Stephani Stephenson on thu 9 nov 06
Hi Paulette,
my first and most emphatic advice is , do not rely on the island
technique for mixing plaster!
people get use to it for their own purposes , but it is a highly
inaccurate way to mix plaster and going half and half with different
plasters doesn't make it any better!!!
If you haven't already done so, read "Mold making for the Ceramics" by
Donald Frith.
It is a fabulously informative book, plus it comes with a plaster
mixing guide.. And to the folks who tell you to 'mix half and half and
use the island method...tell them about the book too....
OK, I have a couple of questions regarding your questions.:)
Question #1. you said: "Recently I have heard from two people who
use tile presses (2- ton
types)", that they prepare the molds by combining #1 pottery plaster
and hydrocal or hydrostone. In one case the prep was done using
50:50 mixture by volume and employing the island technique. In the
other case, a percentage of pottery plaster to hydrostone was weighed
out, dry mixed with a ribbon mixer (?), and then prepared via the
weight or quantitative approach.
My question to you : are these hydraulic presses or simple mechanical
presses?,( i.e., no water, no air moving internally through the plaster
during release)
Either way, you do not need a ribbon mixer. You do need a good drill
and mixing atttachment or other mixer that can run for at least 8
minutes without burning out.
Paulette wrote: "According to each of these people, the molds were
harder (able to
withstand the pressure from the tile presses without breaking, but
still absorbent, and could still be carved right away, before they
cured."
My Question, OK I don't quite get your question...
Maybe I am just not reading the question correctly ...the question
initially reads as if carving is taking place after pressing. ?????But
that doesn't make sense to me.
Are you making a plaster model and taking a plaster mold from a plaster
model, or simply carving into the plaster mold itself, and using that
same mold later for pressing.???
Paulette wrote: "Does anyone prepare molds of a mixture of pottery
plaster and
hydrostone/hydrocal/ceramical. Can the plaster and gypsum cement be
mixed well in a low tech way without the aid of a ribbon cutter, and
still produce good molds without "swirling", or incomplete mixing of
the dry ingredients? Can this be done with the weight to weight
method (quantitative), rather than the island technique?"
My answers:
yes it is done. yes, a drill type mixer will do .TRead up on the
correct time to allow for slaking and mixing.
Most people under mix because they are afraid the plaster will go off
too soon.
This problem can be averted by proper mixing and using fresh
plaster/gypsum cement.
Weight method is always better than island method, even if you are
somewhat ballparking the consistency and math when you mix the 2
types, the only way you can repeat successful mixing is if you measure
the ingredients in a consistent manner!
My only other suggestion might be that there are lots of options on
the spectrum between pottery plaster and hydrostone.
hydrocal makes very serviceable press molds and is not limited to use
in purge molds.
duramold is a type of plaster that has fibers... I haven't carved it
but the fibers don't seem to be noticeable at all.it is soft like
pottery plaster, has a wee bit lower consistency (60) and also
absorbent, but holds up better in pressing.
the reason I asked if you are carving into the mold itself vs a model
is that you could use a softer plaster for the model , carve it , then
use a harder gypsum cement for the pressing mold.
happy tilemaking!
Stephani Stephenson
steph@revivaltileworks.com
http://www.revivaltileworks.com
John Rodgers on thu 9 nov 06
users
Paulette,
I don't know about these particular mixes, but I have done a lot of mold
making using #1 Pottery Plaster, Ultracal 30, Hydrostone and Hydrocal.
Never saw a need for dry mixing. I have always used either a high
quality steel paint mixer, or a stainless steel basket mixer from one of
the many pottery supply houses. This latter comes in different sizes and
has a basket made up of two vertical blades, two horizontal blades, and
two rings to tie them together. The blades have a pitch to them that
really throws the plaster when mixing. It gives the most thorough mix of
all.
I would think that given how thorough the basket type mixer will mix,
there should be no need to dry mix before adding to water, particularly
since hydrocal and ultracal have longer periods before setting begins.
Regards,
John Rodgers
Chelsea, Al
Paulette Carr wrote:
> Recently I have heard from two people who use tile presses (2- ton
> types), that they prepare the molds by combining #1 pottery plaster
> and hydrocal or hydrostone. In one case the prep was done using
> 50:50 mixture by volume and employing the island technique. In the
> other case, a percentage of pottery plaster to hydrostone was weighed
> out, dry mixed with a ribbon mixer (?), and then prepared via the
> weight or quantitative approach.
>
> According to each of these people, the molds were harder (able to
> withstand the pressure from the tile presses without breaking, but
> still absorbent, and could still be carved right away, before they
> cured.
>
> Does anyone prepare molds of a mixture of pottery plaster and
> hydrostone/hydrocal/ceramical. Can the plaster and gypsum cement be
> mixed well in a low tech way without the aid of a ribbon cutter, and
> still produce good molds without "swirling", or incomplete mixing of
> the dry ingredients? Can this be done with the weight to weight
> method (quantitative), rather than the island technique?
>
> The advantage to making a mold that is slightly (to more) durable
> than straight plaster, carve-able, and that will release without
> purging is very intriguing!
>
> Thanks, in advance for any information!
>
> My best,
> Paulette Carr
>
> Paulette Carr Studio
> Member/Potters Council
> St. Louis, MO
>
> ______________________________________________________________________________
>
> 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.
>
>
Paulette Carr on fri 10 nov 06
users
Hi, Stephani!
I do not use the island method, but rather the weight or quantitative
method. I was just trying to convert what I heard to what I could
do. The reason: I am using a clay body containing a great deal of
grog, and wanted a harder/more durable mold.
I did try your suggestion of casting a mold of the tile in ceramical,
and then trying the release via compressed air. I did not get a good
or rapid release, and though I could not spot any obvious undercuts.
The process was taking over 20 minutes, and the tile was hanging up.
At this point, the corners were drying, and the tile was warping...
I have been very successful using molds made of #1 pottery plaster,
and when (rare) there appeared to be a slight undercut, I could
adjust it by carving/sanding. As you know, this is not possible with
the ceramical.
I have read Frith's book (among several), and I do agree that it is
outstanding. It does not contain, however, any discussion on mixing
plaster with gypsum cement (hydrocal/hydrostone/ceramical). As I
said to someone earlier, this is a horse of a slightly different
color, but wouldn't it be wonderful to make a very durable mold that
is still absorbent??? In this case, small release problems could be
corrected, and the mold would still stand up to a small mechanical
tile press (2-ton), and/or more pressings.
To answer your questions:
(1) The tile presses in question are mechanical 2-ton tile presses,
which have been known to break molds of #1 pottery plaster. Both of
the people with whom I spoke used a mixture of #1 pottery plaster and
hydrocal/hydrostone to prevent the mold breakage. I am content to
press by hand, but want the durability of a harder mold so that I can
get more presses/mold before I lose detail.
(2) I do not specifically intend to carve afterwards, but if I see a
small problem area, I can fix it. I do try to be very careful about
undercuts, but sometimes even the smallest irregularity, presents a
release problem. The ability to carve is just a safety net.
(3) I do use a drill-type mixer - the SuperSafe Vortex mixer,
apparently designed by Donald Frith of the book fame. I have a
larger, turbo mixer for larger batches, which I seldom need.
With regard to ballparking the consistency, I could solve an
algebraic equation for the correct amount of water and average
consistency, depending upon the mixture I decide to try. BUT, how do
I know what the correct time for slaking and mixing is with a mixture
of plater and gypsum cement??? I am not certain what the slaking and
mixing times would be, and I wonder if the setup time functions
"algebraically", or if it would be better to go with the shorter
slaking and mixing of #1 Pottery plaster. A few experiments will
tell, I am sure. I think that the differential in set-up times could
cause inhomogeneities in the mold if the mixing was not adequate. I
am sure that is why the ribbon cutter for dry mixing was used - to
make certain that the powders were so well mixed that the resulting
"plaster" produced a homogeneous mixture and mold.
Reinventing the wheel seems to be my modus operandi. I was just
wondering if someone had already done this... or if there is any
literature about this.
I might like to try some of the other plaster types, such as
Duramold, but no one around here carries it. The costs of shipping
are prohibitive. My local distributor carries #1 pottery plaster and
hydrostone.
In the meantime, I am casting mother molds of #1 pottery plaster, and
then creating daughter molds for the tiles. If they wear out or
crack, I can just make a new daughter mold.
I am always looking for a better way. It is worth asking, and trying!
Many thanks, and happy tilemaking to you, too!
Paulette Carr
Paulette Carr Studio
Member/Potters Council
St. Louis, MO
Paulette Carr on fri 10 nov 06
users
John,
I do use a drill-type mixer - the SuperSafe Vortex mixer, apparently
designed by Donald Frith, and a larger, turbo mixer for larger
batches, which I seldom need. The jiffy mixer with two baskets is
for making larger volumes of plaster than I require, though I might
be able to stretch it. I would think that the turbo mixer would work.
I am still faced with determining how much time to slake and how much
time to mix with the blends. A good set of experiments may answer
the question. An interesting solution often presents more problems
to solve...
Many thanks!
Paulette Carr
Paulette Carr Studio
Member/Potters Council
St. Louis, MO
Date: Thu, 9 Nov 2006 19:25:24 -0600
From: John Rodgers
Subject: Re: Plaster molds for use in tile presses - question for
experts and
users
Paulette,
I don't know about these particular mixes, but I have done a lot of mold
making using #1 Pottery Plaster, Ultracal 30, Hydrostone and Hydrocal.
Never saw a need for dry mixing. I have always used either a high
quality steel paint mixer, or a stainless steel basket mixer from one of
the many pottery supply houses. This latter comes in different sizes and
has a basket made up of two vertical blades, two horizontal blades, and
two rings to tie them together. The blades have a pitch to them that
really throws the plaster when mixing. It gives the most thorough mix of
all.
I would think that given how thorough the basket type mixer will mix,
there should be no need to dry mix before adding to water, particularly
since hydrocal and ultracal have longer periods before setting begins.
Regards,
John Rodgers
Chelsea, Al
Susan P on fri 10 nov 06
users
Have read about using a different, but unspecified type of plaster for
press molds. Is this one way to acheive the same result?
On 11/9/06, John Rodgers wrote:
> Paulette,
>
> I don't know about these particular mixes, but I have done a lot of mold
> making using #1 Pottery Plaster, Ultracal 30, Hydrostone and Hydrocal.
> Never saw a need for dry mixing. I have always used either a high
> quality steel paint mixer, or a stainless steel basket mixer from one of
> the many pottery supply houses. This latter comes in different sizes and
> has a basket made up of two vertical blades, two horizontal blades, and
> two rings to tie them together. The blades have a pitch to them that
> really throws the plaster when mixing. It gives the most thorough mix of
> all.
>
> I would think that given how thorough the basket type mixer will mix,
> there should be no need to dry mix before adding to water, particularly
> since hydrocal and ultracal have longer periods before setting begins.
>
> Regards,
>
> John Rodgers
> Chelsea, Al
>
> Paulette Carr wrote:
> > Recently I have heard from two people who use tile presses (2- ton
> > types), that they prepare the molds by combining #1 pottery plaster
> > and hydrocal or hydrostone. In one case the prep was done using
> > 50:50 mixture by volume and employing the island technique. In the
> > other case, a percentage of pottery plaster to hydrostone was weighed
> > out, dry mixed with a ribbon mixer (?), and then prepared via the
> > weight or quantitative approach.
> >
> > According to each of these people, the molds were harder (able to
> > withstand the pressure from the tile presses without breaking, but
> > still absorbent, and could still be carved right away, before they
> > cured.
> >
> > Does anyone prepare molds of a mixture of pottery plaster and
> > hydrostone/hydrocal/ceramical. Can the plaster and gypsum cement be
> > mixed well in a low tech way without the aid of a ribbon cutter, and
> > still produce good molds without "swirling", or incomplete mixing of
> > the dry ingredients? Can this be done with the weight to weight
> > method (quantitative), rather than the island technique?
> >
> > The advantage to making a mold that is slightly (to more) durable
> > than straight plaster, carve-able, and that will release without
> > purging is very intriguing!
> >
> > Thanks, in advance for any information!
> >
> > My best,
> > Paulette Carr
> >
> > Paulette Carr Studio
> > Member/Potters Council
> > St. Louis, MO
> >
> > ______________________________________________________________________________
> >
> > 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.
> >
> >
>
> ______________________________________________________________________________
> 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.
>
Stephani Stephenson on fri 10 nov 06
users
Hi Paulette
It is often difficult to guage the experience level which lies behind
the question asked in a post.
so sometimes advice is given which will hopefully be useful to a
beginner, but which may
inadvertently undershoot the level of someone with experience.
and sometimes it difficult to read the question behind the question..
how broad or narrow the query is.
thank you for clarifying your process!
it helps to understand where the ,ah, crux or focus of the question
is.
and
from your latest post ah I see you have a good deal of experience in
the field!
good luck in your experiments and I hope you share your findings!
The people I knew who mixed their plasters did so in a fairly
idiosynchratic way...
much the same way you describe...
so their methods, as you point out are difficult to pass on and it
often up to the individual to do some research.
and it sounds like this may be one of those!
the main point is..to measure and take notes, which it sounds like you
do very well and I am sure you are savvy enough to figure out some
rations and
run some experiments. much like glaze testing. And I do mean it when I
say, your findings will have value for others.
I think , with a lot of this, we all are researchers, as well as
creators ,as well as producers
with all the written material there are enormous gray areas, uncharted
areas.
One difficulty with plaster, as you say , is availablity.
Another is quantity. it usually involves ordering 100 pound bags. and
when you mix the stuff, you need a bag of each, 2 bags,
which, unless you are making a lot of molds, can go bad on you.
Availability, quantity, weight, are all all common problems faced by
moldmakers. and supply differs in different locations.
best wishes!
Stephani Stephenson
steph@revivaltileworks.com
http://www.revivaltileworks.com
Stephani Stephenson on fri 10 nov 06
users, PS
on the last post, I noticed I was kind of sloppy in my own terms
when I refered to 'mixing ' in that post, I was referring to Paulette's
original question about combining a plaster and a gypsum cement, rather
than
'mixing' plaster with water...also I noticed I wrote "Rations" instead
of "ratios"
I wonder if David Hershey is out there, do you combine different types?
gotta step away from the computer....
too much to do today!!!
Stephani Stephenson
steph@revivaltileworks.com
http://www.revivaltileworks.com
John Rodgers on fri 10 nov 06
users
Paulette,
As Stephannie suggested, Donald Friths book "Moldmaking for Ceramics" is
probably the difinitive book on moldmaking out there today. Also, call
U.S. Gypsums Customer Service at Corporate in Chicago. They will be glad
to send you some excellent materials on how to use their products. They
even have stuff about plaster that Donald Frith did not include in his
book. In the past, they were willing to give Plaster Batch calculators
to customers for free. As a newbie, I would not attempt to work plaster
without one. The calculator makes it so much easier.
By the way, for small batches of plaster, where drill powered mixers are
a bit much, I have used a handheld, electric mixing wand. Cost is
generally $12-$20, easy to clean, can be operated with one hand. Just be
sure to rinse off plaster immediately after use while the plaster is
soft and fluid. Easy cleanup then.
USG has some things to say about slaking. Referencing their materials
would be a good thing for that.
As for mixes or blends of plasters, that is going to best be determined
by your doing some tests to find just what works.
Good luck.
Regards,
John Rodgers
Chelsea, AL
Paulette Carr wrote:
> John,
>
> I do use a drill-type mixer - the SuperSafe Vortex mixer, apparently
> designed by Donald Frith, and a larger, turbo mixer for larger
> batches, which I seldom need. The jiffy mixer with two baskets is
> for making larger volumes of plaster than I require, though I might
> be able to stretch it. I would think that the turbo mixer would work.
>
> I am still faced with determining how much time to slake and how much
> time to mix with the blends. A good set of experiments may answer
> the question. An interesting solution often presents more problems
> to solve...
>
> Many thanks!
> Paulette Carr
>
> Paulette Carr Studio
> Member/Potters Council
> St. Louis, MO
>
>
>
>
>
> Date: Thu, 9 Nov 2006 19:25:24 -0600
> From: John Rodgers
> Subject: Re: Plaster molds for use in tile presses - question for
> experts and
> users
>
> Paulette,
>
> I don't know about these particular mixes, but I have done a lot of mold
> making using #1 Pottery Plaster, Ultracal 30, Hydrostone and Hydrocal.
> Never saw a need for dry mixing. I have always used either a high
> quality steel paint mixer, or a stainless steel basket mixer from one of
> the many pottery supply houses. This latter comes in different sizes and
> has a basket made up of two vertical blades, two horizontal blades, and
> two rings to tie them together. The blades have a pitch to them that
> really throws the plaster when mixing. It gives the most thorough mix of
> all.
>
> I would think that given how thorough the basket type mixer will mix,
> there should be no need to dry mix before adding to water, particularly
> since hydrocal and ultracal have longer periods before setting begins.
>
> Regards,
>
> John Rodgers
> Chelsea, Al
>
> ______________________________________________________________________________
>
> 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.
>
>
Paulette Carr on sat 11 nov 06
users
On Nov 10, 2006, at 11:00 PM, Automatic digest processor wrote:
> Date: Fri, 10 Nov 2006 09:16:11 -0800
> From: Susan P
> Subject: Re: Plaster molds for use in tile presses - question for
> experts and
> users
>
> Have read about using a different, but unspecified type of plaster for
> press molds. Is this one way to acheive the same result?
Susan,
I do not know. These are ''specialty" blends (idiosyncratic, as
Stephani said). That is why I was asking questions. Proceed at your
own risk... it is an interesting hypothesis, though. When I have the
time to do the experiments, I will, and then publish. In the
meantime, I invite others to do the same.
Best regards,
Paulette Carr
Paulette Carr Studio
Member/Potters Council
St. Louis, MO
Donald Burroughs on sat 11 nov 06
users
I have tried mixing two types of plaster. A 50/50 ratio of USG no.1 and
USG Hydrocal white. I remember reading about this suggestion in Frank
Giorgini's Tile text. It is a tricky approach at best. You want the
strength of Hydrocal ,but the porosity of no.1 pottery. You have to
calculate the water for each separately. Both have different ratios of
water/plaster as previously indicated. In my attempt, and I have made many
a plaster mold, I felt this to be best left to an advanced user. I also
dry blended my plasters because each has it's own density.
An alternative plaster solution might be another product USG now have
available outside of heavy industry called Ceramcal which I myself am
planning on sampling in the near future. USG in their literature claim it
to be a durable, yet porous enough for ceramic slipcasting.
As for the calculator spoken of, I use it plus USG's online calculator for
water/plaster ratio.It is great for confirming your calculations.
Donald Burroughs
| |
|
