Subjects.--Sculpture, in its most general sense, is the art of producing resemblances of visible forms, out of solid materials. The required shapes are produced by carving, when the material is solid and brittle; and to this sense the term sculpture is sometimes limited. They are also formed by modelling, when the material is soft; and by casting, when it is liquid or fusible. The productions of this art are known under various denominations, according to their character and subject. Of these, the most important are statues, which are entire resemblances of living objects. Busts consist of the upper portions of statues. Bas-reliefs, in the common acceptation of the term, are partial sculptures, or lateral views of figures, raised on a plane surface. Their different degrees of prominence are distinguished by the Italians, under different names. These are, alto relievo, or high relief, when the figures are nearly complete, or appear to issue from the back-ground; mezzo relievo, or middle relief, in which they are half raised from the surface; and basso relievo, low relief, or bas-relief properly so called, when the figures have not the prominence which their outline requires, but appears as if compressed. The principal objects of sculpture, are vases, armatures, or trophies, and the decorative parts of architecture.

Modelling.--Before any object is executed in stone, it is the practice of sculptors to complete a representation of their design, by modelling it in clay, or some other soft material. The genius of the artist is displayed altogether in the model; for the process of afterwards copying the model in stone, is chiefly mechanical, and may often be executed by another person, as well as by the sculptor himself. When a clay model is undertaken, if the proposed figure be large, a frame of wood or iron is erected to give support to the limbs and different parts of the figure. Upon this frame, a proper quantity of wet clay is distributed, and wrought into the form of the intended statue. The moulding of the clay is performed with the hands, and with various instruments of wood and ivory. When the model is completed, copies may be taken from it, either by casting them in plaster, or in metal; or by chiselling them in marble.

Casting in Plaster.--Copies are most frequently taken, both frOm new models, and from old statues, by casting them in plaster. For this purpose, a mould in plaster is first made from the surface of the statue, or figure, itself; and this mould is afterwards used to reproduce the figure by casting. Plaster is prepared for use by pulverizing common gypsum, and exposing it to the heat of a fire until its moisture is wholly expelled.[A] While in this dry state, if it be mixed with water to the consistence of cream or paste, it has the property of hardening in a few minutes, and takes a very sharp impression. The hardness afterwards increases by keeping, till it approaches the character of stone.

Moulds are formed in the following manner. The statue or figure to be copied, is first oiled, to prevent it from cohering with the gypsum. A quantity of liquid plaster sufficient for the mould, is then poured on, immediately after being mixed, and is suffered to harden. If the subject be a bas-relief, or any figure which can be withdrawn without injury, the mould may be considered as finished, requiring only to be surrounded with an edging. But if it be a statue, it cannot be withdrawn, without breaking the mould; and on this account it becomes necessary to divide the mould into such a number of pieces, as will separate perfectly from the original. These are taken off from the statue, and when afterwards replaced, or put together, without the statue, they constitute a perfect mould. This mould, its parts having been oiled to prevent adhesion, is made to receive a quantity of plaster, by pouring it in at a small orifice. The mould is then turned in every direction, in order that the plaster may fill every part of the surface; and when a sufficient quantity is poured in to produce the strength required in the cast, the remainder is often left hollow, for the sake of lightness, and economy of the material. When the cast is dry, it is extricated by separating the pieces of the mould, and finished by removing the seams and blemishes with the proper tools.[B] If the form or position require it, the limbs are cast separately and afterwards cemented on.

[A] The heat requisite for this purpose must be greater than that of boiling water. Care must be taken not to raise the heat too high, as in that case the sulphate of lime would be decomposed.

Moulds and busts are obtained in a similar manner from living faces, by covering them with new plaster, and removing it in pieces as soon as it becomes hard. It is necessary that the skin of the face should be oiled, and, during the operation, the eyes are closed, and the person breathes through tubes inserted in the nostrils.

Elastic moulds have been formed by pouring upon the figure to be copied, a strong solution of glue. This hardens upon cooling, and takes a fine impression. It is then cut into suitable pieces and removed. The advantage of the elastic mould is that it separates more easily from irregular surfaces, or those with uneven projections and under cuttings, from which a common mould could not be removed without violence.[A]

Architectural models, and other complex pieces of workmanship, are made by casting the constituent parts separately, and afterwards cementing them together. If the form of the parts is complicated, a mould is required which can be taken to pieces to extract the cast. The cementing of the parts is performed by a thin mixture of plaster and water, recently made, and it is necessary that the surfaces to be joined should be thoroughly wet, before the cement is applied to them.

For small and delicate impressions, which are merely in relief, melted sulphur is sometimes used, also a strong solution of isinglass in proof spirit. The latter material has the advantage that it is not brittle when dry, but possesses a consistence like that of horn. Both substances yield very accurate and sharp impressions.

Bronze Casting.--Statues intended to occupy situations in which they may be exposed to violence, are commonly made of bronze. This material resists both mechanical injuries, and decay from the influence of the atmosphere. The moulds in which bronze statues are cast, are made on the pattern, out of plaster and brick dust; the latter material being added to resist the heat of the melted metal. The parts of this mould are covered on their inside with a coating of clay, as thick as the bronze is intended to be. The mould is then closed, and filled on its inside with a nucleus, or core of plaster and brick dust, mixed with water. When this is done, the mould is opened, and the clay carefully removed. The mould with its core, are then thoroughly dried, and the core secured in its central position by short bars of bronze which pass into it through the external part of the mould. The whole is then bound with iron hoops, and when placed in a proper situation for casting, the melted bronze is poured in through an aperture left for the purpose. Of course, the bronze fills the same cavity which was previously occupied by the clay, and forms a metallic covering to the core. This is afterwards made smooth by mechanical means.

[A] See a paper by Mr. Fox, republished in the Franklin Journal, vol. iii.

Practice of Sculpture.--To execute a statue in marble, which shall exactly correspond to a pattern or model, is a work of mechanical, rather than of inventive skill. It is performed by finding, in the block of marble, the exact situation of numerous points corresponding to the chief elevations and cavities in the figure to be imitated, and joining-these by the proper curves and surfaces, at the judgement of the eye. These points are found, by measuring the height, depth, and lateral deviation of the corresponding points in the model; after which, those in the block are found by similar measurements. Sometimes the points are ascertained, by placing the model horizontally under a frame, and suspending a plumb-line successively from different parts of the frame, till it reaches the parts of the figure beneath it. Sometimes an instrument is used consisting of a movable point, attached by various joints to an upright post, so that it may be carried to any part of the statue, and indicate the relative position of that part in regard to the post. Machines have also been contrived for cutting any required figure from a block, the cutting instrument being directed by a gauge which rests upon the model in another part of the machine.

Marble is wrought to the rough outline of the statue, by the chisel and hammer, aided by the occasional use of drills and other perforating tools. It is then smoothed with rasps and files, and when required, is polished with pumice-stone and putty. The hair of statues is always finished with the chisel; and for this object, very sharp instruments with different points and edges are necessary The ancient sculptors appear to have relied almost wholly upon the chisel, and to have used that instrument with great boldness and freedom, such as could have been justified only by consummate skill in the art. The moderns, on the contrary, approach the surface of the statue with great caution, and employ safer means for giving the last finish. Some of the most celebrated antique statue such as the Laocoon, the Apollo Belvidere, and Venus de Medicis, are thought to have been finished with the chisel alone.

Materials.--Although marble has been the common material of sculpture, both in ancient and modern times, yet other substances have been occasionally made subjects of the chisel. Statues of porphyry, granite, serpentine, and alabaster, are found among the remains of antiquity. Other materials of a less durable kind, were also employed. Some of the principal works of Phidias were made of ivory and gold, particularly his colossal statues of Jupiter Olympius, and Minerva, at Athens.

Objects of Sculpture.--In sculpture, as in the other imitative arts, two ends propose themselves to the skill of the artist. One consists in the imitation of a particular object, in which case the art of the sculptor can be expected only to equal, but not to surpass, his original. The other consists in new combinations of excellence, and in the invention of forms and expressions, which are not known to exist together in nature, but are imbodied in the imagination of the artist. Beauty in objects thus conceived, constitutes the beau ideal in art, to attain which, has ever been the ambition of cultivators of the fine arts. In statuary, the specimens which have descended to us from the ancient Greeks, are by universal consent admitted to be the most perfect designs of beauty, and furnish the common models for study and imitation, at the present, as in all former ages.

Gem Engraving.--The art of cutting precious stones, is more properly a species of sculpture, than of engraving. The hardness of these stones renders it impossible to operate on them by the strongest steel instruments. They are therefore wrought in a slow manner, by grinding them away upon the surface of a wheel, commonly made of metal, and covered with the grit, or fine powder, of some hard substance. The diamond can only be ground, or cut, with its own dust. Rubies, agates, emeralds, &c, are cut and polished with emery or tripoli, in fine powder. Lapidaries make use of small wheels, balls, and drills, of various forms, made of iron, or copper, which revolve with great rapidity, and act upon the stone through the medium of the pulverized material on their surface. They also use wires covered with emery, for the purpose of sawing plates.

The imitative designs, which are cut upon hard stones, are chiefly of two kinds. The first of these are cameos, which are little bas-reliefs or figures, raised above the surface. They are commonly made from stones, the strata of which are of different colors, so that the raised figure is of a different color from the ground to which it is attached. Varieties of agate, carnelian, onyx, &c, are made use of for this purpose. Sometimes several successive strata of different colors, are so wrought as to produce the appearance of painting. A cheaper kind of cameos are made from marine shells. These, having lime for their basis, may be scratched with steel, or corroded with acids. Intaglios are the second kind of engraved gems. They differ from cameos in having the figure cut into, or below, the surface, so that they serve as seals to produce impressions in relief upon soft substances.

Mosaic.--Mosaics are imitations of paintings made by combining together an infinite number of minute stones of different colors, and cementing them on a plane surface. In the most costly mosaics, precious stones have been cut, and arranged to produce this effect. But in common works of this art, enamels of different colors, manufactured for the purpose, are the material employed. The enamel is first formed into sticks, from the ends of which, pieces of the requisite size are cut or broken off. These are confined in their proper places upon a plate of metal or stone, by a cement made of quicklime, pulverized limestone, and linseed oil. After the whole has adhered, it is allowed to dry two months, and is then polished with a flat stone and emery.[A] Inlaid works of agate, and other costly stones, are executed on the same principle as mosaic; except that the stones are larger, and cut to the shape of different parts of the object to be represented; whereas in mosaic, the pieces are of the same size and shape. The opus reticulatum of the ancients, with which columns and walls were sometimes incrusted, is found to consist of small stones, of a pyramidal form, the apex of which is imbedded in mortar, while the base, which is polished, forms the outer surface.

Scagliola.--This name is given at Rome, to a sort of artificial inlaid work, composed of plaster, but resembling stone. For works of this kind, gypsum, dried and powdered, is mixed with a solution of glue, and spread on a tablet for the ground of the picture. Cavities of the form intended in the design, are then made in it with an engraving tool. These are successively filled up with portions of plaster of different colors, so managed as to produce the effect of painting. In this way, buildings, and various natural objects, are represented. The surface is finely polished, by rubbing it with different powders, and, where the ground is white, with rushes.

[A] One of the largest mosaics which has been executed, is a copy of Leonardo da Vinci's celebrated picture of the Last Supper. It measures twenty-four feet by twelve, and employed eight or ten artists for eight years. It was executed under the direction of Raffaelli, at Milan, by order of the French government.--Cadell.

WORKS OF REFERENCE.--WINCKELMANN, Histoire de l'Art chez les Anciens, 3 vols. 4to. tr. 1802;--MILLIN, Dictionnaire des Beaux Arts, 3 vols. 8vo. 1806;--FLAXMAN'S Lectures on Sculpture, large 8vo. 1829;--REES'S Cyclopaedia;--Works of VASARI;-- QUATREMERE DE QUINCY---CICOGNARA---VISCONTI, &c.;--- Travels and Works of CLARKE,--EUSTACE,---CADELL,--DODWELL,--STUART,--ELGIN, &c. &c.