The best crucibles are made from a pure fire clay, mixed with finely ground cement of old crucibles, and a portion of black lead or graphite: some pounded coke may be mixed with the plumbago. The clay should be prepared in a similar way as for making pottery ware: the vessels, after being formed, must be slowly dried, and then properly baked in the kiln.

Black Lead Crucibles are made of 2 parts graphite, and 1 of fire-clay, mixed with water into a paste, pressed in moulds, and well dried, but not baked hard in the kiln. This compound forma excellent small or portable furnaces.