pat gilmartin on tue 12 aug 08
I want to make a plaster mold of a leatherhard plaque. If I seal the surfaces with shellac and use soap as a release before pouring in the plaster, can I then still bisque fire the original and burn off all the shellac and soap?
Nancy Guido on tue 12 aug 08
I have successfully extracted and fired my original once or twice. The trick is to get it out of the mold without ruining it. I don't know how shellac and soap will help, but I don't see how it would hurt.
If you are trying to replicate the leatherhard plaque, remember it has already shrunk just a teeny bit and when you use the new mold with wet clay, it will shrink a little more and it will not be the same size as the original.
nancy g.
Vince Pitelka on tue 12 aug 08
Pat Gilmartin wrote:
"I want to make a plaster mold of a leatherhard plaque. If I seal the
surfaces with shellac and use soap as a release before pouring in the
plaster, can I then still bisque fire the original and burn off all the
shellac and soap?"
Pat -
The shellac will encourage the plaster to stick. Omit the shellac. Just
brush on the mold soap as a release and pour the mold. Make sure that the
original has adequate draft with no undercuts. You should be able to remove
the original from the mold once it has set and then fire the original with
no problems.
- Vince
Vince Pitelka
Appalachian Center for Craft
Tennessee Tech University
vpitelka@dtccom.net; wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka
John Rodgers on tue 12 aug 08
Pat,
I have made many molds, but I have never heard of sealing a still wet
model. Leather hard is still wet, no matter what. It needs to be bone
dry. And keep in mind, that if it is le4ather hard, it has already done
some shrinking from the full size. Any mold you make subsequently, will
be smaller that the original, then any clay piece made in that mold will
be smaller still. Ultimately your piece will be much smaller than the
original model, as well as smaller that the piece you currently have as
a model. Not a good Idea in my opinion. You would be far better off to
make the model from water based clay, then immediately pour the plaster
over the wet clay. When the plaster sets, the clay will give up some of
its water to the plaster, and the clay can then easily be peeled away
from the plaster mold. The mold can then be washed up and dried
thoroughly. An alternative to the water clay would be oil clay. The oil
clay would not shrink and you would get a good full sized mold. - no
shrinkage. You would need to seal the oil clay to prevent oiling the
mold surface. You can do that by spraying or painting the clay surface
with two or three coats of PVA - poly vinyl alcohol. PVA dries hard, but
is water soluble. Just washes off. But it should prevent any oil
migration from the clay to the plaster.
Regards,
John Rodgers
88 GL Driver
pat gilmartin wrote:
> I want to make a plaster mold of a leatherhard plaque. If I seal the surfaces with shellac and use soap as a release before pouring in the plaster, can I then still bisque fire the original and burn off all the shellac and soap?
>
>
>
jonathan byler on tue 12 aug 08
The most difficult part of the process is getting the clay out of the
plaster without damaging it. depending on the shape and the draught
angle of any relief on the clay, it may just pop out as it continues
to dry. the mold release would be superfluous. you could also just
make copies from the mold and fire them. One thing to consider, is
that your leather hard clay is not going to shrink as much as clay
that is pressed into the mold, so the copies will be smaller than the
original.
good luck, and tif this is your first foray into mold making, don't
be too disappointed if you fail the first time out.
-jon
jon byler
3-D Building Coordinator
Art Department
Auburn University, AL 36849
On Aug 12, 2008, at 5:18 PM, pat gilmartin wrote:
> I want to make a plaster mold of a leatherhard plaque. If I seal
> the surfaces with shellac and use soap as a release before pouring
> in the plaster, can I then still bisque fire the original and burn
> off all the shellac and soap?
David Martin Hershey on wed 13 aug 08
Hi Pat and All,
I've made a number of one sided molds like you're contemplating. These
molds are up to 3 inches deep. See: http://www.dmhstudio.com/G_Cats.html
I always make the mold from a leather hard clay master- just wet enough
for it to still stick to the mold board. I never use any release on the
master, but use plastilube mold soap on the mold board and mold form
boards. (diluted 50/50 with water)
I find the easiest way to get the master to release from the mold is to
let it dry in the air for a day or three, and then use compressed air to
help the master release from the mold. Then I flip the mold over, and
the master comes out just like a casting would.
It takes quite a while for the master to dry enough to release, because
of all the water in the plaster. I never fire these masters, but they
usually come out perfectly. Sometimes I continue to work on the master,
and make a variation on the first piece.
I cast the pieces with slip, and then use compressed air to carefully
help release the piece from the mold, before turning it over on a ware
board to remove it from the mold. Same process with press molding. Hold
the casting down with your free hand while using the air, or it might
jump up and get damaged.
If you like the first mold, you can then sacrifice cast it in urethane,
and have a urethane master to make as many molds as you might need.
Depending upon the detail level, plaster molds are usually good for
about 50 castings before they start to degrade badly.
Best, DMH
David Martin Hershey
DMH Studio + Design
2629 Manhattan Ave #137
Hermosa Beach CA USA
90254-2447 310.379.6890
http://www.dmhstudio.com/
Pat Gilmartin wrote:
"I want to make a plaster mold of a leatherhard plaque.
Eleanora Eden on wed 13 aug 08
Pat,
I make plaster molds from soft or leatherhard clay all the time. It is definitely
my preferred method. You only need soap between plaster parts, not between
clay and plaster. You don't need anything, period, between the clay and the
plaster. If you have a nice clean surface on your clay you will have a nice clean
surface on your mold.
The softer your clay original, the easier it is to remove from the finished mold.
With leatherhard clay you will want to use a fork or something to insert into the
clay (in an area you know is thick enough to not pierce your plaster at the same
time) to give you something to help lever the clay piece away from the mold.
Then you just mend that little place. I usually use a little fork in a couple of places
to encourage a stiff clay positive out of the mold.
I prefer soft clay originals because removing them from the mold is so easy.
Eleanora
>Pat Gilmartin wrote:
>"I want to make a plaster mold of a leatherhard plaque. If I seal the
>surfaces with shellac and use soap as a release before pouring in the
>plaster, can I then still bisque fire the original and burn off all the
>shellac and soap?"
--
Bellows Falls Vermont
www.eleanoraeden.com
David Martin Hershey on wed 13 aug 08
Hi James,
I've been using a product from Silpak Inc called RU-440 Urethane RTV
rubber.
http://tinyurl.com/5agftr
Joan Berkwitz told me about it a few years ago, and I've had very good
results since. (Thanks Joani!) It is designed for use with plaster, is
strong but just resilient enough, and so far has a very good library
life. (unlike silicones)
It mixes & pours easily, has a 20 minute working life, and is relatively
safe. (Use in a well ventilated space, and wear disposable gloves.)
Price is a little less than many. They don't seem to have website
ordering, so I just call them. Fast service! 909.625.0056
Best, DMH
David Martin Hershey
DMH Studio + Design
2629 Manhattan Ave #137
Hermosa Beach CA USA
90254-2447 310.379.6890
http://www.dmhstudio.com/
James F wrote:
>What product do you use to make your urethane case molds?
D. L. Engle on thu 14 aug 08
Hi David,
Thanks for the post. (beautiful work BTW) You mentioned a good library life
with the RU-440 Urethane RTV. Could you please tell us about how many
quality years one could expect? Perhaps Joani has some molds older than
yours if you've been using it for only a few. Do you do anything special in
their storage? Many thanks!
Debbie in Valinda So CA
D. L. Engle Sculpture
www.home.earthlink.net/~dlenglesculpture/
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG]On Behalf Of David Martin
Hershey
Sent: Wednesday, August 13, 2008 8:36 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: making a mold w/ leatherhard clay
Hi James,
I've been using a product from Silpak Inc called RU-440 Urethane RTV
rubber.
http://tinyurl.com/5agftr
Joan Berkwitz told me about it a few years ago, and I've had very good
results since. (Thanks Joani!) It is designed for use with plaster, is
strong but just resilient enough, and so far has a very good library
life. (unlike silicones)
It mixes & pours easily, has a 20 minute working life, and is relatively
safe. (Use in a well ventilated space, and wear disposable gloves.)
Price is a little less than many. They don't seem to have website
ordering, so I just call them. Fast service! 909.625.0056
Best, DMH
David Martin Hershey
DMH Studio + Design
2629 Manhattan Ave #137
Hermosa Beach CA USA
90254-2447 310.379.6890
http://www.dmhstudio.com/
James F wrote:
>What product do you use to make your urethane case molds?
Kim Hohlmayer on thu 14 aug 08
Dear Pat,
Yes. :^) --Kim H.
--- On Tue, 8/12/08, pat gilmartin wrote:
> From: pat gilmartin
> Subject: making a mold w/ leatherhard clay
> To: CLAYART@LSV.CERAMICS.ORG
> Date: Tuesday, August 12, 2008, 6:18 PM
> I want to make a plaster mold of a leatherhard plaque. If I
> seal the surfaces with shellac and use soap as a release
> before pouring in the plaster, can I then still bisque fire
> the original and burn off all the shellac and soap?
James F on thu 14 aug 08
>=20
> If you like the first mold=2C you can then sacrifice cast it in urethane=
=2C
> and have a urethane master to make as many molds as you might need.
David...
What product do you use to make your urethane case molds?
Thanks.
...James
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John Rodgers on sat 16 aug 08
David,
Have you ever tried any of the molding products from Polytek, Inc.
(www.polytek.com)? I've used their urethane rubber compounds and other
molding materials for years and been quite happy with them.
John Rodgers
Chelsea, AL
David Martin Hershey wrote:
> Hi James,
>
> I've been using a product from Silpak Inc called RU-440 Urethane RTV
> rubber.
> http://tinyurl.com/5agftr
>
> Joan Berkwitz told me about it a few years ago, and I've had very good
> results since. (Thanks Joani!) It is designed for use with plaster, is
> strong but just resilient enough, and so far has a very good library
> life. (unlike silicones)
>
> It mixes & pours easily, has a 20 minute working life, and is relatively
> safe. (Use in a well ventilated space, and wear disposable gloves.)
>
> Price is a little less than many. They don't seem to have website
> ordering, so I just call them. Fast service! 909.625.0056
>
> Best, DMH
>
> David Martin Hershey
> DMH Studio + Design
> 2629 Manhattan Ave #137
> Hermosa Beach CA USA
> 90254-2447 310.379.6890
> http://www.dmhstudio.com/
>
> James F wrote:
>
> >What product do you use to make your urethane case molds?
>
>
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