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[teacherartexchange] Safe to use Slip Clay for Handbuilding


From: Judy Decker (jdecker4art_at_TeacherArtExchange)
Date: Wed Feb 10 2010 - 09:53:54 PST

Greetings Getty Folks,

I know I am late weighing in on this topic, but I was certain that you
could use slip clay for hand building. I asked the Clay Guru, Dr.
Marvin Bartel.

This is his answer (permission granted to share with you):

>> The key thing here is "hand building." Casting slip includes a bit of soda. This allows it to turn to liquid with a lot less water. When casting, less water means less shrinkage as it releases from the mold. It you make slip from clay without the soda, it takes a lot more water to make it liquid. If you pour it in a mold, it shrinks so much that it generally cracks.

I would expect casting slip to be fine for hand building, but I would
avoid contaminating throwing clay with any slip casting clay.

Some artists intentionally cast the clay in traditional vessel form
molds. Then they cut the standard forms into pieces and reassemble
them as cubistic sculpture, figures, animals, etc.

My follow-up question to him was about Soda Ash (a known skin
irritant). This is his response to that question.

>> Yes, soda ash is an irritant in higher concentrations. However, casting slip clay has only one part soda ash for every 1000 or 2000 parts of clay by weight. Most recipes also include a small amount of sodium silicate. The amounts vary, depending on how acidic the clay is. At this concentration, it simply adjusts the PH of clay to make it a bit less acidic, thereby requiring less water to make it liquid. The alkalinity of casting slip is well within the range of many ordinary materials that we safely work with every day. Particularly in winter, any clay work dries out the skin. I use Burt's Bees hand salve.


I really like his suggestion of casting the clay into molds - then
cutting the leather hard clay up and reassembling Cubist style. Let us
know if you try that one.

Any time there is a question about clay, I always go to Marvin's site
and see what he has posted. I didn't see this question covered so, I
emailed him. He has been a long time member of Getty list, but is very
busy now. We are so fortunate he continues to share his knowledge
through his web site(s).
(follow the links to his Art Education resources)


Judy Decker

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