The best crucibles are made of a pure fire clay, mixed with
finely ground cement of oil 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 a kiln.
Black Lead Crucibles are made of two parts of Graphite and one of
Fire Clay, mixed with Water into a paste, pressed in moulds, and well
dried, but not baked hard in the kiln. This compound forms excellent
small or portable furnaces.