Bronze

Earliest Metals ones which are found in relatively pure forms
• Gold
• Copper
• First metal put to utilitarian use
• Artifacts dated back to 9500 BC
• Are metals found along with other metals which could be easily worked
• Silver
• Bronze
• Harder than copper, giving it broader applications
• Earliest alloy to be used intentionally
• Bronze replaced Copper because
• Pure copper does not cast well
• No copper ore is pure
• impurities of iron, arsenic, antimony, lead, nickel, and bismuth
• minute quantities of bismuth make copper brittle
• large quantities of lead make copper soft

• The result of a naturally occurring ore
• Used from about 4,000 BC to 3,500 BC
• Fell out of favor
• the smelting process releases arsenic gas which probably killed the metalworkers
• the metalworkers deaths may have been associated with their products
• unpredictable results because the naturally occurring ores have different compositions

• Superior
• copper-tin bronzes are harder and less brittle than copper-arsenic bronzes
• Widely available
• Copper ingots and Tin ingots were available through trade
• Repeatable
• Mixture could be reproduced consistently every time
• Bronze production and trade began to flourish under the Phoenicians
• Phoenicians bronze was 10 % tin and 90% copper
• found throughout Europe and the Mediterranean world
• bought copper in the Mediterranean and tin in Britain

• Copper - Tin alloy
• from 3% tin (mild bronze) to 25% tin (bell metals)
• up to 40% tin for white alloys
• radiantly white alloy
• brittle and hard
• accepts a high polish
• used as mirror or plating

All copper-tin alloys with more than 78% copper are called bronzes. They are chemically very stable. When in dry air the metal does not change at all, while in moist air they produce a beautiful, green, pore-free, surface film (patina) which protects the layers it covers from corrosion.

The tin content makes the alloy hard, bronzes with 6% tin can still be rolled, or hammered, while bronzes with 10-20% tin are usually require casting. Bronzes with more than 20% tin are used for bell casting, these alloys are hard and rather brittle, but when struck they emit a clear note. Even higher tin content (up to 40%) produces radiantly white alloys; like the bell alloys these are brittle and hard, but accept a beautiful polish. They were used for bronze mirrors even in antiquity, and today are called speculum (mirror) alloys.

Bronze was the first alloy intentionally manufactured and used by man. Early bronze was an alloy of copper and arsenic that occur together naturally, and was used from about 4,000 BC until about 3,500 BC. While we do not really know, the copper-arsenic alloys probably fell of favor because:

• 1. they were unpredictable in composition, giving unpredictable properties to the finished product.
• 2. the smelting process releases arsenic gas, probably killing the metalworkers and causing the uses to think the metal was evil.

Bronze was widely used for utilitarian and artistic purposes until iron became cheaper and more plentiful. Bronze continued to have wide utilitarian uses until it became cost prohibitive, now except for a few applications as a bearing metal in the engineering and automobile industries has fallen out of use. Artistically bronze is still widely used in casting sculptures of all sizes, plaques, and bell founding.