of Joyce and her owls.
Does she realise how many people collect ceramic owls?
Now the word is out, there will be owl fanciers
arriving in droves. Hope they do not trample the desert
flat...

The Chapel of Art . Capel Celfyddyd
HOME OF THE INTERNATIONAL POTTERS' PATH
Criccieth LL52 0EA, GB-Wales Tel: (01766) 523570
E-mail: postbox@the-coa.org.uk
WEBSITE: http://www.the-coa.org.uk

Ingeborg Foco on sun 24 feb 02

I'm having difficulty locating Pottery #1 plaster for my new =
wedging/recycling table. The only thing available locally seems to be =
Uni Kal Veneer Plaster.
The ingredients are Plaster of Paris, Calcium Hydroxide and quarts. Is =
there anyone who has experience in using veneer plaster for a wedging =
table and hump molds? =20

Thanks in advance for any information.

Sincerely,

Ingeborg

John Rodgers on wed 2 jan 08

Bill,

I love my plaster bats. I started using them not long after I started
throwing on the wheel. Up until then my use of plaster has been in the
real of molds and mold making.

My throwing bats are made up from the "pure and Simple" bat system,
which consists of refomed plastic molds for the bats, and two different
sized keyways that fasten to the wheel head. Though I have used a lot of
other kinds of bats, mostly when I'm elsew3here and throwing, when I'm
in my studio I much prefer the plaster bats. I hear a lot of talk about
how plaster will get in the clay, etc, but I have never had that problem
when throwing, nor having it get into the scrap from throwing. I'm still
throwing with plaster bats I made up over ten years ago.

Two features I especially like are the ability to do a bit of wedging on
the bat while at the wheel, to remove any excess water and dry the clay
a bit, and I especially like the self releasing feature when the clay
object is dried on the base just a bit by the plaster, to the point that
the clay loses it's grip on the bat.and pops loose. It makes for a very
nice, smooth bottom. If the vessel is thrown well, there is no need to
trim out the bottom. of vessel.

Regards,

John Rodgers
Chelsea, aL

Bill Merrill wrote:
> Steve,
>
>
>
> I have used plaster bats since 1966. I took plaster class at Alfred in
> '73 and it was an eye opener to really learn how to make and use
> plaster. Wally Higgins was a great teacher. I have used plaster bats
> that I cast and the molds were part of the system Ted Randall developed
> in '49. There is a removable wheel head and flat heads for the Randall
> wheel. The bucket head accepts bats made from aluminum bat molds. I
> use 8", 12" 16" and 20 inch plaster bats. It is very convenient to
> throw pitchers for example on a bat, lift off the bat , let it set and
> trim it while still attached to the mold and then put it back on the
> wheel and trim the base if necessary. To remove the pitcher from the
> wheel I merely slide a thin, sharpened spatula under the pot and turn
> the wheel which pops off the pitcher from the bat. Not many people know
> this system, because there aren't any New Randall wheels being made. I
> am going to get a Soldner wheel and have them put on a tapered shaft so
> I can use use the bucket heads I have. A nice thing about plaster is it
> draws moisture out of the bottom of the pot and is similar in hardness
> to the walls of the pot. It is also convenient for Casseroles so if you
> have to adjust the lip you can as the can be turned upside down to see
> if it fits before cutting it off the bat. I guess I am just someone
> from an old school of potters and will continue to use plaster in my
> ceramics. Dave Shaner, Bob Turner, Val Cushing, Victor Babu, Ken
> Ferguson were just a few well known potters that used plaster bats. I
> have found that the use of bats this way raised my production
> tremendously.
>
>
>
> Regards,
>
>
>
> Bill Merrill
>
>
>
> ______________________________________________________________________________
> Clayart members may send postings to: clayart@lsv.ceramics.org
>
> You may look at the archives for the list, post messages, or change your
> subscription settings here: http://www.acers.org/cic/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at melpots2@visi.com
>
>
>

Bill Merrill on wed 2 jan 08

Steve,

=20

I have used plaster bats since 1966. I took plaster class at Alfred in
'73 and it was an eye opener to really learn how to make and use
plaster. Wally Higgins was a great teacher. I have used plaster bats
that I cast and the molds were part of the system Ted Randall developed
in '49. There is a removable wheel head and flat heads for the Randall
wheel. The bucket head accepts bats made from aluminum bat molds. I
use 8", 12" 16" and 20 inch plaster bats. It is very convenient to
throw pitchers for example on a bat, lift off the bat , let it set and
trim it while still attached to the mold and then put it back on the
wheel and trim the base if necessary. To remove the pitcher from the
wheel I merely slide a thin, sharpened spatula under the pot and turn
the wheel which pops off the pitcher from the bat. Not many people know
this system, because there aren't any New Randall wheels being made. I
am going to get a Soldner wheel and have them put on a tapered shaft so
I can use use the bucket heads I have. A nice thing about plaster is it
draws moisture out of the bottom of the pot and is similar in hardness
to the walls of the pot. It is also convenient for Casseroles so if you
have to adjust the lip you can as the can be turned upside down to see
if it fits before cutting it off the bat. I guess I am just someone
from an old school of potters and will continue to use plaster in my
ceramics. Dave Shaner, Bob Turner, Val Cushing, Victor Babu, Ken
Ferguson were just a few well known potters that used plaster bats. I
have found that the use of bats this way raised my production
tremendously.

=20

Regards,

=20

Bill Merrill

=20

Rogier Donker on thu 3 jan 08

Hey Bill :-)

All this talk about bats.... I was beginning to think
I was in the minority when it came to throwing on plaster bats. Like
you I "grew up " with plaster bats. The Amaco wheels all used to
come with the Ted Randall system. "Special head and bat casting ring"
One made their own bats as part of the ceramic process. Back then
(the sixties) everybody who was anybody on the ceramic scene threw on
plaster bats. Some of the bats in my studio are over thirty years
old... still going strong, thank you. Sometimes I think the old ways
are a lot better than the modern newfangled ways. Then again that is
probably an argument that the generation before us had too...;-) Time
marches on. My kiln, "Mama Martha." is up for sale... (located in
Southwest Indiana)

Rogier

P.S. See us on the web at http://www.donkerstudio.org

James and Sherron Bowen on thu 3 jan 08

How does one make a casting ring for these types of wheel heads? I have an
Amaco and a Randall. I don't have the "bucket" head for the Randall but
would love to find one.
JB
----- Original Message -----
From: "Rogier Donker"
To:
Sent: Thursday, January 03, 2008 7:37 AM
Subject: plaster

C.T. Wagoner on thu 3 jan 08

Hi JB,

Amaco sells the ring for their wheel head. I have four if you would like to
borrow them. It is handy to make them three of four at a time. Make them
upside down on a pane of glass. Use Hydro-cal or Ultra-cal for long lasting
hard bats.

Chuck the Billie Creek Potter

-------------------------------------------------------------------

How does one make a casting ring for these types of wheel heads? I have an
Amaco and a Randall. I don't have the "bucket" head for the Randall but
would love to find one.
JB
-

Rogier Donker on sat 5 jan 08

Yo! JB!

Amaco sells the casting rings for the special heads... 1 800 925
5195 "Tammy" at extension 322

Rogier

P.S. See us on the web at http://www.donkerstudio.org

Bill Merrill on fri 29 aug 08

There continues to be questions about plaster and how bad it is in the =
studio. Good potters for as long as I have been working in clay (48 =
years) use plaster wedging tables, plaster bats and plaster molds. I =
think that in most cases, the person mixing plaster doesn't have the =
experience of using plaster with the correct plaster to water ratio. =20

=20

If you use the following formula to mix your plaster (# 1 potters =
plaster) you won't have a problem.

=20

For every 80 cubic inches of plaster you need one quart of water and 2 =
=BE pounds of plaster.

=20

8" x 10" x 1" =3D 80 cubic inches. For every 80 cubic inches you need, =
use 2 =BE ( to 3) pounds of plaster. This will give=20

a good mix for plaster bats, molds etc. =20

=20

Hand sift the plaster into the water. Let it sit several minutes so the =
plaster is absorbed into the water. =20

Put your hand under the surface of the mix and agitate the mixture. Let =
it sit several minutes and mix again.=20

A good time to pour the plaster is when you get a small peak when you =
drag your finger across the mix.=20

Just don't pour when the mix is a watery slurry. Tap the bucket to the =
floor do get rid of air bubbles. =20

Tap the mold also to get any air bubbles of the surface of your mold =
form after you pour the plaster.

=20

Plaster sets up under water. Don't let it sit or pour it somewhere that =
you don't want it to set up.

Don't use old plaster. Sifting the lumps out doesn't work. Use fresh =
plaster. =20

Don't try and release the plaster from the mold until it has passed the =
heating stage. Plaster is weak then.

=20

=20

=20

=20

=20

Randall Moody on thu 25 sep 08

I have poured my plaster for my wedging area on my work bench last week and
was wondering if anyone had a rule of thumb on how long it takes for
something that is about 18 x 24 x 1.5 inches large to dry to a point where
it can be used. It has bee pretty dry here in Atlanta (no rain) since then
but I don't want to rush it.

--
Randall in Atlanta

Dawn Kleinman on thu 25 sep 08

I just did mine too. About the same size. Probably supposed to wait a week
or so. Nope, not me. No patience. I waited 3 days. It works great. And I
have the number for the gypsum guy. Doug 484-431-2201. He is very
knowledgable and was very helpful

You can see a pic of my table at work if I attached it correctly.

Good Luck
Dawn

On Thu, Sep 25, 2008 at 1:20 PM, Randall Moody wrote:

> I have poured my plaster for my wedging area on my work bench last week and
> was wondering if anyone had a rule of thumb on how long it takes for
> something that is about 18 x 24 x 1.5 inches large to dry to a point where
> it can be used. It has bee pretty dry here in Atlanta (no rain) since then
> but I don't want to rush it.
>
> --
> Randall in Atlanta
>

James F on thu 25 sep 08

Randall...

I've spent the last few of weeks pouring moulds and various textured slabs.=
My 16" x 16" x 1.5" slabs have been taking about a week outside in the su=
n and wind to dry (Michigan=2C relatively humid). Drying time seems to go =
up exponentially with thickness. A 2.25" thick slab is finally almost dry =
after almost 2 weeks. Some 8 x 8 x 15" moulds took over 3 weeks of alterna=
ting indoors and outdoors drying. My 24" x 24" x 4" wedging table slab too=
k almost 6 months to dry in my semi-heated studio (70 degrees day=2C 55 deg=
rees night).

You will know when they are ready. They seem to stay wet forever=2C then v=
ery quickly go from wet to dry. They stay cool and clammy for quite some t=
ime. One day they will feel noticably less clammy=2C and typically the nex=
t day they are dry. The sound when you tap them changes also=2C from a dul=
l "thunk" when wet to a higher pitched "think" sound (sorry=2C onomatopoeia=
is not my area of expertise!) when dry.

Also=2C it isn't rocket science. If the clay sticks=2C the plaster was too=
wet. Scrape it and wait a bit longer.

Hope it helps.

Be well.

...James

> Date: Thu=2C 25 Sep 2008 13:20:41 -0400
> From: randall.moody@GMAIL.COM
> Subject: Plaster
> To: CLAYART@LSV.CERAMICS.ORG
>=20
> I have poured my plaster for my wedging area on my work bench last week a=
nd
> was wondering if anyone had a rule of thumb on how long it takes for
> something that is about 18 x 24 x 1.5 inches large to dry to a point wher=
e
> it can be used. It has bee pretty dry here in Atlanta (no rain) since the=
n
> but I don't want to rush it.
>=20
> --
> Randall in Atlanta

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John Rodgers on thu 25 sep 08

Randall Moody wrote:
> I have poured my plaster for my wedging area on my work bench last week and
> was wondering if anyone had a rule of thumb on how long it takes for
> something that is about 18 x 24 x 1.5 inches large to dry to a point where
> it can be used. It has bee pretty dry here in Atlanta (no rain) since then
> but I don't want to rush it.
>
> --
> Randall in Atlanta
>
>
>
It's a lot like drying clay. If it still feels cool to touch , it's not
dry enough yet!

John Rodgers
Chelsea, AL

Fredrick Paget on thu 25 sep 08

If you can put it out in the sun it will dry in a few days and that
won't hurt it unless it gets over 120 degrees F .
If you can't move it probably dry enough to use in a couple of weeks
. Can be dried in moving air at not over 120 per US Gypsum
instructions.

Fred Paget

Twin Dragon Studio
Mill Valley, CA, USA
fredrick@well.com

Charter Member Potters Council

>I have poured my plaster for my wedging area on my work bench last week and
>was wondering if anyone had a rule of thumb on how long it takes for
>something that is about 18 x 24 x 1.5 inches large to dry to a point where
>it can be used. It has bee pretty dry here in Atlanta (no rain) since then
>but I don't want to rush it.
>
>--
>Randall in Atlanta

--

Jeff Longtin on thu 25 sep 08

Hey Randall,
There's no real science as to how long it should take to dry your slabs. (
though the "not cold to the touch" method is as good as any.)

The key to drying plaster fast is heat and air movement. I use a little room
heater in a metal shelving unit as my drying box. Too much heat, say above
100 degrees, and you can affect durability, but the biggie is moving the air. A
fan, if nothing else, will speed up the process.

take care

Jeff


In a message dated 9/25/2008 1:18:48 P.M. Central Daylight Time,
randall.moody@GMAIL.COM writes:

I have poured my plaster for my wedging area on my work bench last week and
was wondering if anyone had a rule of thumb on how long it takes for
something that is about 18 x 24 x 1.5 inches large to dry to a point where
it can be used. It has bee pretty dry here in Atlanta (no rain) since then
but I don't want to rush it.

--
Randall in Atlanta





**************Looking for simple solutions to your real-life financial
challenges? Check out WalletPop for the latest news and information, tips and
calculators. (http://www.walletpop.com/?NCID=emlcntuswall00000001)

Ric Swenson on fri 26 sep 08

When I made my plaster clay drying box, I made a plywood box about 10 inches deep and 18 X 24 inches -length/width. I used 3/4 inch marine plywood. I sealed the edges with moist clay.. then I drove some wall board screws into the bottom...inside the box. about 20 screws. Drove them about 1/2 inch into the plywood. Then took an electric pipe thawing tape and laced it around the screws so that the heat tape was spaced out across the bottom in a series of "S" shapes. I ran the plug to the outside of the box through a drilled hole.....and sealed the space around the electric cord with moist clay.






Then I mixed up pottery Plaster # 1 in a large plastic bin and poured the plaster into the box to a depth of about 6 inches. I let it set up for a few days and then plugged in the heat tape. When I re-cycled trimming and scraps from the slop bucket I used a jiffy mixer to get rid of any lumps and then poured the slip into the box. Then just plug in the tape.






This method has worked well for many years. The use of the heat tape doesn't seem to have damaged the plaster that I can tell. I only have to re-cycle about once a month....but the plaster dries the clay to a wedge-able condition in just a short time.






My kneading/wedging table was made in a similar way but the box was filled to the top and screeded level. I screwed a 2 X 2 to the side of the box and used eye screws to stretch a wedging wire tight from the top of the 18 inch post down to the side of the box. I used a small cable tightener to keep the stainless steel downrigger wire tight.





Ric


> > I have poured my plaster for my wedging area on my work bench last week and> > was wondering if anyone had a rule of thumb on how long it takes for> > something that is about 18 x 24 x 1.5 inches large to dry to a point where> > it can be used. It has bee pretty dry here in Atlanta (no rain) since then> > but I don't want to rush it.> >> > --> > Randall in Atlanta> >
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Frank Colson on fri 26 sep 08

Come-on! What's with this drying plaster for days and weeks gig? A soft
warm blowing air (heater fan, etc.) will dry plaster in a few hours.
The ultimate test: place your tongue on it (after assumed dried). If it
"sticks" to the surfarce, it is ready for use!

I have made more than 1000 plaster molds of every description and thickness
in my profession - as the saying goes: "practice makes perfect"

Frank Colson

----- Original Message -----
From: "James F"
To:
Sent: Thursday, September 25, 2008 12:57 PM
Subject: Re: Plaster


Randall...

I've spent the last few of weeks pouring moulds and various textured slabs.
My 16" x 16" x 1.5" slabs have been taking about a week outside in the sun
and wind to dry (Michigan, relatively humid). Drying time seems to go up
exponentially with thickness. A 2.25" thick slab is finally almost dry
after almost 2 weeks. Some 8 x 8 x 15" moulds took over 3 weeks of
alternating indoors and outdoors drying. My 24" x 24" x 4" wedging table
slab took almost 6 months to dry in my semi-heated studio (70 degrees day,
55 degrees night).

You will know when they are ready. They seem to stay wet forever, then very
quickly go from wet to dry. They stay cool and clammy for quite some time.
One day they will feel noticably less clammy, and typically the next day
they are dry. The sound when you tap them changes also, from a dull "thunk"
when wet to a higher pitched "think" sound (sorry, onomatopoeia is not my
area of expertise!) when dry.

Also, it isn't rocket science. If the clay sticks, the plaster was too wet.
Scrape it and wait a bit longer.

Hope it helps.

Be well.

...James

> Date: Thu, 25 Sep 2008 13:20:41 -0400
> From: randall.moody@GMAIL.COM
> Subject: Plaster
> To: CLAYART@LSV.CERAMICS.ORG
>
> I have poured my plaster for my wedging area on my work bench last week
> and
> was wondering if anyone had a rule of thumb on how long it takes for
> something that is about 18 x 24 x 1.5 inches large to dry to a point where
> it can be used. It has bee pretty dry here in Atlanta (no rain) since then
> but I don't want to rush it.
>
> --
> Randall in Atlanta

_________________________________________________________________
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John Rodgers on fri 26 sep 08

Frank is right.

I bought a 6 foot long chromed bakers rack on wheels from Sams for $72.
It came with 6 wired shelves that can hold 300 lbs each. I got the
special dust cover that goes with it - an additional $20-$25. . Slips
over it like a coat and and zips up tight - a form fit. I cut an
opening in the top to serve as a vent, and I dry my molds on the rack. I
speed the process by placing a small heater with a fan on the floor
underneath or on the bottom rack, depending, and let the heated air rise
up through the rack, venting out through the top. I also vent the output
side of my de-humidifier through the bakers rack. The air is dry and
warm and moving. Speeds drying tremendously. They will be done and ready
to use in just a few hours.

Big manufacturers of molds for production use these principals. They
will have drying room, with de-humidified, warm, circulating air coming
in at one end, passing over the molds, and venting out at the other
to carry off the moisture picked up from the molds. Anyone making molds
can do the same thing on a smaller scale, as I have.

Regards,

John Rodgers
Chelsea, AL

Frank Colson wrote:
> Come-on! What's with this drying plaster for days and weeks gig? A
> soft
> warm blowing air (heater fan, etc.) will dry plaster in a few hours.
> The ultimate test: place your tongue on it (after assumed dried).
> If it
> "sticks" to the surfarce, it is ready for use!
>
> I have made more than 1000 plaster molds of every description and
> thickness
> in my profession - as the saying goes: "practice makes perfect"
>
> Frank Colson
>
> ----- Original Message -----
> From: "James F"
> To:
> Sent: Thursday, September 25, 2008 12:57 PM
> Subject: Re: Plaster
>
>
> Randall...
>
> I've spent the last few of weeks pouring moulds and various textured
> slabs.
> My 16" x 16" x 1.5" slabs have been taking about a week outside in the
> sun
> and wind to dry (Michigan, relatively humid). Drying time seems to go up
> exponentially with thickness. A 2.25" thick slab is finally almost dry
> after almost 2 weeks. Some 8 x 8 x 15" moulds took over 3 weeks of
> alternating indoors and outdoors drying. My 24" x 24" x 4" wedging table
> slab took almost 6 months to dry in my semi-heated studio (70 degrees
> day,
> 55 degrees night).
>
> You will know when they are ready. They seem to stay wet forever,
> then very
> quickly go from wet to dry. They stay cool and clammy for quite some
> time.
> One day they will feel noticably less clammy, and typically the next day
> they are dry. The sound when you tap them changes also, from a dull
> "thunk"
> when wet to a higher pitched "think" sound (sorry, onomatopoeia is not my
> area of expertise!) when dry.
>
> Also, it isn't rocket science. If the clay sticks, the plaster was
> too wet.
> Scrape it and wait a bit longer.
>
> Hope it helps.
>
> Be well.
>
> ...James
>
>> Date: Thu, 25 Sep 2008 13:20:41 -0400
>> From: randall.moody@GMAIL.COM
>> Subject: Plaster
>> To: CLAYART@LSV.CERAMICS.ORG
>>
>> I have poured my plaster for my wedging area on my work bench last week
>> and
>> was wondering if anyone had a rule of thumb on how long it takes for
>> something that is about 18 x 24 x 1.5 inches large to dry to a point
>> where
>> it can be used. It has bee pretty dry here in Atlanta (no rain) since
>> then
>> but I don't want to rush it.
>>
>> --
>> Randall in Atlanta
>
> _________________________________________________________________
> Want to do more with Windows Live? Learn "10 hidden secrets" from Jamie.
> http://windowslive.com/connect/post/jamiethomson.spaces.live.com-Blog-cns!550F681DAD532637!5295.entry?ocid=TXT_TAGLM_WL_domore_092008=
>
>
>

Shula on fri 26 sep 08

Several people have mentioned that the temperature shouldn't go above 120. Is that only when the plaster is curing? May I assume that it won't harm the plaster if the temp goes over 120 once it is cured? Why do I ask? I live in the desert where the temp in my garagio has been known to get over 120!

Thanks

Shula
Desert Hot Springs, California USA

-----Original Message-----
>From: Fredrick Paget

>
>If you can put it out in the sun it will dry in a few days and that
>won't hurt it unless it gets over 120 degrees F .

Ivor and Olive Lewis on sat 27 sep 08

Dear Shula,
Cured plaster should not be heated or it will decompose.
Various grades of Plaster are made by heating a mineral containing
Calcium Sulphate, usually Gypsum, which has a molecular formula of
CaSO4.2H2O. This removes Water of Crystallisation.
The powder we buy is dehydrated Calcium Sulphate. This powder
rehydrates when mixed with water and new crystals grow. This is what
happens as the plaster sets. If heated beyond 120 deg C . Water is
driven from the solid and it becomes fragile and will disintegrate. at
about 120 C three quarters of the water is driven from the solid mass.
Best regards,
Ivor Lewis.
Redhill,
South Australia.

Ric Swenson on sat 27 sep 08

Ivor,


Tto decompose plaster in the bronze casting process it takes a LOT more than 120 degrees to decompose the plaster. at least in a real world situation. Science says one thing and reality is sometimes quite different....at least to us simple potters. To melt out the wax forms we fired them for overnight at above 600 degrees to end up with decomposed plaster.....that we then poured hot bronze into to make our sculptural works.


So...what works is good. I found that it takes quite a high temperature to make ludo (sp?) from plaster. At bennington Potters, we cooked our old ceramical ram press molds under direct gas flames for 'days' to make them breakable from the then later salvaged steel reinforcing frames.

Drying a plaster batt can be done safely using an anti freezing heat tape....with little effect ...at least on the surface of the plaster.....which is the only place it counts for me. Maybe some other reaction is happening further down in the plaster? Who cares? Thirty years later I can afford to cast another if I need it.


My 2 yuan,


Ric



Richard H. ("Ric") Swenson, Teacher, Office of International Cooperation and Exchange of Jingdezhen Ceramic Institute, TaoYang Road, Eastern Suburb, Jingdezhen City.JiangXi Province, P.R. of China. Postal code 333001. Mobile/cellular phone : 86 13767818872 < RicSwenson0823@hotmail.com> http://www.jci.jx.cn/http://www.ricswenson.com



> Date: Sat, 27 Sep 2008 15:58:41 +0930> From: iandol@WESTNET.COM.AU> Subject: Plaster> To: CLAYART@LSV.CERAMICS.ORG> > Dear Shula,> Cured plaster should not be heated or it will decompose.> Various grades of Plaster are made by heating a mineral containing> Calcium Sulphate, usually Gypsum, which has a molecular formula of> CaSO4.2H2O. This removes Water of Crystallisation.> The powder we buy is dehydrated Calcium Sulphate. This powder> rehydrates when mixed with water and new crystals grow. This is what> happens as the plaster sets. If heated beyond 120 deg C . Water is> driven from the solid and it becomes fragile and will disintegrate. at> about 120 C three quarters of the water is driven from the solid mass.> Best regards,> Ivor Lewis.> Redhill,> South Australia.
_________________________________________________________________
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James F on sat 27 sep 08

Ric...

I think folks are beginning to talk apples and oranges here. While the pla=
ster will retain it's structural integrity after moderate heating=2C meanin=
g it will still function as=2C say=2C a hump mold=2C beyond 125 degrees F i=
t=2C according to the tech folks at USG=2C loses much of it's absorbent cha=
racteristics which renders it unsuitable for slip casting. In hump mouldin=
g and investment casting=2C this absorbency is less important or even unimp=
ortant. Also=2C I think Ivor was talking Celsius rather than Fahrenheit. =
=20

Also=2C though a bit off topic=2C there is a trick my dad used when lost wa=
x casting to easily remove the plaster shell: After casting=2C and while t=
he retaining ring/investment plaster form/casting was still fairly hot=2C h=
e would plunge the entire thing into water. The plaster disintegrated inst=
antly and flowed out of the retaining ring like lava=2C leaving him with a =
clean ring and casting. I'm sure a variation of this procedure would work =
for your ram press moulds.

Be well.

...James

> Date: Sat=2C 27 Sep 2008 20:59:49 +0800
> From: ricswenson0823@HOTMAIL.COM
> Subject: Re: Plaster
> To: CLAYART@LSV.CERAMICS.ORG
>=20
> Ivor=2C
>=20
>=20
> Tto decompose plaster in the bronze casting process it takes a LOT more t=
han 120 degrees to decompose the plaster. at least in a real world situati=
on. Science says one thing and reality is sometimes quite different....at =
least to us simple potters. To melt out the wax forms we fired them for ove=
rnight at above 600 degrees to end up with decomposed plaster.....that we t=
hen poured hot bronze into to make our sculptural works.
>=20
>=20
> So...what works is good. I found that it takes quite a high temperature =
to make ludo (sp?) from plaster. At bennington Potters=2C we cooked our ol=
d ceramical ram press molds under direct gas flames for 'days' to make them=
breakable from the then later salvaged steel reinforcing frames.
>=20
> Drying a plaster batt can be done safely using an anti freezing heat tape=
....with little effect ...at least on the surface of the plaster.....which =
is the only place it counts for me. Maybe some other reaction is happening=
further down in the plaster? Who cares? Thirty years later I can afford =
to cast another if I need it.
>=20
>=20
> My 2 yuan=2C
>=20
>=20
> Ric
>=20
>=20
>=20
> Richard H. ("Ric") Swenson=2C Teacher=2C Office of International Cooperat=
ion and Exchange of Jingdezhen Ceramic Institute=2C TaoYang Road=2C Eastern=
Suburb=2C Jingdezhen City.JiangXi Province=2C P.R. of China. Postal code 3=
33001. Mobile/cellular phone : 86 13767818872 < RicSwenson0823@hotmail.com>=
http://www.jci.jx.cn/http://www.ricswenson.com
>=20
>=20
>=20
> > Date: Sat=2C 27 Sep 2008 15:58:41 +0930> From: iandol@WESTNET.COM.AU> S=
ubject: Plaster> To: CLAYART@LSV.CERAMICS.ORG> > Dear Shula=2C> Cured plast=
er should not be heated or it will decompose.> Various grades of Plaster ar=
e made by heating a mineral containing> Calcium Sulphate=2C usually Gypsum=
=2C which has a molecular formula of> CaSO4.2H2O. This removes Water of Cry=
stallisation.> The powder we buy is dehydrated Calcium Sulphate. This powde=
r> rehydrates when mixed with water and new crystals grow. This is what> ha=
ppens as the plaster sets. If heated beyond 120 deg C . Water is> driven fr=
om the solid and it becomes fragile and will disintegrate. at> about 120 C =
three quarters of the water is driven from the solid mass.> Best regards=2C=
> Ivor Lewis.> Redhill=2C> South Australia.
> _________________________________________________________________
> Explore the seven wonders of the world
> http://search.msn.com/results.aspx?q=3D7+wonders+world&mkt=3Den-US&form=
=3DQBRE

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Shula on sat 27 sep 08

Dear Ivor,

Thanks for the information. I am now considering bringing in my molds from the garage.

Shula

-----Original Message-----
>From: Ivor and Olive Lewis
>Sent: Sep 26, 2008 11:28 PM
>To: CLAYART@LSV.CERAMICS.ORG
>Subject: Plaster
>
>Dear Shula,
>Cured plaster should not be heated or it will decompose.
>Various grades of Plaster are made by heating a mineral containing
>Calcium Sulphate, usually Gypsum, which has a molecular formula of
>CaSO4.2H2O. This removes Water of Crystallisation.
>The powder we buy is dehydrated Calcium Sulphate. This powder
>rehydrates when mixed with water and new crystals grow. This is what
>happens as the plaster sets. If heated beyond 120 deg C . Water is
>driven from the solid and it becomes fragile and will disintegrate. at
>about 120 C three quarters of the water is driven from the solid mass.
>Best regards,
>Ivor Lewis.
>Redhill,
>South Australia.

Mike Gordon on sat 27 sep 08

Off the topic of clay use of plaster........ We also added sand and
fiberglass fiber to the investment for bronze casting and used the same
process of using water to break up the mold. Mike Gordon

James F on sat 27 sep 08

Sir...

Can you please expand upon your methods and equipage for our elucidation? =
I would love to be able to speed up the drying of large slabs and moulds to=
a couple of hours.

I placed three small solid plaster models=2C 4.5" diameter by 5.5 inch heig=
ht=2C in my commercial dehydrator set to 120 degrees. Even in this environ=
ment these small objects took in excess of 24 hours to dry. My larger slab=
s and moulds will not even fit in the dehydrator. These large pieces are e=
xposed to a constant soft warm breeze along with sunshine=2C and still they=
remain wet for the time spans mentioned. If a heater fan (?) will dry lar=
ge moulds faster than a dehydrator can dry my small ones=2C your methods wo=
uld provide a major step forward in both time and energy savings.

Also=2C how do you ensure that your heater fan does not exceed 125 degrees =
F=2C as I am told by the folks at US Gypsum that this temperature and beyon=
d will "kill" the plaster and render it unfit for slip casting.

Thank you in advance for your assistance.

All the best.

...James

> Date: Fri=2C 26 Sep 2008 09:42:03 -0700
> From: artact@COMCAST.NET
> Subject: Re: Plaster
> To: CLAYART@LSV.CERAMICS.ORG
>=20
> Come-on! What's with this drying plaster for days and weeks gig? A so=
ft
> warm blowing air (heater fan=2C etc.) will dry plaster in a few hours.
> The ultimate test: place your tongue on it (after assumed dried). If i=
t
> "sticks" to the surfarce=2C it is ready for use!
>=20
> I have made more than 1000 plaster molds of every description and thickne=
ss
> in my profession - as the saying goes: "practice makes perfect"
>=20
> Frank Colson
>=20
> ----- Original Message -----
> From: "James F"
> To:
> Sent: Thursday=2C September 25=2C 2008 12:57 PM
> Subject: Re: Plaster
>=20
>=20
> Randall...
>=20
> I've spent the last few of weeks pouring moulds and various textured slab=
s.
> My 16" x 16" x 1.5" slabs have been taking about a week outside in the su=
n
> and wind to dry (Michigan=2C relatively humid). Drying time seems to go =
up
> exponentially with thickness. A 2.25" thick slab is finally almost dry
> after almost 2 weeks. Some 8 x 8 x 15" moulds took over 3 weeks of
> alternating indoors and outdoors drying. My 24" x 24" x 4" wedging table
> slab took almost 6 months to dry in my semi-heated studio (70 degrees day=
=2C
> 55 degrees night).
>=20
> You will know when they are ready. They seem to stay wet forever=2C then=
very
> quickly go from wet to dry. They stay cool and clammy for quite some tim=
e.
> One day they will feel noticably less clammy=2C and typically the next da=
y
> they are dry. The sound when you tap them changes also=2C from a dull "t=
hunk"
> when wet to a higher pitched "think" sound (sorry=2C onomatopoeia is not =
my
> area of expertise!) when dry.
>=20
> Also=2C it isn't rocket science. If the clay sticks=2C the plaster was t=
oo wet.
> Scrape it and wait a bit longer.
>=20
> Hope it helps.
>=20
> Be well.
>=20
> ...James
>=20
> > Date: Thu=2C 25 Sep 2008 13:20:41 -0400
> > From: randall.moody@GMAIL.COM
> > Subject: Plaster
> > To: CLAYART@LSV.CERAMICS.ORG
> >
> > I have poured my plaster for my wedging area on my work bench last week
> > and
> > was wondering if anyone had a rule of thumb on how long it takes for
> > something that is about 18 x 24 x 1.5 inches large to dry to a point wh=
ere
> > it can be used. It has bee pretty dry here in Atlanta (no rain) since t=
hen
> > but I don't want to rush it.
> >
> > --
> > Randall in Atlanta
>=20
> _________________________________________________________________
> Want to do more with Windows Live? Learn =9310 hidden secrets=94 from Jam=
ie.
> http://windowslive.com/connect/post/jamiethomson.spaces.live.com-Blog-cns=
!550F681DAD532637!5295.entry?ocid=3DTXT_TAGLM_WL_domore_092008=3D

_________________________________________________________________
See how Windows connects the people=2C information=2C and fun that are part=
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Ivor and Olive Lewis on sun 28 sep 08

Dear Ric Swenson,
Who is using Gypsum Plaster as a mould material for the Lost Wax
Casting process ?
My metallurgical training and industrial experience with Robert
Hadfield and Sons, Deloro Stellite and the Wall Colmonoy Corporation
leads me to believe that you are not telling me the whole story about
the use of plaster as an investment compound for bronze casting.
Best regards,
Ivor Lewis.
Redhill,
South Australia.

Ric Swenson on sun 28 sep 08

Ludo...previously fired plaster is used to encapilsate the new plaster mold which is used to do the casting.....it saves material.....it is just old plaster....heated and then re-used to do the lost wax process.....a filler.



Hope we have not gone outside the bounds of how to make a plaster wedging table.....we are far afield from ceramics now....still with plaster...but plaster has so many uses.....pottery...ram pressing....casting....molds......bronze casting....and of course wedging tables...which was the original question....how to speed the time for making plaster cure.



Ric



"...then fiery expedition be my wing, ..." -Wm. Shakespeare, RICHARD III, Act IV Scene III Richard H. ("Ric") Swenson, Teacher, Office of International Cooperation and Exchange of Jingdezhen Ceramic Institute, TaoYang Road, Eastern Suburb, Jingdezhen City.JiangXi Province, P.R. of China. Postal code 333001. Mobile/cellular phone : 86 13767818872 < RicSwenson0823@hotmail.com> http://www.jci.jx.cn/http://www.ricswenson.com



> Date: Sat, 27 Sep 2008 15:33:29 -0700> From: clayart@EARTHLINK.NET> Subject: plaster> To: CLAYART@LSV.CERAMICS.ORG> > Off the topic of clay use of plaster........ We also added sand and> fiberglass fiber to the investment for bronze casting and used the same> process of using water to break up the mold. Mike Gordon
_________________________________________________________________
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Frank Colson on sun 28 sep 08

Just for the record! Plaster has been used as part of a composition
compound for bronze casting for eons! It is referred to as "lutto" which
is a 50/50 mixture of plaster and previously fired plaster. That is,
plaster which was exposed to molten metal once. The Greeks, the Romans, and
even contemporary art foundries have used it up into the early 50's when
"ceramic shell" became the truely definitive material to make investments
molds for casting bronze and other alloys. I researched ceramic shell for
10 years before it became available to the commercial
and studio community. Because of ceramic shell, today, a wax original can
be cast in bronze in 1 hour from scratch!

Today, I offer the entire process in "eBook" form available on www.R2D2u.com

Frank Colsn


----- Original Message -----
From: "Ivor and Olive Lewis"
To:
Sent: Saturday, September 27, 2008 11:27 PM
Subject: Re: Plaster


> Dear Ric Swenson,
> Who is using Gypsum Plaster as a mould material for the Lost Wax
> Casting process ?
> My metallurgical training and industrial experience with Robert
> Hadfield and Sons, Deloro Stellite and the Wall Colmonoy Corporation
> leads me to believe that you are not telling me the whole story about
> the use of plaster as an investment compound for bronze casting.
> Best regards,
> Ivor Lewis.
> Redhill,
> South Australia.

Randall Moody on sun 28 sep 08

Thanks to you all. You people are great! I waited a week and used the table
today with no problems at all. When I poured the plaster I put a square of
burlap in the middle to add a little strength since I wasn't sure how much
movement was in my table. Luckily I have a tendency to overbuild things so
the table is rock solid. The only issue that I have found is that I didn't
leave enough room at the area that would be the toe-kick so it will take
some getting used to. I may have to get out the jigsaw if it bugs me too
much.

The next issue that I had to deal with was an un-level wheel. I didn't
notice it when I was doing small bowls but I was making a couple of large
(20" or so) vases and they were getting out of hand. I thought it was just
me since I always think I am the weak link in the chain first. I recommend
that everyone get a small round "bullseye" spirit level even if you are
moving your wheel a foot or so.


--
Randall in Atlanta

John Rodgers on sun 28 sep 08

Please note that Ivor said 120C.....not 120F.

120C is equal to 248F.

I have been in the Desert Southwest. Never did I see it get even close
to that. Every scorpion, lizard and rattlesnake would be well done at
that temperature. And you and me both. You can cook fish at 150F

If your molds get to 120F you won't have a problem. They will just dry
out quickly for reuse - a big advantage to living in the Southwest. -
but not so much when you are trying to slow dry green ware.

Regards,

Jhn Rodgers

Shula wrote:
> Dear Ivor,
>
> Thanks for the information. I am now considering bringing in my molds from the garage.
>
> Shula
>
> -----Original Message-----
>
>> From: Ivor and Olive Lewis
>> Sent: Sep 26, 2008 11:28 PM
>> To: CLAYART@LSV.CERAMICS.ORG
>> Subject: Plaster
>>
>> Dear Shula,
>> Cured plaster should not be heated or it will decompose.
>> Various grades of Plaster are made by heating a mineral containing
>> Calcium Sulphate, usually Gypsum, which has a molecular formula of
>> CaSO4.2H2O. This removes Water of Crystallisation.
>> The powder we buy is dehydrated Calcium Sulphate. This powder
>> rehydrates when mixed with water and new crystals grow. This is what
>> happens as the plaster sets. If heated beyond 120 deg C . Water is
>> driven from the solid and it becomes fragile and will disintegrate. at
>> about 120 C three quarters of the water is driven from the solid mass.
>> Best regards,
>> Ivor Lewis.
>> Redhill,
>> South Australia.
>>
>
>
>

Ivor and Olive Lewis on mon 29 sep 08

Dear John Rodgers ,
Thank you for that reminder that in Oz we are metric while in the USA
you still cling to Imperial ways. Must remember to go back to my
former practice of including both. Have a hand calculator that
incorporates conversion programs so it is no hardship.
Best regards,
Ivor Lewis.
Redhill,
South Australia.


<>

Des & Jan Howard on mon 29 sep 08

Ivor
Time passes, practices change.
Gypsum plaster plus powdered silica is a standard mould mix used in
studio & workshop glass casting. The temperatures used are comparable to
bronze casting, around 950-1000C.
Des

Ivor and Olive Lewis wrote:
> Who is using Gypsum Plaster as a mould material for the Lost Wax
> Casting process ?
> My metallurgical training and industrial experience with Robert
> Hadfield and Sons, Deloro Stellite and the Wall Colmonoy Corporation
> leads me to believe that you are not telling me the whole story about
> the use of plaster as an investment compound for bronze casting.

--
Des & Jan Howard
Lue Pottery
Lue NSW
Australia
2850

02 6373 6419
www.luepottery.hwy.com.au

Bill Merrill on wed 16 sep 09

John Rodgers has it right about plaster bats. If only there were =3D
Randall wheel heads made for other wheels. Production would be raised, =
=3D
Few cracks in the bottom of pots etc. I have 8", 12"'16" and 20" =3D
plaster bats and wouldn't use anything else. Plaster is a potters =3D
friend for mold making and plaster bats. F people would just learn how =3D
to use them. There are plaster bats on the wheels where I teach and I =3D
have used the same wheels for 39 years and they are like new. Everyone =3D
makes some plaster bats for themselves. We have more than one bat mold =3D
for each size so multiples can be poured at the same time. Yes, they =3D
take up some room, but losing a little space is nothing to what the =3D
advantages are with plaster bats.

=3D20

Blue bird may start making wheel heads and mold rings after I just had =3D
them make a Soldner P400 wheel for me that they made a shaft for their =3D
wheel and turned it to fit my Randall wheel heads. =3D20

=3D20

If more potters that are interested in raising their productivity would =3D
seriously give plaster bats a chance.

=3D20

On a wheel, I secured a piece of 3'4' plywood to the flat head. =3D
The plywood had an 1" diameter hole drilled out of the middle. A =3D
Randall bucket head was tapped on center and was secured to the plywood =3D
using screws. The hole in the center was so the wheel head shaft =3D
(short) would fit flush against the plywood. This worked like a charm.=3D2=
0

=3D20

There are so many advantages to using plaster bats ......I think a =3D
younger generation of potters don't know what they are missing.

=3D20

When mixing plaster for every quart of water use 2 =3DBE pounds of =3D
plaster. The plaster will be a good hardness. For every 80 cubic =3D
inches of plaster you need=3D3D 1 quart of water =3D3D 2 =3DBE pounds of =
=3D
plaster.

=3D20

This post is only for information and my opinion, not to start a =3D
negative dialog. =3D20

John Rodgers on fri 13 aug 10

Very likely.

John

John Rodgers
Clayartist and Moldmaker
88'GL VW Bus Driver
Chelsea, AL
Http://www.moldhaus.com


On 8/13/2010 9:17 PM, Tara Mooney wrote:
> Hi all,
>
> If I try to make a hump mold using a ceramic bowl as
> the form, will the expansion of the plaster cause the
> ceramic bowl to crack?
>
> Thanks,
> Tara
>
>

Tara Mooney on fri 13 aug 10

Uggh, I am looking to re-produce a part of a particular curve
of this bowl. Just the bottom.
How do I get around that.
I absolutely cannot loose the original.
Thanks.

On Aug 13, 2010, at 11:40 PM, John Rodgers wrote:

> Very likely.
>
> John
>
> John Rodgers
> Clayartist and Moldmaker
> 88'GL VW Bus Driver
> Chelsea, AL
> Http://www.moldhaus.com
>
>
> On 8/13/2010 9:17 PM, Tara Mooney wrote:
>> Hi all,
>>
>> If I try to make a hump mold using a ceramic bowl as
>> the form, will the expansion of the plaster cause the
>> ceramic bowl to crack?
>>
>> Thanks,
>> Tara
>>
>>
>

Tara Mooney on fri 13 aug 10

Hi all,

If I try to make a hump mold using a ceramic bowl as
the form, will the expansion of the plaster cause the
ceramic bowl to crack?

Thanks,
Tara

Fredrick Paget on sat 14 aug 10

Dont forget clay shrinkage in using a hump mold. You have to get it
off the hump before it drys enough to shrink or it will crack. And
even if you get one off intact it is going to shrink in firing so
the end result will me a shrunk down replica of the original bowl.
To get that curve you need to make a rib with the curve in it and
start 12 to 15 percent larger than the ceramic bowl you have. But
then you know this if you have worked with clay at all. I'm just
reminding you.

Fred
--
Twin Dragon Studio
Mill Valley, CA, USA

James Freeman on sat 14 aug 10

Tara...

I have cast plaster in a glass bowl without incident, but it was a
rather shallow bowl, and perhaps glass is more flexible than fired
clay. John R. is the mold making expert here, so if he says it will
break, you can probably take that to the bank.

As a possible solution to your problem, why not spray the inside of
your bowl with WD-40 (as a release agent), and pack the desired area
with fine-grained clay. Remove this clay, invert it onto a board
surrounded by cottles, and immediately (before any drying shrinkage
begins) pour a plaster negative mold over the wet clay form. When the
negative mold cures, you can cast your plaster positive inside the
plaster negative.

Just an idea.

...James

James Freeman

"All I say is by way of discourse, and nothing by way of advice.=3DA0 I
should not speak so boldly if it were my due to be believed."
-Michel de Montaigne

http://www.jamesfreemanstudio.com
http://www.flickr.com/photos/jamesfreemanstudio/
http://www.jamesfreemanstudio.com/resources




On Fri, Aug 13, 2010 at 11:46 PM, Tara Mooney wrote:
> Uggh, I am looking to re-produce a part of a particular curve
> of this bowl. Just the bottom.
> How do I get around that.
> I absolutely cannot loose the original.
> Thanks.
>

Jeff Jeff on sat 14 aug 10

Tara,

An alternative to filling the bowl with plaster, which will result in the
bowl cracking, is to COAT the inside of the bowl with plaster. (Such that
you can actually get a casting of the form.) A thin coating of plaster
expands but not nearly as much as a large block of plaster.

Once this first coating has hardened you can see about removing it from the
form. It will be fragile but it might allow you to get a casting without
damaging the piece.

Once you're able to remove the form you can then go back and add to its
thickness so that it's more durable.

Or you can then treat this plaster form as the original and begin the mold
making process anew.

take care

Jeff Longtin
Minneapolis



In a message dated 8/13/2010 10:32:41 P.M. Central Daylight Time,
taramooney@MAC.COM writes:

Hi all,

If I try to make a hump mold using a ceramic bowl as
the form, will the expansion of the plaster cause the
ceramic bowl to crack?

Thanks,
Tara

William & Susan Schran User on sat 14 aug 10

On 8/13/10 10:17 PM, "Tara Mooney" wrote:

> If I try to make a hump mold using a ceramic bowl as
> the form, will the expansion of the plaster cause the
> ceramic bowl to crack?

No problem with expansion of plaster cracking the bowl.
Must be certain to have adequate release agent covering surface that will b=
e
cast. Interior of bowl must be smooth and curve out all the way up the wall=
.
After plaster dries you may need to set bowl upside down on a towel or othe=
r
cushion and tap the rim of the bowl on a surface to release the plaster.

Bill

--
William "Bill" Schran
wschran@cox.net
wschran@nvcc.edu
http://www.creativecreekartisans.com

Snail Scott on sat 14 aug 10

On Aug 13, 2010, at 9:17 PM, Tara Mooney wrote:
> If I try to make a hump mold using a ceramic bowl as
> the form, will the expansion of the plaster cause the
> ceramic bowl to crack?


Not usually. It will help if you use
a mold release, and fill the bowl only
up to a 50% gradient slope or so. If
the slope of the bowl's side is low,
expansion will merely cause the plaster
to creep higher in the bowl. I use this
strategy when making outdoor bowls
for water. I never have a freeze crack,
and water expansion is way worse
than plaster. As long as there is a
wider area above the top of the plaster,
it will likely be OK, but the steeper the
slope, the more you need to let it be
slippery, i.e. good mold release.

-Snail

John Rodgers on tue 17 aug 10

James,

I have had a computer crash right in the middle of this.

It is a matter of how much risk one is willing to take with the original
bowl. If the bowl is something I would absolutely not want to lose -
your suggestion of using the clay is right on.

John


On 8/14/2010 6:46 AM, James Freeman wrote:
> Tara...
>
> I have cast plaster in a glass bowl without incident, but it was a
> rather shallow bowl, and perhaps glass is more flexible than fired
> clay. John R. is the mold making expert here, so if he says it will
> break, you can probably take that to the bank.
>
> As a possible solution to your problem, why not spray the inside of
> your bowl with WD-40 (as a release agent), and pack the desired area
> with fine-grained clay. Remove this clay, invert it onto a board
> surrounded by cottles, and immediately (before any drying shrinkage
> begins) pour a plaster negative mold over the wet clay form. When the
> negative mold cures, you can cast your plaster positive inside the
> plaster negative.
>
> Just an idea.
>
> ...James
>
> James Freeman
>
> "All I say is by way of discourse, and nothing by way of advice. I
> should not speak so boldly if it were my due to be believed."
> -Michel de Montaigne
>
> http://www.jamesfreemanstudio.com
> http://www.flickr.com/photos/jamesfreemanstudio/
> http://www.jamesfreemanstudio.com/resources
>
>
>
>
> On Fri, Aug 13, 2010 at 11:46 PM, Tara Mooney wrote:
>> Uggh, I am looking to re-produce a part of a particular curve
>> of this bowl. Just the bottom.
>> How do I get around that.
>> I absolutely cannot loose the original.
>> Thanks.
>>

Tara Mooney on wed 18 aug 10

Thank you so much to all that replied to my question!

I decided to go for it.
What I discovered in the unmolding process that my form
was not ceramic at all but glass.
Opaque colored glass made in Italy. I knew it was
glass, but I guess I had a very blonde moment the other day and
decided it was ceramic!
Well anyway, the plaster process discolored and disformed the bowl.
It turned a lighter shade where the plaster was but only on the outside.
I poured plaster in the inside.
Also this bowl has ridges on the outside and they flattened out a bit
up to the plaster line! The inside looks exactly the same.
Also there are some fine squiggly lines on the outside only.
They don't really look like cracks.

What happened? Was it the heat? Plaster heat can melt glass?
How is that possible?

Thanks again,
I would like multiple of this mold but I won't be trying that again.

Tara

Snail Scott on wed 18 aug 10

On Aug 18, 2010, at 2:41 PM, Tara Mooney wrote:
> ...the plaster process discolored and disformed the bowl.
> It turned a lighter shade where the plaster was but only on the
> outside.
> I poured plaster in the inside.
> Also this bowl has ridges on the outside and they flattened out a bit
> up to the plaster line! ... heat? Plaster heat can melt glass?



I seriously doubt that plaster could harm glass
in any way except breaking it entirely. The
temperatures are not nearly high enough!

I will suggest one possibility: in Italy, they make
a lot of pottery-shaped items which are not clay
or glass at all, but actually molded papier mache,
often brightly painted with traditional designs and
covered in a shiny coating. They really can look
like clay or carved wood or opaque glass or
almost anything. The sound is the main clue. Does
it sound a bit 'dull' like wood, and weigh relatively
little for its volume?

Unlike glass or clay, papier mache would be
affected by both the moisture and the pressure of
setting plaster. Just a wild guess; pretty sure
it isn't clay or glass, though, if plaster changed it
in any real way!

-Snail

Bill Merrill on mon 10 jan 11

For figuring out how much water and plaster ( number 1 potters plaster) =
=3D
are needed to fill a specific space use the following formula. The =3D
following formula can be reduced or increased using the basic formula.

=3D20

For every 80 cubic inches of space you will need 1 quart of cool water =3D
and 2 =3DBE pounds of plaster. You may get by with 2 3/8 pounds of =3D
plaster, but I find 2 =3DBE pounds of plaster make a good density.

=3D20

Example: 8" x 10" X 1" =3D3D 80 cubic inches

=3D20

For every 80 cubic inches use: 1 quart of water and 2 =3DBE pounds of =3D
plaster. =3D20

=3D20

Pour the plaster into the water by sifting . Let it set until the =3D
plaster is absorbed into the water. If you don't' stir it,

it will not start setting up right away. Agitate the plaster and water =
=3D
with your hand underneath the surface of the mix. The plaster will =3D
stand up like frosting when you drag you finger over it, that is a good =
=3D
time to pour. Depending on the mold you are pouring into. Tap the =3D
bucket before you pour and also tap the mold after pouring to get rid of =
=3D
air bubbles. =3D20

=3D20

Hot water will accelerate the hardening process. Cool water will harden =
=3D
more slowly. I use luke- warm water.

=3D20

=3D20

David Martin Hershey on tue 11 jan 11

Hi John,

Thanks for the alcohol in the plaster tip.
You mentioned this a few years back,
and I've used it ever since. Works great!

Re: spraying alcohol inside the mold,
does it re-wet the mold soap?
Or is the water in the alcohol not enough to do this.

Also, does it have any effect on a leather hard clay original?

Just had a D'oh! moment!

I have a glaze that foams in the ball mill.

I've tried anti foaming agent- didn't work.
But never thought to try alcohol afterwords...

Best, DMH

David Martin Hershey
DMH Studio + Design
2629 Manhattan Ave #137
Hermosa Beach CA USA
90254-2447 424.241.3809
http://www.dmhstudio.com/
http://www.obamacardgold.com
http://www.winetastingtrolley.com/

On 1/10/2011 10:16 PM, John Rodgers wrote:
> then just before pouring, spritz the surface
> of the mold lightly with the alcohol. This will break any remaining
> bubbles that may be trapped under the surface of the plaster that come
> forth when the plaster is poured.

John Rodgers on tue 11 jan 11

Bill,

I like to bump the bucket on the floor the same way one would bump a
cake mix to make the bubbles rise to the surface. The with the bubbles
on the surface, I like to spritz the bubbles with a light spray of
alcohol to break them up. then just before pouring, spritz the surface
of the mold lightly with the alcohol. This will break any remaining
bubbles that may be trapped under the surface of the plaster that come
forth when the plaster is poured. Once a good smooth bubble free contact
is made between the surface of the mold and the plaster, any remaining
small bubbles won't matter.

John

John Rodgers
Clayartist and Moldmaker
88'GL VW Bus Driver
Chelsea, AL
Http://www.moldhaus.com


On 1/10/2011 2:34 PM, Bill Merrill wrote:
> For figuring out how much water and plaster ( number 1 potters plaster) =
are needed to fill a specific space use the following formula. The followin=
g formula can be reduced or increased using the basic formula.
>
>
>
> For every 80 cubic inches of space you will need 1 quart of cool water a=
nd 2 =BE pounds of plaster. You may get by with 2 3/8 pounds of plaster, b=
ut I find 2 =BE pounds of plaster make a good density.
>
>
>
> Example: 8" x 10" X 1" =3D 80 cubic inches
>
>
>
> For every 80 cubic inches use: 1 quart of water and 2 =BE pounds of plas=
ter.
>
>
>
> Pour the plaster into the water by sifting . Let it set until the plast=
er is absorbed into the water. If you don't' stir it,
>
> it will not start setting up right away. Agitate the plaster and water =
with your hand underneath the surface of the mix. The plaster will stand =
up like frosting when you drag you finger over it, that is a good time to =
pour. Depending on the mold you are pouring into. Tap the bucket before yo=
u pour and also tap the mold after pouring to get rid of air bubbles.
>
>
>
> Hot water will accelerate the hardening process. Cool water will harden =
more slowly. I use luke- warm water.
>
>
>
>
>
>

John Rodgers on wed 12 jan 11

Mind you, I said spritz, not wash - the model/mold down with alcohol.
Perhaps it would have been best had I said "lightly mist" the model/mold
with alcohol. A spritz may be too much. This is one of those things
where experience tells you how much. In my experience a light misting
doesn't adversely affect the mold soap, and definitely enhances the
interface between the mold and the fresh plaster - breaking any trapped
bubbles and resulting in a very good mold surface.

As for alcohol on a clay model - unless you seal the surface with
shellac or urethane or other slick, waterproof material, it won't work
The mist of alcohol will just absorb right into the surface.

A trick that eases separation of the new plaster cast from the mold is
to wait until the plaster is set, and the heat of hydration has reached
full peak. At that point, the heat and the excess water from the process
softens the mold soap layer, and makes it more easy to separate. If you
wait until the new plaster cast is cool, the free water is re-absorbed,
and the soap hardens again, and it can be difficult to separate.

John

John Rodgers
Clayartist and Moldmaker
88'GL VW Bus Driver
Chelsea, AL
Http://www.moldhaus.com


On 1/11/2011 11:33 PM, David Martin Hershey wrote:
> Hi John,
>
> Thanks for the alcohol in the plaster tip.
> You mentioned this a few years back,
> and I've used it ever since. Works great!
>
> Re: spraying alcohol inside the mold,
> does it re-wet the mold soap?
> Or is the water in the alcohol not enough to do this.
>
> Also, does it have any effect on a leather hard clay original?
>
> Just had a D'oh! moment!
>
> I have a glaze that foams in the ball mill.
>
> I've tried anti foaming agent- didn't work.
> But never thought to try alcohol afterwords...
>
> Best, DMH
>
> David Martin Hershey
> DMH Studio + Design
> 2629 Manhattan Ave #137
> Hermosa Beach CA USA
> 90254-2447 424.241.3809
> http://www.dmhstudio.com/
> http://www.obamacardgold.com
> http://www.winetastingtrolley.com/
>
> On 1/10/2011 10:16 PM, John Rodgers wrote:
>> then just before pouring, spritz the surface
>> of the mold lightly with the alcohol. This will break any remaining
>> bubbles that may be trapped under the surface of the plaster that come
>> forth when the plaster is poured.
>
>

Alice DeLisle on thu 13 jan 11

John,
What kind of alcohol do you use?

Alice DeLisle

wanderland@att.net
http://www.etsy.com/shop/IslandTextures

John Rodgers on thu 13 jan 11

Denatured alcohol from any paint supply store. Even Walmart has it in
their paint section. I put it in a garden spray bottle

John

John Rodgers
Clayartist and Moldmaker
88'GL VW Bus Driver
Chelsea, AL
Http://www.moldhaus.com


On 1/13/2011 7:26 AM, Alice DeLisle wrote:
> John,
> What kind of alcohol do you use?
> Alice DeLisle
>
> wanderland@att.net
> http://www.etsy.com/shop/IslandTextures
>
>
>

C. Tullis on wed 13 apr 11

We're having a discussion in the studio here in Denver. What is the diff=
=3D
erence=3D20
between #1 Pottery plaster and Moulding plaster and how would they perfor=
=3D
m=3D20
differently in slip casting moulds.

Bill Merrill on sun 14 aug 11

People are still discussing plaster bats. I have used plaster bats on =3D
my Randall wheel since 1966. I had a Soldner P400 made last year with a =
=3D
tapered shaft to accept all my bucket and flat heads for my Randall =3D
wheel. Plaster is superior to plywood or Masonite or even the synthetic =
=3D
material bats. Plaster has the advantage over the other bats as plaster =
=3D
draws water from the base of the pot other bats don't do that, or at =3D
least the ones I have seen. The plaster bat stiffens the foot area of a =
=3D
pot and the top of the pot will be about the same leather hardness as =3D
the body and lip. You don' have to wait until the pot dries off the =3D
plaster bat. If you want you can trim the pot in it's upright position =3D
(like a pitcher) and the pop of the pot by using a thin scientific =3D
stainless steel spatula, rotating the wheel slowly and sliding the =3D
spatula under the base of the pop. It will come off easily. Because =3D
the base of the pot is leather hard you can still turn a pot upside down =
=3D
and trim it. =3D20

=3D20

I have 8", 12", 16" and 20" plaster bats that fit both of my wheels. I =3D
have never had a pot with any plaster pop outs in them in all the pieces =
=3D
I have made. Randall wheels are no longer being made but Dave Ball at =3D
Blue Bird Mfg. may start making bat molds and bucket style wheel heads. =
=3D
I also have an 18" aluminum flat wheel head thad I attach a large piece =3D
of plywood to if I want to make 30" or larger platters. The plywood =3D
attaches to the wheel head with bolts the are counter sunk into the =3D
plywood and are held on with wing nuts. I put down a circle of news =3D
paper in the canter of the plywood and then put on the clay. I pound it =
=3D
down with my fists and then throw the clay. The newspaper releases the =3D
clay from the plywood. I then use a spatula to go unf=3D3Dder the outside =
=3D
botton of the platter. I have also just put canvas on the plywood, made =
=3D
the platter and after it stiffened up some slid the canvas and platter =3D
off the plywood. VictorBabu makes very lrge porcelain platters and he =3D
uses large plaster bats. The Randall system can raise one's production =
=3D
speed.

=3D20

If you want to make plaster bats or use plaster in general, there is a =3D
formula that will help you mx your plaster so that you don't waste or =3D
under guess how much plaster you need. For example if you want to fill =3D
a 8"x 10" x 1" form that equals 80 cubic inches of plaster. For every =3D
80 cubic inches of plaster you need 1 quart of water and 2 =3DBE pounds of =
=3D
plaster. When mixin the plaster, measure out your water in a bucket and =
=3D
sift in the plaster. Let the plaster sit for a few minutes before you =3D
stir it with your hand. Letting the plaster absorb water before you =3D
stir it will help keep the plaster from getting lumps in it. After you =3D
stir it, let it sit until it becomes thicker. I don't pour plaster =3D
until when I drag my finger across the top of it the finger mark starts =3D
to stand up a little. I tap the bucket on the floor to get rid of air =3D
bubbles and then pour into a mold. For wedging tables I use Melamine to =
=3D
make the form. With a base of glass, Plexiglas or Melamine I coat it =3D
with mold release. The bottom of the wedging surface is the smooth like =
=3D
the surface it was poured on. I use temped water, cold water retards the =
=3D
setting up of the plaster and hot water doesn't give much working time. =
=3D
One of the better classes I took was a plaster class with Wally Higgins =3D
at Alfred ( in "73). He was one of the better teachers I have known. =3D20

=3D20

Attached are 3 calculation sites . They are great and easy to use. You =
=3D
can calculate grams to onces or pounds...all kinds of useful =3D
calculations.

=3D20

May all you endeavors be successful!!! Keep making pots, the best one =3D
are still in you!!!

=3D20

Bill

=3D20

http://www.onlineconversion.com/ GENERAL ON LINE CONVERSION SUITE

=3D20

http://www.online-calculators.co.uk/volumetric/cylindervolume.php =
=3D
VOLUME OF A CYLINDER

=3D20

http://www.online-calculators.co.uk/volumetric/cubevolume.php =3D
VOLUME OF A CUBE

=3D20

=3D20

=3D20

=3D20

=3D20

David Woof on mon 15 aug 11

O.M.G John=3D2C Hi Everyone=3D2C

I don't know what corner John has turned lately but to say as he has: <"and=
=3D
the whole "plaster=3D20
pop-outs in your clay" thing is bogus fear-mongering."> is just plain untru=
=3D
e!!!

John where do you come off from with a statement like that?!!! =3D20

I have experienced several shared studio school situations where someone ra=
=3D
n chips or chunks of=3D20
plaster bats or other plaster mold forms in the clay scraps through a pug m=
=3D
ill/mixer and=3D20
since the budget was "too tight" to just throw the contaminated clay out we=
=3D
concentrated=3D20
on big knarly sculptures for near two semesters before we could trust we
had used it up and worked it through the clay scrap.=3D20

Little bit of plaster in clay goes a long way. Pop outs can have time lag a=
=3D
nd=3D20
it is not good to find a fresh pop out chip lying on a pedestal opening nit=
=3D
e of a show.
=3DA0
My students used newly mixed clay for vessels of domestic utility.

******************************
"Lime pops" in pottery=3D2C occurring from a plaster source=3D2C is a physi=
cal =3D
reality=3D3B and asserting=3D20
it is not so is just as ignorant as losing pots to cracks after a first sem=
=3D
ester of study=3D20
with a good teacher. No matter which batts one uses.
*******************************

Have a blessed day=3D2C=3D20

David Woof.......Making pots in Clarkdale=3D2C Arizony...where all the cowg=
ir=3D
ls are lean and the=3D20
cowboys as wall eyed as an abused bronc. Yippie ki yo ki yaaaaa! Slap hide=
=3D
!!! We ride'n now!!!

How am I doin? Am I learnin the lingo? =3D20

Think I'll go out back an punch a cow=3D3B they's a eatin mi hollyhocks!!!
=3DA0
Maybe I better quit reading Clayart before I turn into a wall eyed potter!!=
=3D
!
_____________________________________________________=3D20

8.2. Re: Plaster
Posted by: "John Rodgers" inua@CHARTER.NET=3D20
Date: Mon Aug 15=3D2C 2011 9:51 am ((PDT))
=3D20
Bill=3D2C
I have used the Pure and Simple bat making system for years now. Like=3D20
you=3D2C I think plaster bats are great=3D2C and the whole "plaster pop-out=
s in=3D
=3D20
your clay" thing is bogus fear-mongering. You will lose more pots to=3D20
cracks than you ever might with a plaster pop-out from using a plaster=3D2=
0
bat - unless you are just so sloppy you might ought to being doing=3D20
something else besides doing pottery.
=3D20
The P&S system with it's key drive works for me.
=3D20
John
=3D20
John Rodgers
Clayartist and Moldmaker
88'GL VW Bus Driver
Chelsea=3D2C AL
Http://www.moldhaus.com
=3D20




=3D

John Rodgers on mon 15 aug 11

Bill,
I have used the Pure and Simple bat making system for years now. Like=3D20
you, I think plaster bats are great, and the whole "plaster pop-outs in=3D2=
0
your clay" thing is bogus fear-mongering. You will lose more pots to=3D20
cracks than you ever might with a plaster pop-out from using a plaster=3D2=
0
bat - unless you are just so sloppy you might ought to being doing=3D20
something else besides doing pottery.

The P&S system with it's key drive works for me.

John

John Rodgers
Clayartist and Moldmaker
88'GL VW Bus Driver
Chelsea, AL
Http://www.moldhaus.com


On 8/14/2011 11:21 PM, Bill Merrill wrote:
> People are still discussing plaster bats. I have used plaster bats on =
=3D
my Randall wheel since 1966. I had a Soldner P400 made last year with a =
=3D
tapered shaft to accept all my bucket and flat heads for my Randall wheel=
=3D
=3D2E Plaster is superior to plywood or Masonite or even the synthetic mat=
=3D
erial bats. Plaster has the advantage over the other bats as plaster dra=
=3D
ws water from the base of the pot other bats don't do that, or at least t=
=3D
he ones I have seen. The plaster bat stiffens the foot area of a pot and=
=3D
the top of the pot will be about the same leather hardness as the body a=
=3D
nd lip. You don' have to wait until the pot dries off the plaster bat. =
=3D
If you want you can trim the pot in it's upright position (like a pitcher=
=3D
) and the pop of the pot by using a thin scientific stainless steel spatu=
=3D
la, rotating the wheel slowly and sliding the spatula under the base of t=
=3D
he pop. It will come off easily. Because the base of the pot is leather=
=3D
hard you can still turn a pot upside down and trim it.
>
>
>
> I have 8", 12", 16" and 20" plaster bats that fit both of my wheels. I=
=3D
have never had a pot with any plaster pop outs in them in all the pieces=
=3D
I have made. Randall wheels are no longer being made but Dave Ball at B=
=3D
lue Bird Mfg. may start making bat molds and bucket style wheel heads. I=
=3D
also have an 18" aluminum flat wheel head thad I attach a large piece of=
=3D
plywood to if I want to make 30" or larger platters. The plywood attach=
=3D
es to the wheel head with bolts the are counter sunk into the plywood and=
=3D
are held on with wing nuts. I put down a circle of news paper in the ca=
=3D
nter of the plywood and then put on the clay. I pound it down with my fi=
=3D
sts and then throw the clay. The newspaper releases the clay from the pl=
=3D
ywood. I then use a spatula to go unf=3D3Dder the outside botton of the pl=
=3D
atter. I have also just put canvas on the plywood, made the platter and =
=3D
after it stiffened up some slid the canvas and platter off the plywood. =
=3D
VictorBabu makes very lrge porcelain platters and he uses large plaster =
=3D
bats. The Randall system can raise one's production speed.
>
>
>
> If you want to make plaster bats or use plaster in general, there is a =
=3D
formula that will help you mx your plaster so that you don't waste or und=
=3D
er guess how much plaster you need. For example if you want to fill a 8"=
=3D
x 10" x 1" form that equals 80 cubic inches of plaster. For every 80 cub=
=3D
ic inches of plaster you need 1 quart of water and 2 =3DBE pounds of plaste=
=3D
r. When mixin the plaster, measure out your water in a bucket and sift i=
=3D
n the plaster. Let the plaster sit for a few minutes before you stir it =
=3D
with your hand. Letting the plaster absorb water before you stir it will=
=3D
help keep the plaster from getting lumps in it. After you stir it, let =
=3D
it sit until it becomes thicker. I don't pour plaster until when I drag =
=3D
my finger across the top of it the finger mark starts to stand up a littl=
=3D
e. I tap the bucket on the floor to get rid of air bubbles and then pour=
=3D
into a mold. For wedging tables I use Melamine to make the form. With =
=3D
a base of glass, Plexiglas or Melamine I coat it with mold release. The =
=3D
bottom of the wedging surface is the smooth like the surface it was poure=
=3D
d on. I use temped water, cold water retards the setting up of the plaste=
=3D
r and hot water doesn't give much working time. One of the better classe=
=3D
s I took was a plaster class with Wally Higgins at Alfred ( in "73). He =
=3D
was one of the better teachers I have known.
>
>
>
> Attached are 3 calculation sites . They are great and easy to use. Yo=
=3D
u can calculate grams to onces or pounds...all kinds of useful calculatio=
=3D
ns.
>
>
>
> May all you endeavors be successful!!! Keep making pots, the best one=
=3D
are still in you!!!
>
>
>
> Bill
>
>
>
> http://www.onlineconversion.com/ GENERAL ON LINE CONVERSION SUITE
>
>
>
> http://www.online-calculators.co.uk/volumetric/cylindervolume.php =
=3D
VOLUME OF A CYLINDER
>
>
>
> http://www.online-calculators.co.uk/volumetric/cubevolume.php V=
=3D
OLUME OF A CUBE
>
>
>
>
>
>
>
>
>
>
>
>

Vince Pitelka on mon 15 aug 11

Bill Merrill wrote:
"People are still discussing plaster bats. I have used plaster bats . . .
since 1966. . . . Plaster is superior to plywood or Masonite or even the
synthetic material bats. Plaster has the advantage over the other bats as
plaster draws water from the base of the pot other bats don't do that, or a=
t
least the ones I have seen. The plaster bat stiffens the foot area of a po=
t
and the top of the pot will be about the same leather hardness as the body
and lip. You don' have to wait until the pot dries off the plaster bat. I=
f
you want you can trim the pot in it's upright position (like a pitcher) and
the pop of the pot by using a thin scientific stainless steel spatula,
rotating the wheel slowly and sliding the spatula under the base of the pop=
.
It will come off easily. Because the base of the pot is leather hard you
can still turn a pot upside down and trim it."

Bill -
When speaking of bats in general terms, plaster is not superior to other
materials, and other materials are not superior to plaster. It all depends
on what kind of system works best for you. I have been professionally
involved in ceramics for almost as long as you, and I have never liked
plaster bats. I do not like the fact that they pull moisture out of the
bottom of the pot. I want to control that myself. I do not like the
vulnerability of plaster and the possibilities of contamination in the clay=
.
I do not like the fact that they take so long to dry off after use.

I find plastic bats too slick and too flexible. I find Masonite too
flexible, and it is very difficult to get true double-tempered Masonite
anymore. I have never found a bat materials that I find superior to 1/2"
Medex waterproof MDF, a product of SierraPine.

Plaster bats are especially challenging in any institutional studio, becaus=
e
they are bulky, heavy, and they chip so easily and introduce small particle=
s
into the clay, causing lime pops later on.

I certainly am not opposed to the use of plaster bats on general principle,
and I know that lot of people love them, but in terms of performance,
durability, ease of handling, and required storage space, I prefer Medex
bats over all other types. In my book I have instructions for making bats
from various materials including Medex and plaster, but I do express my
preference for Medex.
- Vince

Vince Pitelka
Appalachian Center for Craft
Tennessee Tech University
vpitelka@dtccom.net; wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka

Carl Cravens on tue 16 aug 11

The message I'm getting here is that if you work more our less alone, plast=
=3D
er is fine. But of you work in an "open" studio setting (class room, etc), =
=3D
you can't count on everyone handling plaster bats properly to avoid problem=
=3D
s.

It seems that these two groups are talking past each other here to some=3D
extent.

Ric Swenson on tue 16 aug 11

Lime pops happen when plaster invades the body....it might be later....but =
it happens. Keep all plaster out of the studio as much as you can...

cause...shit happens.

moisture makes the plaster expand in time....years later...or in a few mont=
hs....

I have noticed a few lime pops in my new batts...of saggar clay...but no p=
roblem in batts. a divot or two. cover with clay. and at 1.60 $ per batt=
...who cares?

Clay here is cheap....as I mentioned before. between 7-12 RMB 52 cents t=
o $1.92 per 50 lb slug. the best clay costs a bit more..very pure porcelai=
n.



as white as the porcelana beach shell from Portugal...from hence the Engli=
sh name. Porcelain.



ric



Richard H. ("Ric") Swenson, Teacher,
Office of International Cooperation and Exchange of Jingdezhen Ceramic Inst=
itute,
TaoYang Road, Eastern Suburb, Jingdezhen City.
JiangXi Province, P.R. of China.
Postal code 333001.


Mobile/cellular phone : 86 13767818872


< RicSwenson0823@hotmail.com>




> Date: Mon, 15 Aug 2011 19:34:45 -0600
> From: woofpots@HOTMAIL.COM
> Subject: Re: Plaster
> To: Clayart@LSV.CERAMICS.ORG
>
> O.M.G John, Hi Everyone,
>
> I don't know what corner John has turned lately but to say as he has: <"a=
nd the whole "plaster
> pop-outs in your clay" thing is bogus fear-mongering."> is just plain unt=
rue!!!
>
> John where do you come off from with a statement like that?!!!
>
> I have experienced several shared studio school situations where someone =
ran chips or chunks of
> plaster bats or other plaster mold forms in the clay scraps through a pug=
mill/mixer and
> since the budget was "too tight" to just throw the contaminated clay out =
we concentrated
> on big knarly sculptures for near two semesters before we could trust we
> had used it up and worked it through the clay scrap.
>
> Little bit of plaster in clay goes a long way. Pop outs can have time lag=
and
> it is not good to find a fresh pop out chip lying on a pedestal opening n=
ite of a show.
>
> My students used newly mixed clay for vessels of domestic utility.
>
> ******************************
> "Lime pops" in pottery, occurring from a plaster source, is a physical re=
ality; and asserting
> it is not so is just as ignorant as losing pots to cracks after a first s=
emester of study
> with a good teacher. No matter which batts one uses.
> *******************************
>
> Have a blessed day,
>
> David Woof.......Making pots in Clarkdale, Arizony...where all the cowgir=
ls are lean and the
> cowboys as wall eyed as an abused bronc. Yippie ki yo ki yaaaaa! Slap hid=
e!!! We ride'n now!!!
>
> How am I doin? Am I learnin the lingo?
>
> Think I'll go out back an punch a cow; they's a eatin mi hollyhocks!!!
>
> Maybe I better quit reading Clayart before I turn into a wall eyed potter=
!!!
> _____________________________________________________
>
> 8.2. Re: Plaster
> Posted by: "John Rodgers" inua@CHARTER.NET
> Date: Mon Aug 15, 2011 9:51 am ((PDT))
>
> Bill,
> I have used the Pure and Simple bat making system for years now. Like
> you, I think plaster bats are great, and the whole "plaster pop-outs in
> your clay" thing is bogus fear-mongering. You will lose more pots to
> cracks than you ever might with a plaster pop-out from using a plaster
> bat - unless you are just so sloppy you might ought to being doing
> something else besides doing pottery.
>
> The P&S system with it's key drive works for me.
>
> John
>
> John Rodgers
> Clayartist and Moldmaker
> 88'GL VW Bus Driver
> Chelsea, AL
> Http://www.moldhaus.com
>
>
>
>
>
>

John Rodgers on tue 16 aug 11

From years of hands on experience. Keep your place clean, pay
attention to your work, take care of your equipment, and you won't have
troubles with plaster.

John

John Rodgers
Clayartist and Moldmaker
88'GL VW Bus Driver
Chelsea, AL
Http://www.moldhaus.com


On 8/15/2011 8:34 PM, David Woof wrote:
> John where do you come off from with a statement like that?!!!

Taylor Hendrix on wed 17 aug 11

Welcome to the Ram's Head Pub, Carl, a place where everyone is allowed
to talk past each other at will.

Some of us are just too sloppy in our potting habits to pull off
plaster bats no matter how alone we work.

And some of us teach very well behaved, clean classes of students who
use plaster bats with impunity.

This is what makes the RH such an entertaining place to have a drink.

Taylor, in Rockport TX
wirerabbit1 on Skype (-0600 UTC)
http://wirerabbit.blogspot.com
http://wirerabbitpots.blogspot.com
http://www.flickr.com/photos/wirerabbit/



On Tue, Aug 16, 2011 at 9:01 PM, Carl Cravens wrote:
> The message I'm getting here is that if you work more our less alone, pla=
ster is fine. But of you work in an "open" studio setting (class room, etc)=
, you can't count on everyone handling plaster bats properly to avoid probl=
ems.
>
> It seems that these two groups are talking past each other here to some e=
xtent.
>

John Rodgers on wed 17 aug 11

Prol'ly. I don't have an open studio. Nobody but me to screw it up.
Less troubles that way. The minute you add people, something will go
wrong, something will get messed up - guaranteed.

John

John Rodgers
Clayartist and Moldmaker
88'GL VW Bus Driver
Chelsea, AL
Http://www.moldhaus.com


On 8/16/2011 9:01 PM, Carl Cravens wrote:
> It seems that these two groups are talking past each other here to some e=
xtent.

James A. Monk on wed 17 aug 11

-----Original Message-----
From: Clayart [mailto:Clayart@LSV.CERAMICS.ORG] On Behalf Of Carl =3D
Cravens

The message I'm getting here is that if you work more our less alone, =3D
plaster is fine. But of you work in an "open" studio setting (class =3D
room, etc), you can't count on everyone handling plaster bats properly =3D
to avoid problems.

It seems that these two groups are talking past each other here to some =3D
extent.




Carl,=3D20

I agree with you.=3D20

When I was asked to post the method, that I use to make my own plaster =3D
bats, I did not mean to start a onward discussion of the problems that =3D
people have with the different materials that the different bats are =3D
made from.=3D20

I misunderstood, a question that was asked by a list member, about a =3D
"bat grabber." I offered to give my method of making plaster bat off =3D
list. I receive a request from another list member to post it here on =3D
Clay Art. I did has I was asked.

I have had experience with both plaster and textured plastic bats. I do =3D
not like the plastic, because, when you undercut the pot, it has the =3D
tendency to stick to the plastic after the pot is cut off of the bat and =
=3D
left there to reach the stage that one can trim the pot and add what =3D
every decoration that one may want on the pot. The only bad experience, =3D
that I have had with plaster bats, is that when you drop them they tend =3D
to chip or break into, especially if they or old.

James

Mike Gordon on wed 17 aug 11

Starting in 1959, at the California College Of Arts & Crafts, we had
plaster bats only, plaster wedging tables, & 5 classes a week + night
classes. No problems. I taught ceramics for 30 yrs. in college & high
school using only plaster bats & plaster wedging tables, no problems.
It isn't hard to use successfully in a class room setting if you're are
careful & diligent about it's use, just as you would be about clay dust
& glaze chemicals. Mike Gordon

Bill Merrill on fri 24 feb 12

If you are interested in plaster for molds, bats, etc. look for a
workshop with Tom Spleth. He was a student in the late 60's/early 70's
of Wally Higgins at Alfred. He gives a great workshop.

As a point of reference: =3D20

For every 80 cubic inches of finished plaster you need ..(.example 8" x
10" x 1" =3D3D 80 cubic inches ) you will need 1 quart of water and 2 3/4
pounds of plaster. If you want a harder denser plaster mix, use 3
pounds of plaster for every quart of water. I use # 1 potters plaster.
=3D20
Put your water in your mixing bucket. Use lukewarm water. Cold water
retards the setting time and , hot water is not recommended as there is
no working time. Add the plaster by sifting the plaster into the water
with your hand until the plaster is absorbed into the water. DO NOT
STIR for several minutes. Give the plaster a chance to absorb the
water. Stir the plaster by agitating your hand under the surface of the
mix. The plaster will become thoroughly mixed this way. The stirring
will start the mix to go through its chemical change. Tap the bucket up
and down to get rid of air bubbles, they will come to the surface. Drag
your finger across the mix. If the mix peaks a little without settling
down totally , this is a good time to pour. Pouring too thin will allow
the plaster/water mix to potentially to run out of seams in your mold.
Don't forget to put a mold release on the walls/bottom of your form so
the plaster will release. If building a flat angled mold I use
Melamine, a product that has a Formica like surface on one side. The
plaster releases easily .When the plaster starts going through the
heating stage of setting up, wait a few minutes and release The screws,
rubber bands whatever is holding the form together. This will keep the
mold from developing any cracks at joints due to expansion of plaster
when going through the hardening stage. During the heat stage the
plaster is weak and the mold should not be taken off until the plaster
has gone through the curing process( after the heat has dissipated from
the mold. Plaster is weak up to that point.
Make a batch large enough to make 1 pour. I have several 30" by 30" x
3" wedging areas.
=3D20
30" x 30" x 3" =3D3D 2700 2700 divided by 80 =3D3D33.75 quarts of water.
2.75 lbs plaster X 33.75 quarts of water + 92.8 pounds of plaster.
=3D20
If you have not poured plaster before this amount is not advise without
help. Make a 4" x 4" x 4" open cube. use mold release and figure your
plaster and water amounts. Pour the form. When the plaster use
something like a metal straight edge to take off any extra plaster. =3D20
=3D20
If making a wedging table, for the forms use Melamine so the bottom and
sides of the mold are perfectly smooth. I have aluminum molds for my
plaster bats. I use Plexiglas for the molds to set on, so a extremely
smooth surface is achieved on the throwing side of the bat. These molds
are made to be poured upside down from the way they will be used on the
bucket heads for my wheels. I have 8", 12", 16" and 20" plaster bats.
For large platters I have an 18" aluminum flat wheel head and I bolt
large circular pieces of plywood to the flat head for platters over 30"
in diameter.

Bill Merrill

Robert Harris on fri 23 mar 12

When I was at high school (in the late 80's) we had asbestos-cement
bats. The asbestos fibres were there as a strengthener - think cement
based fibreglass.

They were the best bats I have ever used. Thin but dense (maybe 3/16")
they never warped, the holes never got bigger and, like with plaster,
the bottoms of the pots dried at a similar rate to the rest of the pot
(at least if they were covered slightly).

I currently throw mugs and bowls and other small things on bisqued
tiles (6" square) for the same reason. I just cut a tile shaped hole
in a plastic bat and it works fine. If the tile is a little loose just
stick a gob of clay down the wobbly edge. Again the bottoms of the
pots dry and just naturally pull up off the tile when they're ready to
be turned.

These days there are a number of different plasters and gypsum cements
available, many of which are pretty resistant to chipping etc - no
need to use "Pottery Plaster No. 1", especially for throwing bats
where you are not hugely interested in the water absorbancy aspect.

I wish I could find some replacement for the asbestos fibres though,
they really made a difference.

Robert


On Fri, Mar 23, 2012 at 5:44 PM, Bill Merrill wrote:
> I don't understand why people are so down on plaster and plaster bats.
> I have been using plaster bats on one of my Randall wheels since3 1967.
> I also have a Soldner P400 that I had the shaft tapered to fit all of
> bucket and flat heads from the Randall bat system.
> I have 8", 12" 16' and 20 inch plaster bats. =3DA0For large platters I us=
e
> plywood bolted to an 18" flat head.
>
> I have also used plaster bats in a college situation since 1970.
> Students are respectful of the bats. =3DA0If they want plaster bats I hav=
e
> molds that the student uses to pour their bats. =3DA0I also have Mexdex b=
at=3D
s
> ( recommended to me by Vince Pilteka) and they are very good also. =3DA0I
> like the plaster bats as the bottom of the pots stiffen up slightly to
> match the rest of the pots when in the drying to a leather hard state.
> For trimming of pitchers etc. the pot can stay on the wheel and =3DA0the =
po=3D
t
> can be removed from the bat by sliding a thin sharpened scientific
> stainless spatula under the base and the pot and the pot comes off the
> bat with a smooth bottom.
>
> The nice thing about the Randall bucket head system is that a pot can be
> removed and let stiffen u if you want and then put the pot/bat back on
> the bucket head and it is perfectly centered.
>
> The small plaster bats take up little studio space. =3DA0The bats can be
> easily stacked and if space is a problem, =3DA0use the Medex bats.
>
> Dave Shaner, Val Cushing, Ken Ferguson , Victor Babu and many other
> potters used plaster bats all of their careers.
>
> As for plaster in clay, why throw it out. =3DA0Use it for making pieces t=
ha=3D
t
> you would make molds of for hand-building. =3DA0It still may be good for
> bisque molds.
>
> If you don't Want plaster, then it's very simple...don't use plaster,
> just like if you don't like Mozart, don't listen to Mozart...
>
> Bill



--=3D20
----------------------------------------------------------

Bill Merrill on fri 23 mar 12

I don't understand why people are so down on plaster and plaster bats.
I have been using plaster bats on one of my Randall wheels since3 1967.
I also have a Soldner P400 that I had the shaft tapered to fit all of
bucket and flat heads from the Randall bat system. =3D20
I have 8", 12" 16' and 20 inch plaster bats. For large platters I use
plywood bolted to an 18" flat head. =3D20

I have also used plaster bats in a college situation since 1970.
Students are respectful of the bats. If they want plaster bats I have
molds that the student uses to pour their bats. I also have Mexdex bats
( recommended to me by Vince Pilteka) and they are very good also. I
like the plaster bats as the bottom of the pots stiffen up slightly to
match the rest of the pots when in the drying to a leather hard state.
For trimming of pitchers etc. the pot can stay on the wheel and the pot
can be removed from the bat by sliding a thin sharpened scientific
stainless spatula under the base and the pot and the pot comes off the
bat with a smooth bottom.=3D20

The nice thing about the Randall bucket head system is that a pot can be
removed and let stiffen u if you want and then put the pot/bat back on
the bucket head and it is perfectly centered.=3D20

The small plaster bats take up little studio space. The bats can be
easily stacked and if space is a problem, use the Medex bats.

Dave Shaner, Val Cushing, Ken Ferguson , Victor Babu and many other
potters used plaster bats all of their careers.

As for plaster in clay, why throw it out. Use it for making pieces that
you would make molds of for hand-building. It still may be good for
bisque molds.

If you don't Want plaster, then it's very simple...don't use plaster,
just like if you don't like Mozart, don't listen to Mozart...

Bill

John Britt on sat 24 mar 12

Love plaster bats. And they make life a lot easier:

http://www.youtube.com/watch?v=3D3D_GfdPDg3VVE

Johnbrittpottery.com

Pottery by John on sat 24 mar 12

On 3/23/2012 7:50 PM, Robert Harris wrote:
> I wish I could find some replacement for the asbestos fibres though,
> they really made a difference.


I wonder if the fibers that are used for concrete would work. There are
synthetic fibers and steel fibers. They can be found at home improvement
and concrete specialty stores.

The Hardi line of board products use wood fiber with cement, but the
surface of the products I have found are not smooth like a plaster bat.
I like throwing directly on the wheelhead and use pieces of 1/4-inch
Hardi Backer to put pots on to dry. The bottoms dry along with the rest
of the pot (you can see and feel the damp spot under the pot), but I
usually turn pots bottoms up after a day of drying on the Hardi Backer.

--
John Lowes
Sandy Springs, Georgia, USA
http://wynhillpottery.weebly.com

Snail Scott on sat 24 mar 12

On Mar 23, 2012, at 6:50 PM, Robert Harris wrote:

> When I was at high school (in the late 80's) we had asbestos-cement
> bats. The asbestos fibres were there as a strengthener - think cement
> based fibreglass...


A lot of areas have houses with cement/asbestos
siding - durable and fireproof. There's no hazard
since the asbestos is locked into the solid shingles,
but it's still illegal to dispose of the stuff in the trash,
so every time someone wants to re-do their siding,
they either just cover it over, or stack the old shingles
on the sidewalk. They will be gone the next day,
taken by people who need to replace a few on their
own house, or by handymen or remodelers who
have regular need of the stuff for repairs. If you know
anyone who lives in one of these neighborhoods,
you could probably get some pretty easily. It's about
1/4" thick, about 12"x18", and though it has fake wood
texture on one side, the backs are smooth. Just cut it
wet if you want to avoid dust.

-Snail

Mike Gordon on sat 24 mar 12

I agree with John Britt about plaster bats, we used them in the 60's at
the College of Arts & Crafts in Oakland, Ca. now called College of the
Arts, & I've used them for 40 + years in my own studio. I have never
had a problem with using plaster. I don't think "plasti bats" had been
invented yet when I was in college. Mike Gordon

Ric Swenson on sun 25 mar 12

Mike, John and all of you out there in clayland.....

I guess I have used every imaginable material for batts. I the 60s At PLU =
we used pot lifters ( not my favorite- by any means) At UAA we used plaste=
r batts we made from #1 pottery plaster in pie tins. In my own studio I us=
ed masonite batts...painted edges and never got them too wet. I used cemen=
t board too...but it is correct to wear breathing mask to prevent the dust =
from lungs...and cut outside the studio. For larger pieces, while in Benni=
ngton, I found formica sink cutouts for free....treated the particle board=
with varnish perodically....but the formica lasted a LONG time. In China =
I have found stoneware clay batts made from saggar clay...fired to cone 8 o=
r so...have to shop for the really flat ones available in the shop that mak=
es them. Have also used Vermont slate shingles, plywood, kiln shelves, ro=
und plastic cutting boards, etc.

The best was the plaster...easily adhered to the wheel head with H2O ... e=
asy to release and they suck the moisture from the foot....(watch for chips=
of plaster of course...lime popping is not a good thing.)

BEST...IMHO


best,


Ric





-----------------


Ric Swenson, B.F.A, M.F.A.
Ceramist, Artist and Teacher.
Jing De Zhen Ceramic Institute
Jing De Zhen City,
Jiang Xi Province
China
Mobile: 86-13767818872



> Date: Sat, 24 Mar 2012 11:33:13 -0700
> From: clayart@EARTHLINK.NET
> Subject: Plaster
> To: Clayart@LSV.CERAMICS.ORG
>
> I agree with John Britt about plaster bats, we used them in the 60's at
> the College of Arts & Crafts in Oakland, Ca. now called College of the
> Arts, & I've used them for 40 + years in my own studio. I have never
> had a problem with using plaster. I don't think "plasti bats" had been
> invented yet when I was in college. Mike Gordon