slumping casting question

No it will not work. The mold as you know is a fired ceramic and your glass will stick at the casting temperature ruining the mold as well as the cast piece.

stephen cartwright

The mold can take the heat. No problem there. If completely prepared with shelf primer glass will not stick. Problem is properly filling with glass to get level full surface. Mound glass in center so it flows up sides to avoid sharp stickers. Small pieces and maybe more time to get out bubbles. You might also be fighting bubbles between designed piece and molded piece. How about creating an almost full mold first, build design on top surface, cover with broken up glass (clear frit) to fill completely? Also you might want to fire polish the final piece to soften the surface texture of the dome made in the mold. (I am picturing the finished product as a paper weight shaped dome.) Good luck and remember long anneal times. Include mold thickness as part of calculation.

Clay type molds can take the heat but you want to go slow and not shock them going up or down to fast, do not crash cool. What is a "ball" mold? I can't visualize what you are trying to do.

Let me append my response a bit. Thick shelf primer will tend to stick to the cast glass. Another solution is to take some thin fiber paper and carefully wet it so that you can mold it into the slumping mold. Thin fire may be too thin. I would recommend 1/16 inch fiber paper. That should give you a good release. The fiber paper will tend to adhere to the casting but will usually wash off.

It's called a ball surface mold. I tried to find an online link but can't seem to get into their catalog. Picture this ) on its side. The surface of the slumped piece will have no flats on it, shaped as if you cut a round section out of a ball such as a 10" rubber ball. Here is a face on view made in the mold he is describing:

is another from a 22.5" ball surface mold: wish I had a full side view for you. The project he is planning sounds like a great idea.

This will probably work, but I would be concerned about degrading the mold. They're not designed to take casting temps, and it will probably shorten its life span even if it doesn't crumble immediately.

Better idea might be to make a plaster casting of the mold, then a cast of the cast.

-Kalera

Henry Halem wrote:

Seems to be a bowl mold with no flat bottom - to make a non-functional art bowl? I was thinking maybe it was a paper weight type mold.

Clay that is properly fired to bisque is usually fired to 2300 degrees (depending on the type of clay). Too bad my kiln will not go that high or I would make my own stands and lamp bases. I made a shallow mold, more like an imprint out of thick clay. It worked OK but I noticed the glass had raised it self up away from the clay when it cooled ( no sticking problems there) probably caused by the depressions in the clay. Did have trouble with one big bubble but that was my fault, that's what experiments are for - to help me think ahead for possible problems and solutions. Now if only my memory cells will stick around, wish I could by a memory upgrade.

My suggestion to Stephen would be to try a smaller version ( a small bowl) as a test. That way he will get an idea of the temperature his kiln will need to melt all that glass down. My small kilns definitely need more time/temp then 1465 to fully fuse glass than my big kiln.

[It's only stoneware and porcelain that are fired that high, and it's done in the glaze fire, generally not the bisque (it's best to leave the ware porous, so the glaze adheres better). Many ceramic items are fired much lower, around cone 06, or 1813 degrees F. Since there's no need for stands and lampbases to be extremely hard, you shouldn't think it's impossible to fire them in your kiln, which probably can attain these temperatures. Here's a temperature chart with cone equivalents: Werby

I made a shallow mold, more like an

>> > Here is another from a 22.5" ball surface mold:> >

>> > I wish I had a full side view for you.> >