Naturally occurring metals tend to be heterogeneous, which means that various elements can be found in the material. These impurities that occur in natural metals can be separated from the material by melting the metal at its melting point. By heating the material to its melting point, the unwanted material will separate from the desired metal and will also make the material malleable. Malleablility is how easily a material's shape can be changed by applying pressure, usually through hammering.
Annealing is the process of heating and reheating metals to a high temperature to reduce the stresses that occurred in the material. When metal is heated and then allowed to cool, it becomes more malleable and easier to manipulate it into a desired shape. After the impurities in desired material have been removed through the use of heat the material can be heated to a point where it becomes molten. The molten copper can be poured into precut molds to make tools such as axes, plows, jewelry, and other desired objects.
Smelting, the process of separating
metal from other impurities present in it, began possibly around
4,000 B.C. in Africa. [1] By smelting material
its strength and malleability is greatly increased. To separate metals
from other materials, the material has to be heated to a high
temperature and could only be exposed to so much oxygen during this
process otherwise the desired material would not be produced.
Smelting requires a high degree of knowledge. The technique of smelting was not just a chance discovery made by early humans. Removing the impurities from copper, while giving the material enough oxygen, and heating the material to a high temperature required careful planning and a great deal of skill. Smelting cannot be done over an open campfire it had to be done in an enclosed fire, a potter’s kiln. A kiln is an enclosed furnace used to heat clay until it hardens and can be used in the smelting of metal. The kiln is used for smelting in order to keep as much oxygen out as possible and to heat the copper to a high temperature to melt the metal.
The smelting of lead and copper led to the discovery of iron. The Iron Age began in 2000 BC in Asia Minor. Iron working began in Iran sometime around 1500-1000 BC and slowly spread to the rest of the Mediterranean. The period between the 4,000 B.C. and 2,000 B.C. is known as the Chalcolithic Period. During the Chalcolithic period humans experimented with metallurgy, mostly working with gold, copper, and tin. But the first evidence of humans manipulating metals predates the Chalcolitihic era. At sites in Iran and Turkey, there has been evidence found that humans were experimenting with metallurgy as far back as 8,000 B.C.[2]
Written by Alex Boyce, 2003