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Precious Metals: Bronze Jewelry



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Bronze Jewellery

Source: Man Made - Anatolia (Turkey), Cyprus, Egypt, Iran


Bronze is typically a mix of copper and tin, and may contain small amounts of lead or arsenic. The ratio of tin to copper is typically between 5 percent to 15 percent. Bronze is a somewhat generic term that refers to a broad range of copper alloys. Although both copper and tin naturally occur, the two ores are rarely found together.



Bronze develops a patina, but does not oxidize like pure copper. Although the term "bronze" was originally applied to any copper alloy that contained tin, the term is now used generically to describe a variety of copper alloys, including aluminum bronze, manganese bronze, or silicon bronze.


Ming Dynasty Bronze MetalWorkers

Ming Dynasty bronze metal workers (c.1637)

   Cassiterite Tin Oxide

Cassiterite (tin-oxide)


The tin used in bronze alloy is a byproduct of the mineral cassiterite (above, right) which is a tin-oxide mineral that contains around 5 percent tin, making tin a relatively rare commodity. Cassiterite is found in alluvial or placer deposits.


The Bronze Age

The "Bronze Age" refers to a period in the development a civilization when metalworking advanced to the point where techniques were created for the smelting of copper and tin or arsenic from naturally occurring ores. The first "bronze" metal alloy of copper and arsenic was developed as early as 4200 BC in Asia Minor (Anatolia), and copper/tin alloys were developed by the ancient Sumerians as early as 3500 BC (Early Bronze Age c.3500-2000 BC) in the Tigris-Euphrates Valley of modern day Iraq. The inhabitants of the Indus Valley also began their Bronze Age around 3300 BC.


Bronze Age Castings

Bronze Age casting & ingots

   Igbo bronze vessel

Igbo bronze vessel (photo: public domain)


With the discovery of bronze, warfare dramatically changed. With the addition of arsenic and tin, the hardness of copper was dramatically increased, and the weaponry it produced was no match for the stone maces of the period. Bronze was also made into body armor which was impervious to weapon strikes.

Bronze made an appearance in China around 2000 BC. Early Chinese bronze castings were made by pouring the fusible liquid metal into sand, clay or stone molds. During this period, bronze was used to make art objects, coins, jewelry, and tools. Bronze was also used extensively in ancient Egypt, and foundries were used to create large decorative castings used in architectural details. Bronze was also popular for making weapons as it was harder than iron, and highly resistant to corrosion.


Orichalcum

Orichalcum is the golden-colored bronze alloy used in ancient Roman coinage (sestertius) which may have contained varying amounts of gold, copper, tin and/or zinc. The orichalcum alloy was also used in dupondius (brass) coins from the Roman Republic./P>

In the ancient world, orichalcum was considered more valuable than copper, and some anthropologists believe that it could have been used as a substitute for gold in jewelry. Orichalcum is similar to the Andean (Incan) alloy known by the Spaniards as tumbaga. Orichalcum was first mentioned by Hesiod in the 7th century BC, and in the Homeric hymn dedicated to Aphrodite.



Bronze can be a harder metal which has a hardness of between 5.5 to 6.0 on the Moh's scale, and a Vickers Hardness (VHN or HV) of between 60 (fully annealed) and 258 (cold worked). Bronze has a melting point of 1030 C.


Chemical composition: (Cu), (Sn)





Books on Jewelry Making
Books on Jewelry Making


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