Origins of Iron Production
ORIGINS OF IRON PRODUCTION
FOLLOWED BY FEATURE ESSAY ON:
Ironworking . . . . . . . . . . . . . . . . . . 167
Iron is potentially superior to bronze and is much more common than copper and tin, bronze's constituents. Iron's workable ores are widespread in Europe and particularly abundant in the Alpine region. The advantage of iron's abundance was offset because ancient technology could not take full advantage of its properties. Furnace temperatures could not reach iron's relatively high melting point. During the Bronze Age, small bits of iron occasionally must have been produced during copper smelting, but metalworkers could not melt it as they could other metals. When iron ore was intentionally smelted in ancient times, the iron was reduced to metal in the solid state, leaving a spongy mass with slag still trapped in pores. Unlike bronze, which could be cast, iron had to be worked in the solid state to turn it into useful shapes. A smith reheated it in a forge to soften the metal to liquefy any trapped slag and then repeatedly hammered it to force out as much slag as possible while shaping the iron into ingots or finished forms. Reheating and hammering were used in working bronze—they improve the metal. Because iron could not be melted, it could not be enhanced by mixing with other metals, and pure iron does not respond favorably to hammering and reheating, as bronze does. Techniques for dealing consistently with molten iron were not developed in Europe until postmedieval times.
Iron in the solid state takes up carbon and forms a product called steel, but this process requires special smelting conditions that did not occur often in ancient furnaces. There is another chance to introduce carbon into iron during forging, but this socalled case hardening is extremely difficult to achieve. Once steel can be produced on a consistent basis, it does have many advantages over bronze. It is almost as hard as bronze and can be further quench-hardened—reheated and dunked into water. The subsequent extremely hard but brittle steel can be reheated again, and a balance can be achieved between hardness and toughness that is vastly superior to bronze. Steel production is, however, a labor-intensive process requiring specialized skill.
Archaeological evidence for iron production takes four forms: production sites (furnaces and forges), by-products (slag and unused ore), tools, and finished objects. Slag has been excavated at numerous Early Iron Age sites, often in fill, but production areas have been identified definitively at fewer than ten sites. Fortunately, these sites span almost the full time and space of Early Iron Age Europe: the earliest is Tillmitsch in the southeastern
Alps in Austria, dated to 800 b.c., and the latest is Brooklands in southern England, well outside of the Alpine region and dated to 400 b.c. The map shows these two sites and the five more best-known sites that fall between them chronologically, all within the Alpine zone. In general, these sites were hillforts involved in long-distance trade with the Mediterranean world. They bear evidence of other craft production, suggesting that they were regional centers with at least part-time artisans trading finished goods to a hinterland. The raw materials they received in return enabled them to support themselves and also to tap into the long-distance trade.
Smelting and smithing took place at the same locations, and smelting was carried out in simple furnaces where the charge was allowed to cool in place. Forges were of uncomplicated open design not conducive to case hardening. Several dozen slags have been analyzed from some of these sites and from other less well-defined provenances dated to the Early Iron Age. These slags uniformly suggest smelting temperatures of 1,100–1,200°C (2,000–2,200°F), consistent with the type of simple furnace excavated.
Tools—hammers, tongs, and anvils themselves made of iron—are quite rare from Early Iron Age Europe and generally have been found in graves. They, too, reflect a simple technology. On the other hand, by definition, thousands upon thousands of iron objects are known from the Early Iron Age, and by now hundreds of these artifacts have been analyzed. Most of these objects come from graves, a few from settlements, and a handful from the production sites. The earliest iron objects in barbarian Europe are parts of jewelry, sometimes covered with
bronze. Weapons are found a bit later, primarily in graves. Agricultural tools date only to the Late Iron Age.
Analysis has shown that the earliest objects, even the weapons, were almost all made of plain iron. They were not intentionally improved during the forging process, although a few were of steel produced accidentally in the smelting process. The few objects exhibiting case hardening or quench hardening were apparently southern imports. Throughout the Early Iron Age, techniques for improving iron developed slowly, and the most sophisticated techniques do not appear until the end of the Iron Age.
During the transition from the Bronze Age to the Iron Age, the barbarians of temperate Europe were in indirect but steady contact with Mediterranean peoples. Iron production was pioneered in the Alpine region c. 800 b.c., at regional centers that already had advanced methods for working in bronze and were in contact with the south. The Greeks had sophisticated steel metallurgy, and objects of trade entered the barbarian world. The northern bronzesmiths would have recognized iron as an occasional by-product of copper smelting that they had not found particularly useful. The presence of a small amount of Mediterranean iron of superior quality might have spurred barbarian investigations into the new metal, or local conditions brought on by trade and other factors might have led them to experiment with a variety of pyrotechnologies. In any event, there is no evidence that they learned iron production from the south, and sophisticated techniques were developed slowly over a long period of time out of local bronzesmithing traditions. The earliest iron was inferior to bronze and not suitable for many applications, so there was no major technological advantage to adopting it. Iron was at first a decorative material and then came to be used to replace bronze in a few very specific applications, notably in certain types of funerary goods.
Nevertheless, the practice of ironworking spread north and west by a combination of trade and technology transfer. Although in most cases the development continued to be indigenous, in some cases actual migration may have been involved. Ironworking rapidly reached Poland, Germany, and France; it reached northern and western Europe somewhat later. Each local area seems to have developed ironworking according to its own trajectory. Although the use of iron must have had feedback on other aspects of society, it was the other social forces that led to iron production rather than vice versa. The barbarians developed indigenous technology that was to underpin their society from the Late Iron Age until almost modern times.
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Geselowitz, Michael N. "The Role of Iron Production in the Formation of an 'Iron Age Economy' in Central Europe." Research in Economic Anthropology 10 (1988): 225–255.
Raymond, Robert. Out of the Fiery Furnace: The Impact ofMetals on the History of Mankind. Philadelphia: University of Pennsylvania Press, 2000. (Recent general history of metallurgy written for the general public.)
Rostoker, William, and Bennet Bronson. Pre-IndustrialIron: Its Technology and Ethnology. Archaeomaterials Monograph, no. 1. Philadelphia: University of Pennsylvania, 1990. (Survey of prehistoric iron production; much material covers Europe but is somewhat technical.)
Scott, Brian G. Early Irish Ironworking. Belfast: Ulster Museum, 1990.
Tylecote, Ronald F. A History of Metallurgy. 2d ed. London: Institute of Materials, 1992. (General, if somewhat technical, history of metallurgy, including iron and focusing on Europe.)
Wertime, Theodore A., and James D. Muhly. The Coming of the Age of Iron. New Haven, Conn.: Yale University Press, 1980. (Collection of regional syntheses about the origins of iron production worldwide plus background essays on method and theory.)
Michael N. Geselowitz