Bronze Working

Metalworking Background

Perhaps one of the most important technological advances of the ancient world was the breakthrough in metalwork. Metalworking was invented at various places and times in the ancient world, and also varies from culture to culture in technique. Compared to bone and stone implements, metals allowed people to make much better tools such as hoes and needles. Stronger weapons such as axe heads and daggers for protection could now be made. Metals were also used as currency and for decorative purposes. Because of the time and resources needed, an armband or well-crafted pendant made from bronze could show power and prestige. Oftentimes chieftains or high ranking officials would wear such items.

The Importance of Copper

To understand the importance of bronze and how it was manufactured, we must first take a look at copper. Bronze is any copper alloy, but it is typically alloyed with tin. As it is very malleable in pure form, copper is generally accepted as the first metal to be used by ancient peoples. Worked copper artifacts appear around 3500 BC; however, some artifacts have been dated as early as 7000 BC. Copper is a fairly easy metal to work-- it could be annealed (cold worked with a hammer) or melted and then poured into moulds. While copper tools and weapons had definite advantages over stone, copper does not have a very good cutting edge. Because it is so easily worked it has a tendency (daggers and short swords especially) to bend easily.

For reasons not fully understood (possibly by accident?), arsenic was added to copper. As an alloy (any combination of at least two metals), arsenic gave copper the cutting edge it lacked. Armed with new knowledge of mixing metals to make alloys, many metal smiths began experimenting with other metals. Metal smiths used tin, a soft and mineable metal, in similar ways as copper. Tin, when mixed with copper, made bronze. Compared to copper and arsenic-copper alloys, bronze is much stronger.

Tin Bronze

Tin bronze is typically made in two ways, but both require high temperatures. Scraps of metal could be melted in crucibles (vessels which are heated from the outside) using hot charcoal. It is also possible to obtain sufficiently high temperatures by forcing air through a grate in the furnace bellows. After the furnace is hot enough , the crucible is placed in the center through a small door in the side of the furnace. After the metals were liquefied, the crucible would be removed and the contents quickly poured into a mold where the metal would be allowed to cool.

The first way to create tin bronze is to mix casserite, a tin oxide, with copper. The metals are heated to 950 degrees Celsius, the melting point of bronze. The casserite is reduced to tin and absorbed by the copper. There is little evidence that the second method was utilized widely. Smelted and pure tin is added to molten copper to create bronze. After the new bronze item cooled, it could be further worked with a hammer and then polished to a high luster.

Edited by Emily Hildebrant
February 25, 2008