>What can be added to plaster to keep it from cracking when tryin go make a
>mold. I have not ventured into this area but a friend of mine is and
>trying to cast metal using the plaster molds. He is drying the plaster in
>oven to get rid of water, but some cracks occur and when pouring the
>metal, cracks show up.
I'm just catching up after a hectic end of the year, so this may be to late to
help you. The plaster I used for metal casting was a special blend to start
with. It was called "investment" and you can buy it through catalogs- Rio
Grande comes to mind. Also, depending on what kind of metal, the mold may need
to be really hot when you cast to prevent problems. You want it to be at the
casting temperature of the metal- so his oven might need to be more like a
kiln. A great book on this is Practical Casting by Tim McCreight.