"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.

"If the model—now reproduced in plaster—is to be copied in marble or stone, the first step is to procure a block of the required size. Two stones, called scale-stones, are then prepared, upon one of which the model or plaster cast is placed, and upon the other the rough block of marble. The fronts of these stones have figured marks or 'scales,' to use the technical term, exactly corresponding. An instrument capable of being easily moved, and which is fitted up with socket-joints and movable arms, is then applied to the scale-stone of the model, and a projecting point or 'needle' is made to touch a particular part of the model itself. This is carefully removed to the scale-stone of the rough block, and the marble is cut away till the 'needle' reaches so far into the block as to correspond with the 'point' taken on the model. A pencil-mark is then made to show that the point is found and registered. This process is repeated all over the model and block, alternately, till a rough copy or shape of the model is entirely made. These 'pointing' machines are not always precisely alike in their forms, but the principle upon which they act is exactly similar in all. The statue being thus rudely shaped out, the block is placed in the hands of a superior workman, called a 'carver,' who, having the plastic model near at hand to refer to, copies the more minute portions of the work by means of chisels, rasps, and files, the pencil-marks made by the 'pointer' showing him the precise situation of the parts and the limit beyond which he is not to penetrate into the marble. When the carver has carried the work as far as the sculptor desires, he proceeds himself to give it the finishing touches, improving the details of form and expression, managing the different effects produced by two different materials—one, the plastic model, being opaque; the other, the marble, being considerably diaphanous; giving the proper varieties of texture in the flesh, hair, and drapery, and, more especially, harmonizing the whole.

"The rich quality of surface that appears more or less in works of marble is produced by rubbing with fine sand or pumice-stone and other substances, and the ancients appear to have completed this part of their work by a process which is called 'circumlitio,' and may mean not only rubbing or polishing, but applying some composition, such as hot wax, to give a soft, glowing color to the surface. Many of the ancient statues certainly exhibit the appearance of some foreign substance having slightly penetrated the surface of the work to about one eighth of an inch, and its color is of a warmer tint than the marble below it; a process, be it observed, quite distinct from and not to be confounded with polychromy, or what is usually understood by painting sculpture with various tints, in imitation of the natural color of the complexion, hair, and eyes. Its object, probably, with the ancients as with modern sculptors, has been simply to get rid of the glare and freshness of appearance that is sometimes objected to in a recently finished work, by giving a general warmth to the color of the marble."

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