Z Jacobson on sat 26 jul 08
Hi everyone=2C=20
=20
I've been reading the posts for a while now but this is my first time posti=
ng. I wanted to ask a question continuing the discussion on slip casting in=
to mold making
=20
I am pretty much a newbie at this slip casting/mold making thing but I real=
ly love it. I'm having some problems in making molds. I'm making 2 part mol=
ds and the first part is coming out fine. After I pour the 2nd section and =
pull the mold apart=2C I'm getting a weird texture where the two halves com=
e together and a very thin uneven layer of plaster is not sticking to the n=
ewly poured section of the mold. This plaster will wash off the first 1/2 b=
ut leaves an indented slightly modeled texture on the second 1/2. Does anyo=
ne know what this is caused by and what I can do?
=20
To see what kind of work I do=2C check out my website=2C www.zjacobsonart.c=
om
=20
=20
Thanxs
Z Jacobson =20
Z Jacobson
Wildly Energetic Ceramics
www.zjacobsonart.com=20
z@zjacobsonart.com
Santa Fe=2C NM=
Bill Merrill on sat 26 jul 08
Your plaster mix could be poured at the wrong time or your water/plaster
ratio is weal in the plaster department. A good water plaster mix
is 2 1/2 pounds of plaster (up to 3 lbs of plaster) per quart of water.
To measure how much plaster you need is figured or Guestamated by
multiplying the height X width X thickness. So if you have something
that is 1" X 8" X 10" you come up with 80 cubic inches. For every 80
cubic inches you need 1 quart of water and 2 1/2 pounds of plaster. Use
room temp water. Measure the water and then gently sift the plaster
into the water. Do not stir the mix. Let it sit nd absorb. After
sitting, gently stir and you will get a smooth creamy mix. I don't pour
the mix until I can drag my finger across the top and there remains a
frosting like trail. At this point I pour the piece. Stir the mix
before you pour to mix in any water that has risen to the surface. Also
tap your mixing bucket to alleviate air bubbles. If you have detail to
mold, do a splash coat on the detail before you pour or put the
thickened plaster on by hand. Cold water slows the setting time of
plaster. Do not separate the mold until the heat has dissipated.
Plaster is weak when it is going through the exothermic heating process.
If you need to color your plaster for some reason, use old fashioned
bluing that is used in laundry. I have used it for a splash coat in
sculpture and the put white plaster over it.=20
Wally Higgins taught commercial/art plaster classes at Alfred many years
ago. It was a most interesting class. =20
Hope this made sense !!!!!!
=20
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Z Jacobson
Sent: Saturday, July 26, 2008 5:14 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: More slip casting and mold making
Hi everyone,=20
=20
I've been reading the posts for a while now but this is my first time
posting. I wanted to ask a question continuing the discussion on slip
casting into mold making
=20
I am pretty much a newbie at this slip casting/mold making thing but I
really love it. I'm having some problems in making molds. I'm making 2
part molds and the first part is coming out fine. After I pour the 2nd
section and pull the mold apart, I'm getting a weird texture where the
two halves come together and a very thin uneven layer of plaster is not
sticking to the newly poured section of the mold. This plaster will wash
off the first 1/2 but leaves an indented slightly modeled texture on the
second 1/2. Does anyone know what this is caused by and what I can do?
=20
To see what kind of work I do, check out my website,
www.zjacobsonart.com
=20
=20
Thanxs
Z Jacobson =20
Z Jacobson
Wildly Energetic Ceramics
www.zjacobsonart.com=20
z@zjacobsonart.com
Santa Fe, NM
Jeff Longtin on sat 26 jul 08
Wow!
I step away from Clayart for a few years and the first question I pull up is
a slip-casting/mold-making question? (The universe is telling me something.)
Hello Z. (and your name is?)
I had just that same problem today. I cast a plaster form, from a plaster
mold, and had the "fuzz" show up. A little bummed at first but I realized I
need to be patient.
A few sources for your problem:
Are you measuring your plaster mix so that the proper ratio is used
consistently?
Are you allowing the plaster enough time to setup properly?
and lastly:
Are you allowing the seperating compound time to dry?
In my case I realized that I didn't take the hot summer weather into
account. I applied three coats of Murphy's Oil Soap but I needed to use four or
five. The coats were drying REALLY quickly but I was certain it would be no
problem. I was wrong.
I simply cleaned the plaster forms and decided a day of rest would be good.
(for me and the molds)
You're represented by del Mano? Small world! I was in a show there back in
the 80's.
do...do...do...do
Jeff Longtin
feelin' cosmic in minneapolis
In a message dated 7/26/2008 12:46:31 P.M. Central Daylight Time,
purplezippy@HOTMAIL.COM writes:
Hi everyone,
I've been reading the posts for a while now but this is my first time
posting. I wanted to ask a question continuing the discussion on slip casting into
mold making
I am pretty much a newbie at this slip casting/mold making thing but I
really love it. I'm having some problems in making molds. I'm making 2 part molds
and the first part is coming out fine. After I pour the 2nd section and pull
the mold apart, I'm getting a weird texture where the two halves come
together and a very thin uneven layer of plaster is not sticking to the newly poured
section of the mold. This plaster will wash off the first 1/2 but leaves an
indented slightly modeled texture on the second 1/2. Does anyone know what
this is caused by and what I can do?
To see what kind of work I do, check out my website, www.zjacobsonart.com
Thanxs
Z Jacobson
Z Jacobson
Wildly Energetic Ceramics
www.zjacobsonart.com
z@zjacobsonart.com
Santa Fe, NM=
**************Get fantasy football with free live scoring. Sign up for
FanHouse Fantasy Football today.
(http://www.fanhouse.com/fantasyaffair?ncid=aolspr00050000000020)
John Rodgers on sun 27 jul 08
Z,
A few things ....
Old plaster will either set before you get it mixed, or it won't set or
it will take near forever to set.
When you buy plaster, be sure you check with yur supplier that the
plaster is not more than 90 days old.
To prevent bubbles, after mixing but before pouring - spritz the top the
plaster in the bucket with alcohol. Instant bubble removal.
After spritzing the plaster in the bucket, spritz the surfaces to be
molded. Then pour the plaster in the deepest part of the mold and do it
in a single continuous pour. All the bubbles will be broken and there
will be no pits in the surface of the new mold.
Good luck.
John Rodgers
Chelsea, AL
Z Jacobson wrote:
> Hey Bill and Jeff,
> both of you are suggesting similar causes. I am measuring and mixing correctly but I'm definitely not waiting to pour as long as Bill is suggesting. I get nervous it will set up too quickly before I'm done pouring. I also could be separating the mold too quickly, its still warm when I do this. I will try to be more patient when making my next mold. Also, is there a way to know how much mold soap to use? Could you explain what you mean by a splash coating?
> thanxs
> Z Jacobson (yes, Z is my name)
> Santa Fe, NM
> www.zjacobsonart.com
>
>
Z Jacobson on sun 27 jul 08
Hey Bill and Jeff=2C
both of you are suggesting similar causes. I am measuring and mixing correc=
tly but I'm definitely not waiting to pour as long as Bill is suggesting. I=
get nervous it will set up too quickly before I'm done pouring. I also cou=
ld be separating the mold too quickly=2C its still warm when I do this. I w=
ill try to be more patient when making my next mold. Also=2C is there a way=
to know how much mold soap to use? Could you explain what you mean by a sp=
lash coating?
thanxs
Z Jacobson (yes=2C Z is my name)
Santa Fe=2C NM
www.zjacobsonart.com=
Bill Merrill on sun 27 jul 08
Splash coating is generally done on forms that have texture or
undercuts. If you put your hand into the plaster and then shake the
plaster onto the piece so as to get into finely detailed places and
undercuts. This is usually done on sculpture. Some of the splash coat
can run, but when the splash coat sets up some a heavier coat can be
applied. Usually, a piece you pour may not have a splash coat on it.
Tap the mold to get bubbles off the piece you are casting. As far as
waiting to pour the plaster, if you pour when the plaster is thin, it
has a much better chance to find its way through the mold joint. If you
place your hand in the plaster bucket and agitate the plaster and then
pour with a heavier plaster you will also alleviate the problem you are
having with the plaster being frothy and weak on the surface of the
plaster. =20
=20
An extremely good book on plaster is:
=20
Mold Making for Ceramics by Donald Firth. =20
=20
The book will be expensive, but is worth every penny!! It has a plaster
calculator in it, kinda like on of the old slide rules. It also
discusses various plasters and the water content need for different
plasters.
=20
I mentioned in the lst memo To wait for the mold to cool before taking
apart. The plaster is still weak at that point. Patience!!
=20
You will learn a lot more about the workings of plaster if you do a
small measured batch and watch the plaster. Drag your finger across the
plaster in the bucket. As it sets up, the peaks go higher without
settling down. Pour when it is thicker than cream and a little thinner
tan frosting. These experiments will make it so when you are casting a
large amount of plaster, you'll know what to expect and when to pour.
When the plaster is just past the frosting stage that is when you can
remove excess plaster from the bottom of the mold ny dragging a straight
edge across to remove the excess.
=20
Bill
=20
Cast a wedging surface. Build a form using melamine. Screw it
together. Brush on mo;d soap. Figure how much plaster and water you
need. I have 30" X 30" x 4" wedging blocks. If one gets damp, I use
the other on. When you pour into a smooth surface,like Melamine, the
wedging surface will be like glass. =20
=20
=20
=20
=20
=20
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Z Jacobson
Sent: Sunday, July 27, 2008 8:38 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: More Slip Casting and Mold Making
=20
Hey Bill and Jeff,
both of you are suggesting similar causes. I am measuring and mixing
correctly but I'm definitely not waiting to pour as long as Bill is
suggesting. I get nervous it will set up too quickly before I'm done
pouring. I also could be separating the mold too quickly, its still warm
when I do this. I will try to be more patient when making my next mold.
Also, is there a way to know how much mold soap to use? Could you
explain what you mean by a splash coating?
thanxs
Z Jacobson (yes, Z is my name)
Santa Fe, NM
www.zjacobsonart.com
Jeff Longtin on sun 27 jul 08
Hey Z!
I let the plaster/water sit for 2 minutes. I mix for two minutes. I let the
mix sit for a minute. (I basically set a timer for 5 minutes and watch my
intervals.)
Using a timer helps me know if I have dry plaster, i.e. new, or if I have
wet plaster, i.e. old plaster.
After 5 minutes new plaster is still fairly fluid so I pick up the bucket
and swirl it a bit. When it gets to the "melted ice cream" consistency I pour
it. If I pour it while it is still runny it usually runs out the pour box.
Like Bill mentioned, I stick a spatula, or my fingers, into the pour and
gently vibrate to move any bubbles still in the mix.
I then let the plaster sit 20 minutes. (Correction: I set the timer for 25
minutes and watch my intervals from there.)
If you're using old plaster, and using warm water, the plaster might be
completely hard after 25. If you use cold water, and the plaster is new, it might
need 5 or 10 minutes more.
and sometimes I've done all of the above and I still get plaster residue and
have to redo the pour. Like clay, sometimes it just doesn't work the way you
want it to, sometimes there are happy accidents, sometimes there are really
annoying accidents.
Snail Scott and Jonathan Kaplan have posted many very explicit instructions,
on making molds, over the years. Ya might check out their postings as well.
Take care
In a message dated 7/27/2008 2:47:19 P.M. Central Daylight Time,
purplezippy@HOTMAIL.COM writes:
Hey Bill and Jeff,
both of you are suggesting similar causes. I am measuring and mixing
correctly but I'm definitely not waiting to pour as long as Bill is suggesting. I
get nervous it will set up too quickly before I'm done pouring. I also could be
separating the mold too quickly, its still warm when I do this. I will try
to be more patient when making my next mold. Also, is there a way to know how
much mold soap to use? Could you explain what you mean by a splash coating?
thanxs
Z Jacobson (yes, Z is my name)
Santa Fe, NM
www.zjacobsonart.com=
**************Get fantasy football with free live scoring. Sign up for
FanHouse Fantasy Football today.
(http://www.fanhouse.com/fantasyaffair?ncid=aolspr00050000000020)
Z Jacobson on mon 28 jul 08
Some of you guys seem to be unbelievably brilliant at the technical stuff. =
Me=2C not so much. I'm having 2 issues with my slip casting recipe. The cas=
tings come out really well and fit my clay body quite nicely. The recipe is=
cone 1 -4=2C I prefer to fire to 01 but have been firing to 1 because of t=
he recipe still I'd rather be in the middle of the range than at the bottom=
=2C is there a way to lower the firing temperate?=20
=20
The other issue is that the castings shrink a lot!! while there isn't a pro=
blem where they come in contact with my clay body=2C they are very small...=
.the first time I made the recipe=2C for the Kaolin I used approximately 50=
/50 Helmar and Kaopact because thats what I had=2C the next time I used EPK=
to see if it would also work=2C which it did. I know the EPK shrunk quite =
a bit. Is there a way to reduce the shrinkage?
=20
Heres my recipe
=20
Kaolin 30
Neph Sy 26
Kentucky Ball #4 20
Silica 11
Talc 13
=20
H2o 5 Gal
Sodium Silicate 4.8 oz
=20
Thanxs!!
Z Jacobson
=20
=20
Z Jacobson
Wildly Energetic Ceramics
www.zjacobsonart.com=20
Santa Fe=2C NM 87501
=
Michael Wendt on mon 28 jul 08
Z,
If I read you correctly, your batch is 100 LBS
of dry mix and 40 LBS of water.
That's a bit more water than we use.
If you reduce the water a little each batch,
eventually you will find the shrinkage
will be less. When we cast, our batch is:
17.5 LBS Helmer Kaolin
4.4 LBS Custer Feldspar
4.4 LBS A-270 Nepheline Syenite
8.8 LBS 200 mesh Silica
to this we weigh in 15 LBS of water
with 2 ounces of Darvan already added.
I always add all the clay first and mix it a
while, then add the other ingredients, mix
and adjust drain time using a home made tube
viscometer consisting of an 18" x 2" I D plastic
pipe with a cap on one end which has a 1/4"
hole drilled in it. Drain time for best results is
45 seconds until the steady stream breaks into
drops.
After the slip ages a few days, you may need to
add a few drops of Darvan at a time until to get
the same drain time.
Stated as a general rule, we want the least amount
of water in casting slip that will still allow good
casting properties.
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave.
Lewiston, Id 83501
U.S.A.
208-746-3724
wendtpot@lewiston.com
http://www.wendtpottery.com
http://UniquePorcelainDesigns.com
Z wrote:
Some of you guys seem to be unbelievably brilliant at
the technical stuff. Me, not so much. I'm having 2
issues with my slip casting recipe. The castings come
out really well and fit my clay body quite nicely. The
recipe is cone 1 -4, I prefer to fire to 01 but have
been firing to 1 because of the recipe still I'd rather
be in the middle of the range than at the bottom, is
there a way to lower the firing temperate?
The other issue is that the castings shrink a lot!!
while there isn't a problem where they come in contact
with my clay body, they are very small....the first
time I made the recipe, for the Kaolin I used
approximately 50/50 Helmar and Kaopact because thats
what I had, the next time I used EPK to see if it would
also work, which it did. I know the EPK shrunk quite a
bit. Is there a way to reduce the shrinkage?
Heres my recipe
Kaolin 30
Neph Sy 26
Kentucky Ball #4 20
Silica 11
Talc 13
H2o 5 Gal
Sodium Silicate 4.8 oz
Thanxs!!
Z Jacobson
Z Jacobson on tue 29 jul 08
Michael=2C thanxs for that=2C if the water is the answer=2C awesome=2C for =
once an ez solution. I'll try it on my next batch.
BTW=2C why do you use Helmar Kaolin as opposed to other kinds?
=20
thanxsZ Jacobson
Wildly Energetic Ceramics
www.zjacobsonart.com=20
Santa Fe=2C NM
=
Steve Slatin on tue 29 jul 08
Michael --
Maybe something is missing from the
recipe you gave? I get his ratio as
100/40 = 2.5 dry to wet, and yours
as 35.1/15 = 2.34 dry to wet (2.32
if I add in 2 oz weight for the darvan).
Best wishes -- Steve Slatin
--- On Mon, 7/28/08, Michael Wendt wrote:
> Z,
> If I read you correctly, your batch is 100 LBS
> of dry mix and 40 LBS of water.
> That's a bit more water than we use.
> If you reduce the water a little each batch,
> eventually you will find the shrinkage
> will be less. When we cast, our batch is:
> 17.5 LBS Helmer Kaolin
> 4.4 LBS Custer Feldspar
> 4.4 LBS A-270 Nepheline Syenite
> 8.8 LBS 200 mesh Silica
> to this we weigh in 15 LBS of water
> with 2 ounces of Darvan already added.
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