BRONZING. A combination of metals which has received the name of bronze was employed by the ancients in the fabrication of different utensils, and in casting busts, statues, and other subjects, either larger or smaller than life. The Egyptians, Greeks, and Romans, nations which subsisted long and were familiar with the most refined state of the arts, used this compound metal in the greater part of the decorations of those magnificent temples and palaces whose ruins only have remained to later eras. But amidst the general wreck there are still some fragments preserved, which indicate the perfection which had been attained in the employment of bronze. The wealth of some ancient cities was estimated by the number of their brazen statues; and Delphos, Athens, and Rhodes, are reported to have each possessed three thousand. Some distinguished Romans adorned the public edifices of their city in this manner; and so strong a propensity was excited for multiplying works of this kind, that an observation became current, that in Rome the people of brass were not less numerous than the Roman people. It has been remarked, that the works which we now execute in iron or steel were little known to the ancients; that their arms and armour were usually of brass, or the compound now alluded to; and that a set of surgeon’s instruments consisting entirely of bronze was discovered at Pompeii.

Bronze is extremely hard, sonorous, more brittle than brass, and more fusible than copper, from which, and its not being liable to tarnish, it is peculiarly adapted for casts of statues. Various nations have compounded the metals employed in different proportions. The Egyptians are said to have taken two thirds of brass and one third of copper. According to Pliny, the bronze of the Grecians was formed in the same way, with the addition of one tenth part of lead and a twentieth of silver; which proportions were adopted by the Romans. In modern times bronze is generally composed of two thirds of copper and one third of brass, and sometimes small quantities of lead and zinc have been added. These latter render the cast more compact and brilliant; and the combination of different substances occasions the readier fusibility of the whole than when separate. The ancient bronzes, however, present a difference in appearance and composition from those executed’by the moderns, and the fact is ascertained in respect to the metallic proportions, by skilful chemists on analysis. An illustration of this fact is sometimes given in the four celebrated horses of bronze, supposed to be the work of Lysippus, a Greek artist; which were brought from Venice, by command of Bonaparte, to the Thuilleries at Paris, and, on the fall of that extraordinary man, restored to their original position.

The casting of bronze statues is a nice and difficult art, requiring long experience and the judicious management of a great apparatus. An exact model must be made of the subject to be cast, and nicely coated over with wax not less than an inch thick, on which the artist works the impression meant to be taken. A mould is then formed, consisting of several hollow pieces of wood or other resisting substance, filled with a mixture of clay and sand, which is applied to the model, in order that its outline may be received. The mould being united together, is perforated by a number of channels, and the melted metal being discharged from a furnace by means of these into the interior, thus produces the cast. When cold, the external covering is taken off, and the subjects appear as if covered with spines, which are the channels filled with metal: these arc removed by saws, files, and chisels; and any imperfections on the surface being corrected, the whole is completed. But this in detail is a tedious, laborious, and expensive process; and the difficulty of producing beautiful works in bronze conspires to give them a high value in the estimation of the lovers of the arts. In general, the natural colour of the composition remains unaltered, and with the lapse of time tends to black, or particular shades of green; but some artists render it black artificially", or give it a green colour from the first. It is the delicacy of the workmanship, however, that constitutes the value of bronzes, not the colour, because it is the former alone which constitutes the difficulty, and calls for the skill of the artist. Colossal figures are sometimes obtained in bronze; but more usually, when of very large dimensions, they are formed by the union of several pieces, and are hollow within; as is also the case with some of those of smaller size. Considerable premiums have been offered by the Society for the Encouragement of Arts, for promoting the execution of bronze figures in England, but few have been claimed. Nevertheless, British artists have produced several very creditable works, if we take the low condition of sculpture in view, but, either from wantof skill or practice,neither the bronzes of this island nor those of the Continent can rival the masterpieces of antiquity. Perhaps it is only the best specimens which are preserved, and many of inferior note have been allowed to decay, or cease to attract attention; an in this way we may partly account for our own inferiori j∙
[7:5:589]

The substances on which bronzing is employed are either metals, wood, ivory, clay, or plaster; but more general preference is given to wood or plaster. The colours are of various shades and intensity; their composition and application being in a great measure arbitrary, according to the will of the artist. This art is nothing but a species of painting, far from the most delicate kind; and, when applied to plaster figures, may be done either with or without cement, the latter rendering it more durable. One principal ingredient in bronzing is gold-powder, for the preparation of which the following receipt is given. A quantity of leaf-gold is ground with virgin honey on a stone, until the texture of the leaves be completely broken, and their parts divided to the most minute degree. The mixture of gold and honey is then removed from the stone and put into a basin of water, whereby the honey may be melted, and the gold freed from it; and the basin is allowed to stand at rest until the gold subsides. When it does so, the water is poured off, and fresh quantities are added, until the honey be entirely washed away; after which the gold is put in paper, and dried for use. This is the true gold powder; besides which, there is another, called German gold, in common use; and also a third, called aurum mosaicum, or musicum, greatly employed in bronzing, and which is thus prepared. A pound of tin, seven ounces of flour of sulphur, half a pound of purified quicksilver, and the same quantity of sal ammoniac, are taken as the necessary ingredients. The tin being melted in a crucible, the quicksilver is added to it; and, when this mixture is cold, it is reduced to powder, and ground with the sal ammoniac and sulphur, until the whole be thoroughly mixed. They are then to be calcined in a matrass, and die sublimation of the other ingredients will leave the tin converted into the aurum mosaicum, which is found at the bottom of the glass like a mass of bright flaky gold powder. Should any black or discoloured particles appear, they must be removed. The sal ammoniac used here must be very white and clean, and the mercury quite pure, and unadulterated with lead. These colours are commonly employed in bronzing; but when a shade more of a red, resembling copper, is required, it can easily be obtained by grinding a very small quantity of red lead along with them. Copper powder may be procured by dissolving filings or slips of that metal with nitrous acid in a receiver. When the acid is saturated the slips are to be removed; or, if filings be employed, the solution is to be poured off from what remains undissolved. Small iron bars are then put in, which will precipitate the copper from the saturated acid, in a powder of the peculiar appearance and colour of copper; and the liquid being poured from the powder, this is to be washed clean off the crystals by repeated levigations. In addition to these compounds, we may name gold size, which is of particular use in bronzing and several other branches of the arts. This is prepared from a pound of linseed oil, with four ounces of gum animi. The latter is gradually supplied in powder to the oil, while boiling; and it is necessary that it should be stirred with every successive dose, until the whole be dissolved and incorporated with the oil. The mixture is still allowed to continue boiling, until a small quantity, when taken out, appears of a thicker consistence than tar, and the whole being then strained through a coarse cloth, is put aside. When used, it must be ground with as much vermilion as will render it opaque, and, at the same time, diluted with such a quantity of oil of turpentine as will bring it to a proper consistence for working freely with the pencil.

In regard to the operation of bronzing itself, if a cement is to be used, the powders now described may be mixed with strong gum water or isinglass, and laid on the subject with a brush or pencil; in doing which, some artists recommend beginning at the bottom and proceeding upwards. By a different process, gold size, prepared with a due proportion of turpentine, may be taken, and the subject covered with it; then being allowed to dry very nearly, but still preserving a certain clamminess, a piece of soft leather wrapped round the finger is dipped in the powder, and rubbed over the work; or, what is judged preferable, it may be spread with a soft camel-hair pencil. The whole, now covered, must be left to dry, and the loose powder then cleared away by a hair pencil also. Here the principal nicety consists in ascertaining the proper period of dryness for applying the powder, as much of the effect depends on it. But this method of bronzing is esteemed better, because the gold size binds the powders to the ground, without any hazard of their scaling or rubbing off, which sometimes happens when gum or isinglass is employed. The precise tint of bronzing is regulated by taste; and, indeed, a very perceptible difference appears both in ancient and modern statues, resulting either from age or the metallic proportions.

Bronzing on wood may be effected by a particular process, somewhat varying from the general rules. Prussian blue, patent yellow, raw umber, lamp-black, and pipe-clay, are ground separately with water, on a stone, and as much of them as will make a good colour put into a small vessel three fourths full of size, not quite so strong as what is called clean size in gilding. This mixture is found to succeed best on using about half as much more pipe-clay as of the rest; but this depends on taste and fancy in preferring a peculiar tint. The wood being previously cleaned and smoothed, and coated with a mixture of clean size and lamp-black, receives a new coating with the preceding ingredients, twice successively, having allowed the first to dry: afterwards the bronze-powder is to be laid on with a pencil, and the whole burnished or cleaned anew, observing to repair the parts which maybe injured by this operation. Next, the work must be coated over with a thin lather of Castile soap, which will take off the glare of the burnishing, and afterwards carefully rubbed with a woollen cloth. The gangrenous appearance of the cavities is effected by slightly wetting them with a camel-hair pencil dipped in the lather, and then sprinkling them with a little dust of verditer gum. The superfluous powder may be rubbed off when dry.

In bronzing iron, the subject should be heated to a greater degree than the hand can bear, and German gold, mixed with a small quantity of spirit of wine varnish, spread over it with a pencil. Should the iron be already polished, it is necessary to heat it well and moisten it with a linen rag wet in vinegar, on purpose to obscure the glare, that the bronze-powder may be sufficiently incorporated with the surface. There are other methods of accomplishing the same object, as by employing some coloured mordant, when the iron is not to be exposed to heat, and spreading the bronze over the mordant, when half dry, with a pencil. Bronze is injured by humidity; and it is said not to preserve its proper quality beyond ten years; but it may be renewed, in which case the subject must be completely cleaned.

There is an analogous method of silvering casts of plaster of Paris, and other substances, which is also called bronzing, and conducted after the manner above described ∙ but it is not in general repute.

Conjectures have been entertained, that artists originally resorted to bronzing solely for the purpose of correcting the glare of colours; but this is exceedingly improbable ∙ and it is certainly unnecessary to seek farther than the inducement of easily imitating metallic figures esteemed by the curious. This art has of late years come into very general use, and has received many improvements.
[7:5:590]