Foundry Practice

Q: I read that metal can be melted in a homemade charcoal-fired furnace, using an old cast-iron pot for a crucible. Is this a good idea? I want to pour about 20 lbs. of brass.

A: I don’t think this charcoal-fired furnace should be anything but a last resort—gas is a much cleaner, safer, and more controllable fuel. Clinker coal is better than charcoal—it doesn’t produce the ash that flies everywhere, starting fires. But gas—either natural or propane—is best of all. And for God’s sake don’t melt metal in an old cast-iron pot, however modified; get a silicon carbide—or at least a clay-graphite—crucible appropriate for your lifting tongs and pouring ring. These must work as a system if you are to handle molten metal safely. You should be able to get a silicon carbide crucible for about $50, but even if it were $100, it would be worth it—the burns you get from molten metal are no joke.

The number size of the crucible is approximately 1/3 of the pounds of bronze it will hold (you don’t fill them to the brim; leave at least an inch): eg. a #6 will hold about 18 lbs. (It will be less in aluminum, of course). You must be able to slide your lifting tongs all the way down past the crucible to pick it up properly. The crucible, on its melting block, must be below the inside top of the lid by about an inch (remember that everything expands somewhat when heated. It is a good idea to do a dry run when everything is cold, just to make sure everything works smoothly and avoid unpleasant surprises.

I have obtained crucibles from Industrial Foundry and Supply in Oakland, California, 510-633-2133. The Johnson Atelier in Mercerville, New Jersey, 609-890-7777, has a catalog with all the foundry stuff you might need. But crucibles are not that rare an item—check your phonebook under foundry supplies and equipment. Make sure the lifting tongs and pouring rings you buy (or make) fit the crucible you buy. And when you get around to it, use silicon bronze instead of brass; it melts much cleaner and you don’t have to use flux.

by Andrew Werby