Snail Scott on tue 28 dec 04
At 10:45 AM 12/28/2004 -0600, you wrote:
>Plaster shrinks away from the damp clay forms just fine, but I'm thinking I
>should coat the dry one with Murphy's before using it, just as though it
>were a plate or bowl, is that probably safe to assume?
Yep. The dry clay probably won't survive the strain
of the plaster setting around it, but it'll separate
just fine with a really good (multiple) coating of
soap, and leave a workable mold.
-Snail
Kate Johnson on tue 28 dec 04
Hi again, all, and thank you for the many helpful answers to my
plaster-disaster, on and offlist!
I'm gearing up to try again, and have another question--the ones I made
successfully last time were forms I'd made out of damp clay. One of the
pieces I plan to try this time is a dry-but-raw form I made some time back
but didn't get the mold made.
Plaster shrinks away from the damp clay forms just fine, but I'm thinking I
should coat the dry one with Murphy's before using it, just as though it
were a plate or bowl, is that probably safe to assume?
Many thanks...amazing how many questions occur when you're trying to avoid a
new disaster.
Regards,
Kate Johnson
Graphics/Fine Arts
http://www.cathyjohnson.info/
http://www.epsi.net/graphic/
http://www.ebsqart.com/Artists/cmd_1494_profile.htm
Carol Ross on tue 28 dec 04
Hi Kate -
I'd coat it - the water which made it release easily from plaster is
now gone. The dry clay form will absorb water and make it difficult to
separate... That's my best guess, anyway. Good luck!
Carol R.
On Dec 28, 2004, at 10:45 AM, Kate Johnson wrote:
> Hi again, all, and thank you for the many helpful answers to my
> plaster-disaster, on and offlist!
>
> I'm gearing up to try again, and have another question--the ones I made
> successfully last time were forms I'd made out of damp clay. One of
> the
> pieces I plan to try this time is a dry-but-raw form I made some time
> back
> but didn't get the mold made.
>
> Plaster shrinks away from the damp clay forms just fine, but I'm
> thinking I
> should coat the dry one with Murphy's before using it, just as though
> it
> were a plate or bowl, is that probably safe to assume?
>
> Many thanks...amazing how many questions occur when you're trying to
> avoid a
> new disaster.
>
> Regards,
> Kate Johnson
> Graphics/Fine Arts
> http://www.cathyjohnson.info/
> http://www.epsi.net/graphic/
> http://www.ebsqart.com/Artists/cmd_1494_profile.htm
>
> _______________________________________________________________________
> _______
> Send postings to clayart@lsv.ceramics.org
>
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>
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> melpots@pclink.com.
>
John Rodgers on tue 28 dec 04
Kate, if your dry form has any porosity at all you may have trouble with
the plaster sticking. Clay bisque is a bad choice unless you seal it.
If your model is not wet clay, then the surface needs to be sealed
before you apply a mold release agent, be it soap or any other mold
release. Several coats of shellac work well on some surfaces. I have
also used spray can polyurethane. After drying a good coat of soap did
the job.
If you plaster mold does not need to keep it's absorption qualities, you
could use vaseline as the mold release applied directly to the model
surface. This will seal the pores of the model, but will adhere to the
surface of the new plaster casting. Not a problem if water absrption is
not an issue in the new plaster casting.
Regards,
John Rodgers
Chelsea, AL
Kate Johnson wrote:
> Hi again, all, and thank you for the many helpful answers to my
> plaster-disaster, on and offlist!
>
> I'm gearing up to try again, and have another question--the ones I made
> successfully last time were forms I'd made out of damp clay. One of the
> pieces I plan to try this time is a dry-but-raw form I made some time
> back
> but didn't get the mold made.
>
> Plaster shrinks away from the damp clay forms just fine, but I'm
> thinking I
> should coat the dry one with Murphy's before using it, just as though it
> were a plate or bowl, is that probably safe to assume?
>
> Many thanks...amazing how many questions occur when you're trying to
> avoid a
> new disaster.
>
> Regards,
> Kate Johnson
> Graphics/Fine Arts
> http://www.cathyjohnson.info/
> http://www.epsi.net/graphic/
> http://www.ebsqart.com/Artists/cmd_1494_profile.htm
>
> ______________________________________________________________________________
>
> 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.
>
>
Kate Johnson on tue 28 dec 04
> Kate, if your dry form has any porosity at all you may have trouble with
> the plaster sticking. Clay bisque is a bad choice unless you seal it.
>
> If your model is not wet clay, then the surface needs to be sealed
> before you apply a mold release agent, be it soap or any other mold
> release. Several coats of shellac work well on some surfaces.
What I'm dealing with is a dried clay/greenware form--it's not bisqued, but
it's not damp any more either. What it IS is a really good shape, and I
hate to toss it..
I have
> also used spray can polyurethane. After drying a good coat of soap did
> the job.
Will give that a try, thank you.
>
> If you plaster mold does not need to keep it's absorption qualities, you
> could use vaseline as the mold release applied directly to the model
> surface. This will seal the pores of the model, but will adhere to the
> surface of the new plaster casting. Not a problem if water absrption is
> not an issue in the new plaster casting.
Definitely wanting the absorptive qualities of the plaster to aid in even
drying and release, so I guess Vaseline is Right Out.
Some of the items I was trying to make molds from yesterday (Plaster
Disaster Day) are not absorptive at all (answering Carol here too...)--I was
using existing bowls/plates, some porcelain, some enamel/graniteware.
Hoping the Murphy's will act as enough of a release when I get the plaster
proportions right, though!
Some original English and Colonial slump molds were made from bisqued clay,
some of them with designs inscriped in the surface--I plan to try that,
too.
So many experiments, so little time!
Thanks, all...
Best--
Kate
Debbie on tue 28 dec 04
Hi Kate,
If you pour plaster over a dry clay form, the dry clay will suck water out
of the plaster and cause it to set poorly. That would change the water/
powder ratio in the wet plaster up against the clay to a dryer & no longer
homogenous mix).
You need to seal the dry clay so that no water from the wet plaster can seep
into it. If that were to happen, in addition to making your plaster mix week
or fail, it could dissolve the surface of your clay form! Wax resist is a
good choice to seal the clay.
Also be sure that the clay form you are molding has no undercuts and is
firmly attached to it's base (so it won't float up into the wet plaster).
Plaster will not shrink but since dry clay won't either you may still have a
bit of a challenge getting the set plaster off the clay. Plan for this
either by fixing the clay very firmly to it's base board (and popping the
plaster mold away from both clay and the base board) or plan on destroying
the clay by carefully digging it out of the plaster. Good luck!
Best Wishes, Debbie
> -----Original Message-----
> From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG]On Behalf Of Kate Johnson
> Sent: Tuesday, December 28, 2004 8:46 AM
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: another mold-making question
>
>
> Hi again, all, and thank you for the many helpful answers to my
> plaster-disaster, on and offlist!
>
> I'm gearing up to try again, and have another question--the ones I made
> successfully last time were forms I'd made out of damp clay. One of the
> pieces I plan to try this time is a dry-but-raw form I made some time back
> but didn't get the mold made.
>
> Plaster shrinks away from the damp clay forms just fine, but I'm
> thinking I
> should coat the dry one with Murphy's before using it, just as though it
> were a plate or bowl, is that probably safe to assume?
>
> Many thanks...amazing how many questions occur when you're trying
> to avoid a
> new disaster.
>
> Regards,
> Kate Johnson
> Graphics/Fine Arts
>
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