Priscilla Wilson and/or Janice Lymburner on fri 11 aug 00
Help! I'm making some plaster molds from clay models, and the clay that =
works best for the models is a dark brown, which colors the plaster =
inside the mold pretty badly. Is there something I can do beyond just =
pressing clay in the mold to try to pick up the brown stuff? Even after =
I do this, I could never hope to cast a white piece even after several =
uses.
Also, a related question: Everything you read about plaster molds says =
something about how important it is to keep them clean. Do you folks do =
anything to keep them clean other than just picking up crumbs with =
clay?? Thanks for your help!=20
Priscilla Wilson in Sautee, GA near the Appalachian Trail
Fredrick Paget on fri 11 aug 00
I usually just hose them down and use a soft brush or sponge at the same
time. Works even with brown clay and if there is a little stain left it
does not come off on white clay.
This works best if the plaster is bone dry to start. My plaster is US
Gypsum Pottery No. 1. If you are using a plain plaster of paris it might be
softer so go easy on the rubbing.
Fred Paget
>Help! I'm making some plaster molds from clay models, and the clay that =
>works best for the models is a dark brown, which colors the plaster =
>inside the mold pretty badly. Is there something I can do beyond just =
>pressing clay in the mold to try to pick up the brown stuff? Even after =
>I do this, I could never hope to cast a white piece even after several =
>uses.
>Priscilla Wilson
>From Fred Paget, Marin County, California, USA
A Reid Harvey on sun 13 aug 00
Priscilla,
Here are several possible remedies, to avoid the insode of your molds
getting brown from using clay as a model. One or more of these should
make it possible to cast a white clay without fear of discoloration. It
is your personal choice which remedy you pursue.
1. Do not use red clay for the model. Try using modeling clay, wood or
another modeling material
2. Perhaps the last quarter inch or so of your model could be a white
clay, applied over the red clay.
3. Cover the bulk of the red clay with plastic wrap, then do the last
quarter inch with modeling clay.
4. Allow the discoloration on the mold to happen. After your first
couple of castings with the white body, subsequent castings should not
show discoloration.
As to the question of keeping the molds clean, I suggest you keep the
closed or covered so that they not get a build up of dust. Keep them
where they will not get wet, since water will damage them. If you have
soaped your molds while making them, be sure to remove the soap with a
light application of white vinegar.
Reid Harvey
Help! I'm making some plaster molds from clay models, and the clay that
=
works best for the models is a dark brown, which colors the plaster =
inside the mold pretty badly. Is there something I can do beyond just =
pressing clay in the mold to try to pick up the brown stuff? Even after
=
I do this, I could never hope to cast a white piece even after several =
uses.
Also, a related question: Everything you read about plaster molds says =
something about how important it is to keep them clean. Do you folks do
=
anything to keep them clean other than just picking up crumbs with =
clay?? Thanks for your help!=20
Priscilla Wilson in Sautee, GA near the Appalachian Trail
Jeff Lawrence on wed 16 aug 00
Hello Slipcasters,
My molds that were used for a red stoneware slip with 8% red iron oxide =
still=20
looked red after a couple of castings with white clay, but the castings =
didn't show any
red to me after the first one. The blush came off the first castings =
with a cleaning sponge,
no problem.=20
I also discovered that molds will absorb noxious construction solvents =
(my neighbor
spilled a bunch under the wall) which I was never able to clean out. =
Though the mold never=20
recovered, it did grow a very impressive beard of sodium silicate fluff, =
over and over again as
I tried to clean the mystery stuff out of it. I always suspected that it =
was a good cathartic=20
regimen for molds, but, scrooge that I am, I denied my other molds the =
treatment (it took=20
too long for the polluted molds to dry out).
Best,
Jeff Lawrence
Sun Dagger Design, etc.
Jonathan Kaplan on thu 17 aug 00
Cleaning plaster molds, as a separate operation from daily cleaning/casting
etc. is kind of more work then really necessary.
If you have a cycle when casting, it should include cleaning as part of
that cycle. We have a very simple one:
1. Soak mold parts and assemble
2. Cast and Dump
3. Demold
4. Clean mold
5. repeat
The cycle repeats itself with the only difference in the last additional step:
6. Store mold
The only materials that should be used to clean plaster molds are water and
a sponge.
If you use a darker color slip before a lighter color slip, you could
easily reverse this sequence.
Alternatively, you could ave 2 sets of molds of the same piece, assuming
you have a block and case so that making production/working molds is
relatiely easy. Then you have a set for dark colored slip and a set for
light colored slip. We use this arrangement for many projects.
Our experience is that if molds are treated with care, they will perform
as they should.
Jonathan
Jonathan Kaplan
Ceramic Design Group LTd/Production Services
PO Box 775112
Steamboat Springs, CO 80477
(970) 879-9139 voice and fax
http://www.sni.net/ceramicdesign
UPS: 1280 13th St. Unit13
Steamboat Springs, CO 80487
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