ArtMetal

Hello Sahid Actually Plaster of Paris is same as #1 Molding Plaster and is fine for Investment casting. I use a standard mix of about 50% sand to 50% plaster and vary the proportions only for exceptions. The sand used is a general blend called Brick Sand here and is commonly used to mix with Portland Cement for concrete and mortar. Nothing fancy at all. The varying sizes of the grain in it are a plus with the coarsest grains being slightly smaller than grape seeds. The mix used next to the body of the wax or surface to be cast are often smaller and would fit through a window screen.

To be more precise, put the words Investment Casting in the artmetal search engine and you will get quite a bit of information on this already written. In addition here are a few other related comments:
On investment casting
http://www.artmetal.com/brambush/forum/bramyak1/messages/125.html

On Casting waxes
http://www.artmetal.com/village/chat/main/transcrp/980423MN.htm

On comparing Plaster / Sand Investments vs. Ceramic Shell
http://www.artmetal.com/brambush/forum/bramyak1/messages/177.html

On Ancient Casting Methods
http://www.artmetal.com/brambush/forum/bramyak1/messages/125.html
www.artmetal.com/bpfink Bruce P Fink

bpfink