Tin Bronze

Bronzes have an extraordinarily long history of use by human civilizations. The discovery of bronze is considered to be of such importance to society that a whole period of prehistory is named after the material. Prior to the discovery of bronze, copper was the most widespread metal, but it was too soft to hold up to aggressive use, for example as weaponry or tools, and quickly lost its colour, sheen and sharp edge. The hardening effects of impurities in copper ore were first discovered as far back as the 4th millennium BC, and in a number of ancient civilisations including Mesopotamia, Sumer, Indus, China and the Aegean.

In fact, many of the early accidental bronzes were arsenic-bronzes, not tin-bronzes, which make s sense, as arsenic minerals are far more common than tin minerals. Whilst arsenic additives also hardened copper and made it more ductile, they had the nasty side-effect of killing off early metal smiths, as arsenic produces highly toxic fumes when roasted. The manufacture of bronze using tin was less dangerous and more predictable since the main ore of tin (cassiterite) has a very high and consistent tin content, whereas arsenic oxides can be very variable. Because this ore is often scarce in areas where copper is plentiful, the development of bronze metallurgy led to international trade on an unprecedented scale.

Because of its relatively low melting point compared to iron and steel, its resistance to corrosion and its attractive golden-brown colour, bronze is often used to cast monumental statuary, including the four lions at the base of Nelson’s column in Trafalgar Square. Most bronze alloys also expand slightly just before they set, taking on fine details in a mould. This sample has an almost quartz-like upper surface where it has been polished, and the crystalline structure of the metal can be seen on its face.