Drape over clay mold - workable?

[Bonnie Rubinstein]

I know we are not supposed to drape over a clay mold. However, I am making a complicated shape for a sconce and slumping into it might not work. So, if I making a clay mold, with gentle sides and open at one end (so it doesn't drape there), would I be able to drape over without breaking the mold?

Thank you,
Bonnie

[Bert Weiss]

It is all about shape and configuration. If the glass has somewhere to go as it shrinks more than the clay, it will be fine. If the clay gets trapped, it will crack. I solved one drape over challenge by making an investment mold instead of a clay one.

[Brock]

IMO, the best way to ensure success slumping over clay, and I have done it often, is to create a "draft". One way is to wrap the entire mold, where it contacts the shelf, in a 1/2" band of FP. This allows the glass to compress the FP and even to ride up it in some cases. It really can be done . . .

[Bonnie Rubinstein]

Hi Bert,

not sure how an investment is done..but I believe it is much more complex. also, is it re-usable?

I don't think it will be trapped, as one end will not be draped over the clay, but more on top. I guess I can go through the process of making the clay mold and trying.

Brock..the FP sounds like good insurance. Thx.

[Bert Weiss]

Hi Bert,

not sure how an investment is done..but I believe it is much more complex. also, is it re-usable?

I don't think it will be trapped, as one end will not be draped over the clay, but more on top. I guess I can go through the process of making the clay mold and trying.

Brock..the FP sounds like good insurance. Thx.

I was working with a friend who is a potter. She made a bisqued face. I tried draping a large piece of 6mm float over it with the idea of the glass forming over the face and flattening out on the shelf. After a couple of cracked pieces, I decided to make a thin rubber mold with a plaster mother, of the clay face. Then I cast a homemade refractory mold. I forget if I got more than one firing from the mold, but the rubber mold makes it simple to reproduce. The refractory face worked perfectly to solve the problem. The glass formed over the face and flattened out on the shelf, remaining intact. There are durable refractory cements, but I have no clue how they expand and contract relative to the glass. My mix was plaster/silica and other stuff.

How you solve the problem will dictate the look you get. There are obviously different approaches that will work.

[Bonnie Rubinstein]

okay..I see..so the rubber does make it easy to reproduce again.

I will process these options during the night.. I seem to have 'glass relevations' by the morning.

Tomorrow I was going to buy the clay in St. Paul.. maybe not.

[Bonnie Rubinstein]

Brock, was that 1/2" thick paper, vs. 1/2" high?

[Brock]

Brock, was that 1/2" thick paper, vs. 1/2" high?

1/8" thick paper, cut in a 1/2" band around the perimeter of the mold where it sits on the shelf.