I need some advice on casting. We’re used to casting brass, but last
night we were doing a silver casting, and the results are horrible.
None of us have done much with it before. There’s obviously
something basically wrong with what we’re doing, incomplete pieces,
monstrous porosity. There are pieces which look normal, and then
right next to them, shrivelled blackened pieces. The normal looking
pieces are quite brittle, porous and red inside (cuprous or cupric
oxide I suppose). We thought the metal had been heated properly -
completely melted and just a little beyond. We’re using a graphite
crucible with induction heating. Adding a little - a small pinch -
boric acid. The metal, at least compared to brass, is very sticky,
sticks to the stir rod, sticks to the crucible. There’s a slag on
top which doesn’t seem normal from what I’ve read. Using clean pure
silver and copper shot, with a little less than 50% old sprues (cast
by someone else, who was trustworthy). Any clues?
Colin Robertson Jewelry