Note 180 — Chapter IV · (XI.)

The subject of the composition of bronze and of other alloys of copper is a complicated one, for the mixtures specified or established by analysis are very varied. Normally speaking, bronze is a mixture of copper with about ten per cent. of tin, brass of copper with twenty to forty per cent. of zinc. Vasari’s proportions for bells and for cannon are pretty much what are given now. In the Manuel de Fondeur (Manuels Roret) Paris, 1879, II, p. 94, eight to fifteen per cent. of tin are prescribed for cannon, fifteen to thirty per cent. for bell metal, the greater percentage of tin with the copper resulting in a less tough but harder and so sharper sounding metal. It will be noted however that for statuary metal Vasari specifies a mixture not of copper and tin but of copper and brass, that is, copper and zinc. Brass is composed of, say, twenty-five per cent. of zinc and seventy-five per cent. of copper, so that a mixture of two thirds, or sixty-six per cent., of copper with one third, or thirty-three per cent., of brass would work out to about ten parts of zinc to ninety of copper, and this agrees with classical proportions. The Greeks used tin for their bronzes, but various mysterious ingredients were supposed to be mingled in to produce special alloys. The Romans used zinc, or rather zinciferous ores such as calamine, with or in place of tin, and this is the tradition that Vasari follows.

A recent analysis of the composition of the bronze doors at Hildesheim, dating from 1015 A.D., gives about seventy-six parts copper, ten lead, eight tin, four zinc; and of the ‘Bernward’ pillar ascribed to about the same date, seventy copper, twenty-three tin, and five lead. These differences may surprise us, but metal casting in those days was a matter of rule of thumb, and we may recall Cellini’s account of his cramming all his household vessels of pewter into the melting pot to make the metal flow for casting his ‘Perseus.’