BRONZE. A material used for casting statues, groups, &c., in a mould similar in principle to that wherefrom all plaster casts are produced. From the extraordi nary dimensions which involve the chief differences between the operations of cast ing in brass and plaster, much intelligence and care on the part of the sculptor is necessary to produce the fac-simile of the work on which his labor has been expen ded. The material employed for the pur pose is a compound chiefly consisting of copper, tin, and other metals. The pro cess of procuring the cast depends on circumstances requiring much nice ar rangement.
Bronze is a compound metal, consisting of copper and tin, to which sometimes a little zinc and lead are added. The alloy is much harder than copper, and was em ployed by the ancients to make swords, hatchets, &c., before the method of ma king iron was understood. The art of casting bronze statues may be traced to the most remote antiquity : but it was first brought to a certain degree of re finement by Theodorus and Rcecus of Samos about 700 years before the Chris tian era, to whom the invention of model ling is ascribed by Pliny. The ancients were well aware that by combining cop per with tin a more fusible metal was obtained, that the process of casting was therefore rendered easier, and that the statue was harder and more durable; and yet they frequently made them of cop per nearly pure, because they possessed no means of determining the proportions of their alloy, and because by their mode of managing the fire, the copper became refined in the course of melting, as has happened to many founders in our own days. It was during the reign of Alex ander that bronze statuary received its greatest extension, when the celebrated artists Lysippus succeeded by new pro cesses of moulding and melting to multi ply groups of statues to such a degree that Pliny called them the mob of Alex ander. Boon afterwards enormous bronze colossuses were made to the height of towers, of which the isle of Rhodes pos sessed no less than one hundred.
The Roman consul Mutianus found 8,000 bronze statues at Athens, 3,000 at Rhodes, as many at Olympia and at Del phi, although a great number had been previously carried off from the last town.
In forming such statues the alloy should be capable of flowing readily into all the parts of the mould, however minute ; it should be hard, in order to resist acci dental blows, be proof against the influ ence of the weather, and be of such a na ture as to acquire that greenish oxidized coat upon the surface which is so much admired in the antique bronze. The chemical composition of the bronze alloy is a matter therefore of the first moment. The brothers Keller, celebrated founders in the time of Louis the Fourteenth, whose chefs d'oeuvre are well known, di rected their attention towards this point, to which too little importance is attached at the present day. The statue of Desaix, in the Place Vendome in Paris, is a noted specimen of most defective workman ship from mismanagement of the alloys of which it is composed.
On analyzing separately specimens ta ken from the bas-reliefs of the pedestal of this column, from the shaft, and from the capital, it was found that the first contained only 6 per cent, of the alloy, and 04 of copper, the second much less, and the third only 0-21. It was there fore obvious that the founder, unskilful in the melting of bronze, had gone on progressively refining his alloy by the oxidizement of the tin, till he had ex hausted the copper, and that he had then worked up the scoria in the upper part of the column. The moulding of the seve ral bas-reliefs was so ill-executed that the chisellers employed to repair the faults, removed no less than 70 tons of bronze, which was given them, besides 300,000 francs for their work.
The alloy most proper for bronze med als, which are to be afterwards struck, is composed of from 8 to 12 parts of tin, and from 92 to 83 of copper ; to which if 2 or 3 parts in the hundred of zinc be added, they will make it assume a finer bronze tint. The medal should be sub jected to three or four successive stamps of the press, and be softened between each blow by being heated and plunged in cold water.