In making a crucible with a quantity of plumbago dust, mix the plumbago with an equal weight of fireclay, and add water while kneading to form a stiff dough. Keep this in a cool place for a few days, and work it from time to time, when it will become less sticky and more plastic; the clay should be almost too stiff to work lay the hand when it is ready for moulding. For this, use au iron mould with a plug attached to a handle. The mould should be filled with the clay and the plug hammered in, to form the hollow of the crucible. It is kept in a warm place for a few days, when the crucihle will leave the mould, and may be turned out. It is dried in a warm place for several weeks, and gradually heated when it is used for the first time.