good duplicate mold material...

[jerry keller]

I found a plaster mold that I had made years ago, and ran a piece of glass in it this weekend. There is a lot of veiny type of detail to it, and the results were great. I kiln washed the mold first, then ran a piece of 96 1/4" in it at 350-1385- 1.00, then 9999 to 960 -1.0, then 100-900-1.0.

The results were fine. I'd like to run another 10 pieces like this, if the mold would hold up. Any thoughts on whether it will break down soon? And if I were doing this as a solid committment to the design, what type of mold would I make, to re-cast many impressions?

[Bert Weiss]

Look at castalot

[Morganica]

Whoa--"plaster mold" could mean a heckuva lot of things. Do you remember what plaster you bought?

Generally, plain old plaster mixes break down after one or two firings. They can have different kinds of plaster or additives that strengthen the mold enough that for a second firing (or possibly more). And there are cements that are more or less permanent. Without knowing the identify of the mold mix used, it's kinda hard to say. The level of heatwork has an effect as well.

So...what does the mold look like now? Did any of it flake/crumble when you removed the glass? Does it feel softer? Is the detail still sharp?

If your design has no undercuts--and I'm assuming, since the mold you have looks good enough that you're asking about reuse, it doesn't--you could use a permanent casting refractory (Castalot, or one of several others) to remake your mold. Or you can have someone recreate it in ceramic and bisque it. Or you could coat it with something like Luminar Mold Mix Six, which paints on in layers, is fired and becomes a lightweight, permanent ceramic shell.

Just depends on how far you want to go...

[squirrellglider]

If you don't want to go to the expence or bother of doing a bisque fired ceramic mould you could do one in calcium aluminate, sometimes marketed as ciment fondue. It will last many many firings at quite a high temp. Terry.