"If the final work is to be in marble, or bronze, or only in plaster, the next process after finishing the model is to mould it, in preparation for its being reproduced in a material that will bear moving about without risk of injury to the design. This is done by covering it with a mixture of plaster of Paris with water, which quickly sets or becomes consistent, forming a hard and thick coating over the whole. The clay is then carefully picked out, and an exact matrix, or form, remains. This is washed clean, and the interior is then brushed over with any greasy substance, usually a composition of soap and oil, to prevent the plaster with which it is next to be filled adhering too firmly to it. The fresh plaster is mixed to about the consistency of cream and then poured into the mould, which is gently moved about till the inner surface is entirely filled or covered, so that all parts may be reached. The thickness or substance of the coating depends upon the size of the work and the degree of strength required. "When the newly introduced plaster is set the mould is carefully knocked away with chisels, and a true cast appears beneath, giving an entire fac-simile of the original model. Some skill is required in making moulds, in order to provide for projecting parts and under-cuttings; practice alone can teach the artist how to deal with those difficulties when they occur. The above general instructions sufficiently explain the ordinary processes of moulding and casting in plaster. "In metal-casting or founding great attention must be paid to the strengthening of the parts to bear the weight of the metal; but the principle described in plaster-moulding applies also to the preparation for metal-casting. The mixture of metals to form bronze, the proper heating of the furnace, burning and uniting parts, chasing and other processes of founding cannot be fully described in this place. They belong to a distinct practice, and to be well understood must be studied in the foundry.