Modern civilization depends on metallurgical science to produce the proper physical and chemical properties in alloys for a great many purposes. These properties include resistance to corrosion, electrochemical activity, mechanical and structural strength, hardness, density, melting point, elasticity, workability, heat and electrical conductivity, and color (Street and Alexander, 1962). So great are the contributions of metals to mankind that metallurgy must be considered an important factor in the rise of urban civilization (Forbes, 1950) and the foundation upon which the Industrial Revolution and Space Age rest (Aitchison, 1960).
Chemically, a metal is an element which has one, two, or three electrons in its outermost electron shell. Typically, they empty the outmost shell of electrons and become cations (positively-charged ions). The majority of the elements listed in the Periodic Table of the Elements are metals and share the properties of metallic luster, heat and electrical conductivity, malleability, ductility, and sectility.
Alloys are solid solutions of metals that consist of a parent metal with other metals, semi-metals, or nonmetals added that change the physical and/or chemical properties of the parent metal (Street and Alexander, 1962). Every new element added to a metal will affect the mixture's properties producing alloys with strikingly different characteristics from the component metals (Bergose, 1937, Caley, 1973, and Street and Alexander, 1962). Most alloys are produced by mixing metals in the molten state. Metallic native elements such as native copper, gold, silver, meteoric iron, and platinum are not pure metals but are naturally-occurring alloys (Patterson, 1971). Native gold can contain silver, copper, iron, tellurium, bismuth, antimony, mercury, and platinum (Forbes, 1950), and native platinum can contain osmium, palladium, rhodium, niobium, and iridium (Street and Alexander, 1962).
Most of the minerals that contain metals are not in the native state but are naturally-occurring chemical compounds. Smelting is done to separate a metal from a chemical compound (ore mineral). Metals can be won from simple compounds such as oxides by heating in the absence of oxygen (reduction smelting). Metals can be won from complex compounds such as sulfides by heating the ore first in the presence of oxygen (roasting) and then in the absence of oxygen (oxidation-reduction smelting) (Forbes, 1950).
Prehistoric alloys are extremely variable in elemental components and relative percentages. The high percentage of certain components in alloys cannot be accounted for as a result of contamination caused by smelting mixed ores of variable mineral compositions; instead, they are the result of skillful manipulation of alloy compositions to derive desired properties and they were probably the result of experimentation as well (Caley, 1973).
Metallurgy was independently invented in three geographic areas (Coe et al, 1986, Nordenskiold, 1921, and Patterson, 1971): (1) southwest Asia by 7300 B.C., (2) the Lake Superior region of North America by 4200 B.C., and (3) the Andean region of South America by 1500 B.C. Knowledge of metalworking spread from these three metallurgical developmental areas by diffusion into outlying areas where recipient cultures developed regional art styles, metalworking techniques, and mining of local ore deposits (Easby, 1966, Mountjoy, 1969, and Patterson, 1971). The Old World cultural sequences of lithic and metal ages (Paleolithic, Mesolithic, Neolithic, Bronze, and Iron Ages) focused on the concept that developments in stone and metal technology paralleled other social, economic, religious, and material developments and served as a marker for their recognition (Forbes, 1950). Bergose (1937) and Nordenskiold (1921) proposed using the terms Golden, Copper, and Bronze Ages to label the cultural periods of the Andean region as well; however, New World cultural developments did not follow the same course as in the Old World and so the terms were not adopted by New World scholars (Lechtman, 1980, and Patterson, 1971). In the Lake Superior region, hammering-annealing-embossing native-copper technology remained practically unchanged for 5000 years while marked social and economic changes took place (Easby, 1966, and Patterson, 1971). While complex Andean cultures employed full-time craft specialists to produce metal objects employing relatively simple metallurgical methods (hammered-annealed-embossed objects), simpler Andean cultures were engaged in more sophisticated metallurgical methods (lost wax casting and soldering) by part-time craft specialists including the only prehistoric platinum technology using powder metallurgy (sintering) developed in the La Tolita region of Ecuador (Bergsoe, 1937, Meggars, 1966). Another major difference between Old and New World prehistoric metallurgy concerns the metals that were used. The refined metals shared by the prehistoric Old and New Worlds were gold, silver, copper, and tin, but the Old World also utilized iron and mercury (Aitchison, 1960) while the New World used lead and platinum (Lechtman, 1976, and Rivet and Arsandaux, 1946).
The following six-stage developmental series of prehistoric metallurgy synthesizes my own ideas on metallurgical development, with Forbes (1950) Evolution of Metallurgy and Phases of Copper Metallurgy with Pattersons (1971) Stages of Metallurgical Development into a single developmental series:
I. Pre-Metallurgy
A. Earth Pigment Stage - use of metal-bearing minerals
(hematite, limonite, psilomelane, malachite, galena,
orpiment, cinnabar) as paint pigments
B. Metallic Mineral Stage - shaping and polishing of
minerals with metallic luster (hematite, pyrite,
meteoric iron) using stone working methods
II. Incipient Metallurgy
A. Native Metal Stage - recognition that the soft,
malleable native metals (gold, copper, and silver
nuggets and masses) could be shaped by cold-hammering
and cutting
B. Annealing Stage - marked by the discovery that the
effects of strain-hardening due to cold-hammering could
be reversed with the application of heat
III. Metallurgy
A. Smelting-Melting Stage - marked by the winning of metals from their ores by reduction smelting and the mixing of molten metals to produce alloys
B. Oxidation-Reduction Smelting Stage - marked by the
winning of metals from sulfide ores by oxidation-
reduction smelting and the replacement of stone by
bronze for utilitarian tools
The symbolism of metals in prehistoric cultures can be viewed from two different but related perspectives: as a medium of expression and as the material itself. Prehistoric metal smiths were master craftsmen who produced realistic and abstract depictions of a great variety of subjects including people and anthropomorphic beings, animals and composite animals, plants, life scenes, geometric designs, and celestial bodies like the Sun and Moon. Although there are a large number of local and regional artistic and symbolic expressions depicted in metal, these themes are shared through time by many prehistoric cultures. Metal objects manufactured by prehistoric smiths include ornaments, containers and palettes, and regalia.
The value of metal prior to its use as a medium of exchange (general purpose money), and as weapons and utilitarian items, was primarily as symbols of supernatural power and lordly status. At these early times in the history of metal use, gold, silver, copper, and their alloys had little if any market value even though they were important to elites as items of symbolic trade and prestige (Coe et al, 1986, and Reichel-Dolmatoff, 1981). These apparently contradictory set of circumstances concerning the great symbolic value of metals with little commercial value was due to attitudes towards metals. Metals were apparently considered symbols of celestial light and power: gold of the Sun and maleness, silver of the Moon or celestial force, copper of the Moon and femaleness. A mixture of gold (Sun and maleness) and copper (Moon and femaleness) produced an alloy with symbolic properties giving the metal object and its owner power and prestige. Mining, smelting, and smithing were viewed by most prehistoric cultures as male occupations that required fasting, abstention from sex, and prayer to be successfully accomplish. With the replacement of stone by bronze and the use of metals as a medium of exchange, the attitude of people concerning metals also changed to one that remains with us to the present: metal magic changed to metal science.
Aitchison, L., 1960, A History Of Metals, Vol. 2, MacDonald
and Evans Ltd., London, England.
Bergsoe, P., 1937, The Metallurgy and Technology of Gold
and Platinum Among Pre-Columbian Indians, translated by
F.C. Reynolds, Ingeniorvidenskabelige Skrifter, Nr. 44,
Denmarks Naturvidenskabelige Samfund, Copenhagen, Denmark.
Caley, E.R., 1973, Chemical Composition of Ancient Copper
Artifacts of South America, in Applications of Science in
Examination of Works of Art, ed. W.J. Young, Research
Laboratories, Museum of Fine Arts, Boston, Mass.,
P. 53-61.
Coe, M., Snow, D., and Benson, E., 1989, Atlas of Ancient
America, Facts on File, Inc., N.Y.C., N.Y.
Easby, Jr., D.T., 1966, Early Metallurgy in the New World,
Scientific American, Vol. 214, No. 4, p. 72-81.
Forbes, R.J., 1950, Metallurgy in Antiquity, A Notebook for
Archaeologists and Technologists, E.J. Brill and Leiden,
Netherlands.
Lechtman, H.N.
1976, A Metallurgical Site Survey in the Peruvian Andes,
Journal of Field Archaeology, Vol. 3, p. 1-42.
1980, The Central Andes: Metallurgy Without Iron, in The
Comings of the Age of Iron, ed. T.A. Wertime and J.D.
Muhly, Yale University Press, New Haven, Conn.,
p. 267-334.
Meggers, B.J., 1966, Ecuador, Frederick A. Praeger Pub.,
N.Y.C., N.Y.
Mountjoy, J.B., 1969, On the Origin of West Mexican
Metallurgy, Mesoamerican Studies, No. 4, p. 26-42.
Nordenskiold, E., 1921, The Copper and Bronze Age in South
America, Comparative Ethnographic Studies, No. 4,
Elanders Boktryckeri Aktiebolag, Gutenberg, Germany.
Patterson, C.C., 1971, Native Copper, Silver, and Gold
Accessible to Early Metallurgists, American Antiquity,
Journal of the Society for American Archaeology, Vol. 36,
No. 3, p. 286-321.
Reichel-Dolmatoff, G., 1981, Things With Beauty Replete
With Meaning Metals and Crystals in Colombian Indian
Cosmology, in Sweat of the Sun, Tears of the Moon:
Gold and Emerald Treasures of Colombia, ed. D. Seligman,
Terra Magazine Pub., L.A., Calif., p. 17-33.
Rivet, P., and Arsandaux, H., 1946, La Metallurgie en
Amerique Precolombienne, Institut dEthnologie, Paris,
France.
Street, A. and Alexander, W., 1962, Metals in the Service
of Man, Penguin Books Ltd., Harmondsworth, Middlesex,
England.
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