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I have some 1/4 in. Amaco fiber shelf liner that I would like to make a mold with. I'd like to stack 2 layers, making a 1/2 in. deep slump mold. Any reason this won't work? Do I need to burn out this material first? Do I need to coat the top with kiln wash? Should I vent the kiln slightly when slump firing? I hope I can get more than 1 firing with the mold, but it's not be possible. Thanks for any suggestions.

Chances are you don't need to prefire the mold. Venting is probably a good idea. It will stink. If it were me, I would choose to use ½" fiber blanket, which has no binders to burn out and can be reused over and over. Fiber paper has a lot less structure to it, and may only work for a single firing, unless you delicately remove and replace the glass.

Do you have to use a rigidizer with a 1/2 in. blanket?

Patgsc wrote:Do you have to use a rigidizer with a 1/2 in. blanket?

I never use rigidizer. There are 2 kinds of rigidizer, colloidal silica, and colloidal alumina. Silica is the more common one, and it sticks to glass, so it needs kiln wash over it. I don't use it because it would serve me no purpose. I often use piles of fiber blanket for molds. I pile it up, place glass on top, and fire away. When I am done, I put the fiber back in a bag, and use it again for something else. Nothing could be simpler. Fiber blanket has no binders in it, so you just use it. I fire directly on my kiln floor, which is covered with fiber blanket. Sometimes I use various powders on top of it, to fill in the holes or cover the whole blanket. Sometimes not. I find that people often make this all way more complicated than need be.

Sounds like a fun and simple way to go! Thanks.