Originally Posted by
ChrisPer
For the suggestion of Plaster of Paris molds, I wish to suggest not using that.
In the art school, they teach a basic art casting with 'pewter' which has a nice low melting point - scrounged old pewter mugs and vases at up to $10 a pop from antique shops - and the molds are plaster, it has to be baked for four hours or so to remove water of crystallisation so the steam doesn't damage the casting or worse cause an explosion.
I tried plaster before I heard this, and my brass, and tin, castings in plaster molds were terrible.
For lost wax casting the commercial 'plaster' medium is called Cristobalite, it is fine ground silica(quartz?) with a plaster binder. You have to burn it out - ie melt out the wax model, then fire it at 600C for one or more hours to remove everything volatile that may compromise the finish of the casting.
I just tried casting pistons for my puck die, using the 'sharp sand' filled resin method. Perhaps plasterer's sand bound with plaster would make a more heat-stable mold than plaster itself?