Metallurgy deals with the study of metals and their ores as well as the processes for extracting, purifying, and alloying metals and production of metal objects. Humans have practiced the use of metals in various forms for nearly 9,000 years, beginning with copper during the eighth millennium BC. Cross-culturally, the processes involved with working metals are often shrouded with superstition and magical beliefs. Although the production of some metals requires sophisticated technology, there is virtually no culture in the world today that does not use at least some metal objects.
Common metals employed throughout the world include copper, silver, gold, lead, iron, tin, zinc, and arsenic. Of these, the first three occur in relatively pure or “native” form, whereas the others occur only in chemical compounds from which they must be extracted before use. Common metallic compounds from which metals are extracted include metallic salts, phosphates, and carbonates. Although some of these compounds exist in surface deposits, most metals and metal ores are mined.
The earliest documented uses of metals occurred in Iran and Anatolia during the eighth millennium BC in the Old World and circa 1500 BC in the Andes Mountains of the New World. In both cases, the first metals used were relatively pure forms of copper mined with stone and antler tools and processed with simple cold hammering techniques.
Later metal workers developed uses for alloys, that is, mixtures of a metal with one or more additional elements, often metals. Alloys are often favored because they offer technical properties that are not present in constituent elements. Common alloys include bronze (copper and either tin or arsenic), brass (copper and zinc), and pewter (tin, copper, antimony, and sometimes lead). Steel, one of the hardest metals, is made from alloying iron with carbon and sometimes other components such as manganese, chromium, and nickel.
The so-called “precious metals”—gold, silver, and platinum—are relatively rare and therefore expensive. Gold and silver especially have a long history of use as jewelry and other ornaments. Although they are obtainable in pure forms, they are often used as alloys to reduce the cost of objects and to create desirable characteristics of hardness and color.
Mines are usually used to extract metal ores from the earth if veins of ore are not available on the surface. However, native gold, called “placer gold,” occurs in alluvial deposits and can be collected by panning or washing. In most cultures, mining is considered a relatively undesirable job, even where the potential economic benefits are lucrative. This is due in part to the perceived, and often real, danger of underground mining. In addition to the apparent threats from explosives, heavy equipment, and possible cave-ins of mine shafts, miners face unseen dangers in the form of noxious gasses and airborne compounds, such as silica, that can damage the lungs.
Many cultures also maintain beliefs about supernatural beings that can influence the lives of miners. One such being is the Tio of Andean mines. Tio takes the form of a devil, often red with pointed horns, and inhabits a shrine located within the mine tunnels. Andean miners make offerings of cigarettes, coca leaves, and alcohol to propitiate Tio, who is asked to reciprocate in the form of pure ores of high value.
Traditionally, mining has been carried out by men, but women and children often participate by working mine tailings and panning. When mine work is part of compulsory service, families often accompany male miners to provide food, clothing, and other needs for the miners. Children are sometimes preferred workers in mines because their smaller size makes it easy for them to move around in small mine tunnels and their small fingers are thought to be agile at separating ore from other rocks and debris. In most countries, the use of children’s labor in metal extraction is officially discouraged, but small subcontractors often continue to employ their illegal labor.
Smelting involves heating metal ore to a high temperature to remove unwanted material from the ore. To achieve this, the ore must be melted in a ceramic crucible. At high enough temperatures normally achievable only in a closed furnace, the waste material (or gangue) will melt out and be left behind as slag. The long hours involved in smelting and the enormous requirements for fuel and air circulation, often by the use of bellows, mean that smelting is usually a group activity. Men are most often directly involved with smelting, but women and children may help to provide fuel to heat the furnace. Perhaps because the purification process happens out of sight, in the heat of the furnace, it has often been associated with ritual and magic. For example, worship of the Yoruba Orisha Ogun, the deity of iron, is closely associated with male smelting activities.
Whether as native metal or as alloy, metals may be worked and formed into objects in a variety of ways. Soft metals, such as copper and gold, may be hammered cold, representing the earliest metal working techniques. Smithing uses the heat of a forge or hearth to make metals more pliable so that they can be worked into shape with a hammer and anvil. Blacksmithing, the working of iron and steel, is accompanied by both skill and ritual knowledge that can require long apprenticeships to obtain. This is the case with Japanese master sword makers, who use elaborate techniques of folding, annealing, and tempering to produce blades that are strong, flexible, and beautiful. Casting involves the heating of metal to a liquid state and pouring it into a mold. Bronze, one of the first metals to be cast, was so widely spread in the Old World that the periods characterized by its appearance are referred to as the Bronze Age. Metals may also be cut or ground to produce desired shapes.
The use of metals in pure or alloyed form varies among cultures and depends in part on available technology and intended uses. Common uses for metals include tools, weapons, personal adornment, coinage, art, and symbols of state (e.g., medals, crowns, scepters).
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