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I have a customer that collects antique lamps. He is bringing me an broken slumped piece so I can slump new shades for him...I am using Moist pack but it is too bumpy..do I just need to sand it or is there another product that is better to use when trying to make a mold from an existing shade...thanks so much for the help! Betsy

We use a castable refractory. It's normally used for boiler repairs. Mixes up like cement. Drys hard and smooth, requires no kiln was, but weighs a ton. It doesn't shrink, which is most important. I would really love to find another material, however. Something lighter, easier to work with, but doesn't shrink . I've posted this query before with no results. I'm hoping someone may have found something by now. - Barbara

Moist Pack is the same as fiberblanket & colloidal silica, right? Then you can sand it after it has air dried and before you fire it.

What about plaster silica. I don't know much about this though, I imagine it wouldn't last very long. But if you put fiberglass in it or wire that might help.

Amy

The problem with plaster is that it shrinks. Replacing a bent panel lamp piece means only needing that mold for probably 1-2 firings. We don't need a permanent mold, but that's what the refractory is. And, my moist pack is bumpy too. It's just a lot of trouble. A lightweight casting material, good for 1-2 firings that didn't shrink, would be perfect. You'd think something so *simple* would be available. - Barbara

Fine sand with molasses or bentonite ( a fine particle clay) to hold it together. A liitle higher tech would be sand with sodium silicate mixed in and carbon dioxide gassed into it to harden it. There may be something on this in Henry Halems Glass Notes website. It's in his book for sure.

Look up foundry or home foundry casting techniques in your favorite search engine. Put "Dave Gingery" into the search and it should take you to some good ones.

or...

Lindsay books has lots of this info, particularly the ones on basic metal casting by Dave Gingery. I forget the URL but they are on the web. Lots of other wild and crazy tech books too. They're a hoot.

thanks for the ideas....I've just tried sanding the dried moist pack mold. It had some "soft" spots and thus created some "divets". I'll check out the other suggestions.....thank you all so much! Betsy