BRONZE is essentially a compound of cop per and tin, which metals appear to have been among the earliest known. Copper is not un frequently found in its metallic state, and fit for immediate use; and tin, though not so met with, often occurs near the surface, and its ore is easily reduced. These metals, though neither of them possesses the hardness requi site for making instruments either for domes tic or warlike purposes, appear to have been early found capable of hardening each other by combination ; the bronze, which is the re sult of this combination, consisting of different proportions of them, according to the purposes to which it is to be applied.
Bronze is always harder and more fusible than copper ; it is highly malleable when it contains 85 to 90 per cent. of copper ; temper ing increases its malleability ; it oxidises very slowly even in moist air, and hence its appli cation to so many purposes. The density of bronze is always greater than that of the mean of the metals which compose it : for example, an alloy of 100 parts of copper and 12 parts of tin is of specific gravity 8.80, whereas by calculation it would be only 8.03.
The green hue that distinguishes ancient bronzes is acquired by oxidation and the com bination with carbonic acid ; and the moderns, to imitate the effect of the finer antique works, sometimes advance that process by artificial means, usually by washing the surface with an acid. Vasari alludes to this practice among the artists of his time, and to the means they adopted to produce a brown, a black, or a green colour in their bronze.
Bronze was well known to the ancients. Among the remains of bronze works of art found in Egypt none are of large dimensions. Many specimens of bronze works found in In dia are doubtless very ancient. In the time of Homer, arms, offensive and defensive, are always described as being made of bronze, or perhaps copper alone, which it is possible they had some means of tempering and hardening. The art of casting statues seems to have been first practised in Asia Minor, Greece, properly so called, being then probably too uncivilised to undertake such works. The first and most simple process, among the Greeks, appears to have been hammer-work ; in which lumps of the material were beaten into the proposed form ; and, when the work was too large to be made of one piece, several were shaped, and the dif ferent parts fitted and fastened together by means of pins or keys.
The art of metal-casting in regular moulds was undoubtedly known very early, though its adoption in European Greece is probably of a comparatively late date. Its progress was evidently marked by three distinct stages. The first was beating out the metal, either as solid hammer-work or in plates. The next was casting it into a mould or form, the statue being of course made solid. The last stage was casting it into a mould, with a centre or core to limit the thickness of the metal. Bronze-casting seems to have reached its perfection in Greece about the time of Alexander the Great. The ancient statuaries seem to have been extremely choice in their selection and composition of bronze ; and they seem also to have had a method of running or welding various metals together, by which they were enabled to produce more or less the effect of natural colour. Some works are de scribed that were remarkable for the success which attended this curious and, to us, unat tainable process. They also tinted or painted their bronze with the same view of more closely imitating nature. Pliny states that there were three sorts oftheCorinthian bronze; the first, called canclidum, received its name from the effect of silver which was mixed with the copper ; the second had a greater propor tion of gold; the third was composed of equal quantities of the different metals.
The Romans never attained any great emi nence in the arts of design. Their earliest statues were executed for them by Etruscan artists. Rome, however, was afterwards filled with a prodigious number of works of the best schools of Greece ; and artists of that country, unable to meet with employment at home, settled at Rome. Zenodorus executed some magnificent works in the time of Nero. But Pliny, who lived in the reign of Vespasian, la ments the decline of the art, and the want of skill of the artists, in his time. The practice of gilding bronze statues does not seem to have prevailed till taste had much deteriorated. The practice of art among the Romans declin ing rapidly, and with but few interruptions, ceases to interest us about A.D. 200. In the beginning of the thhteenth century, at the taking of Constantinople, we read that some of the finest works of the ancient masters were destroyed for the mere value of the metal. Among the few works saved are the celebrated bronze horses, which now decorate the exterior of the church of St. Mark at Venice.