Classical Studies 2700B

BRONZE

[We are about 5 to 7 minutes behind where we should be. I shall, accordingly, on Tuesday deal first with the last part of the Introduction to metal and then go to our topic of the day. CLM]

Slides: reconstruction of early copper mining and smelting at Timna (in Negev desert) at c. 3,800 BC. Ore mined is (green) Malachite, then crushed to consistency of gravel. Temp. required to reduce this ore is at least 815° C, and higher is desirable. So, circular fireplaces partly sunk into ground. Combination of hard-wood charcoal (from acacia trees) and ground-up ore; temp. raised by workers blowing through tubes fitted with tuyères. Small amounts of copper found amid blackish slag. Casting of copper was a separate process; evidence from a village called Abu Matar, c. 160 km. N. of Timna (slides). By 1,200 BC operations at Timna on v. large scale, carried out by Egyptian government; by this time output was high—one man could mine enough ore in a day to produce 8 lb (c. 3.6 kg.) of smelted copper. New type of “tappable” furnace made this high output possible; it ran non-stop for several days.

BRONZE: modern bronze can range from 3% to 25% tin, though small amounts of lead and zinc usually added as well. Earliest bronze was combination of copper and arsenic (As), the latter of which eliminates gases in copper and makes for a better casting. By 3,500 BC these effects were being noticed and ores containing copper and arsenic were being deliberately favoured, but process was hit-or-miss and no control over percentages of each. By about 3,000 BC tin (Sn) was favoured substitute for arsenic (why was this avoided?) A hammered 90% copper + 10% tin bronze comes close in hardness to mild steel. But not much, if any, tin in Near East; so great expansion of trade routes; in Caucasus area of modern Armenia malachite and the tin ore cassiterite often occur together; true bronze may have first been produced there.

By 2,000 BC with great trade networks, bronze production was widespread and in S. Mesopotamia the Sumerians could control exactly the percentages of copper and tin in their bronze (implications of this). By 1800 BC Bronze Age well underway in central Europe, and large-scale mining operations in the Austrian Alps (Mitterberg) by 1200 BC: this complex estimated to have produced about 13,000 tonnes of smelted copper between 1200and 800 BC. Great range of artefacts produced— wire, sheets, and castings. As “case study” of advanced bronze-working techniques, examination of products from ancient China in period of Shang dynasty (c. 1600-1100 BC), with capital at An Yang (c. 6,000 ha) in N. Honan province. Early history of metal-working in China v. obscure—perhaps the evidence is lacking, as yet. But in early Chinese pottery, kilns were very hot, c.1200° C. Shang bronzesmiths went straight into casting and made great range of luxury goods for wealthy noble class. Exx (slides) of such bronzes and explanation of how they were produced.

Other metal-working techniques: a) flat-chasing, with hammer and punch with rounded edge; b) raising, where plain, cast, flat disc of ductile metal, like gold or silver, is transformed into cup or bowl; c) embossing, where hammers and punches work on metal sheet from behind; (continued in next lecture’s notes…)