THE SIGNIFICANCE OF BRONZE

Bronze is an alloy, a crystalline mixture of copper and tin. The ratio is set ideally at 9:1, though it varied in prehistory as a result of either manufacturing conditions or the deliberate choice of the metalworker. Bronze can be cast or hammered into complex shapes, including sheets, but cold hammering has an additional effect: it elongates the crystals and causes work hardening. Through work hardening, effective edges can be produced on blades, but the process can be exaggerated, leading to brittleness and cracking. Heating, or annealing, causes recrystallization and eliminates the distortion of the crystals, canceling the work hardening but enabling an artifact to be hammered into the desired shape. Moreover, the presence of tin improves the fluidity of the molten metal, making it easier to cast and permitting the use of complex mold shapes.

Because of the long history of research on the topic of European prehistory, the sequence of metallurgical development is well known. Newer work, particularly in the southern Levant, has shed fresh light on the context of metallurgy in a milieu of developing social complexity. Bronze production on a significant scale first appeared in about 2400 b.c. in the Early Bronze Age central European Únětice culture, distributed around the Erzgebirge, or "Ore mountains," on the present-day border between Germany and the Czech Republic. It is no accident that these mountains have significant tin reserves, which many archaeologists believe probably were exploited in antiquity, although this point is the subject of controversy. Farther west, tin bronze was introduced rapidly to Britain from about 2150 b.c., so that there was no real Copper Age. Here, the earliest good evidence for tin production is provided by tin slag from a burial at Caerloggas, near Saint Austell in Cornwall, dated to 1800 b.c. Significantly, Cornwall is a major tin source.

ARSENICAL COPPER: THE FIRST STEP

An issue that divides many modern scholars is the extent to which ancient metalworkers were aware of the processes taking place as they smelted, refined, melted, and cast: Were the metalwork and its compositions achieved by accident or by design? This controversy is an aspect of the modernist versus primitivist debate, which pits those who see the people of prehistory as very much like ourselves, practicing empirical experimentation, against those who doubt the complexity of former societies and their depth of knowledge.

This is particularly the case with respect to arsenical copper, an alloy containing between 2 percent and 6 percent arsenic, which was used in the Copper Age of Europe during the fourth and third millennium b.c. It. continued to be produced and to circulate for some time after the introduction of tin bronze. Like bronze, arsenical copper is superior in its properties to unalloyed copper. The arsenic acts as a deoxidant. It makes the copper more fluid and thus improves the quality of the casting. Experimental work has shown that cold working of the alloy leads to work hardening. Thus, while arsenical coppers in the as-cast or annealed state can have a hardness of about 70 HV (Vickers hardness), this hardness can be work hardened to 150 HV. In prehistoric practice hardness rarely exceeded 100 HV, however; this hardness compares favorably to that of copper, which also can be work hardened. It has been claimed, however, that many of the artifacts in arsenical copper were produced accidentally and that their properties were not as advantageous, as is sometimes claimed. This is argued not least because of the tendency of arsenic to segregate during casting (to form an arsenic-rich phase within the matrix of the alloy and, in particular, close to the surface of the artifact).

Some copper ores are rich in arsenic, such as the metallic gray tennantite or enargite, and it is argued that arsenical copper was first produced accidentally using such ores; the prehistoric metalworkers then would have noticed that the metal produced was mechanically superior to normal copper. Furthermore, arsenic-rich ores could have been recognized from the garlic smell they emit when heated or struck. Arsenic, however, is prone to oxidation, producing a fume of arsenious oxide; this fume is toxic and would deplete the arsenic content of the molten metal unless reducing conditions (i.e., an oxygen-poor environment) were maintained at all times. The "white arsenic smoke" and white residue produced during melting and hot working probably would have been noticed by metalworkers as correlating with certain properties of the material. This loss probably explains the greatly varying arsenic content of Copper Age arsenical copper.

Whether or not arsenical copper was produced deliberately, it has been noted that daggers were made preferentially of arsenical copper in numerous early copper-using cultural groups of the circum-Alpine area, such as Altheim, Pfyn, Cortaillod, Mondsee, and Remedello. Similar patterns have been noticed in Wales, and in the Copper Age southern Levant there was differentiation between utilitarian metalwork in copper and prestige/cultic artifacts in arsenical copper. Although arsenical copper produces harder edges than does copper, this deliberate choice of raw material may have been based on color rather than mechanical properties. As a result of segregation, arsenic-rich liquid may exude at the surface ("sweating") during the casting of an artifact in arsenical copper, resulting in a silvery coating.

THE COMING OF TIN

Cassiterite, tin oxide ore, is present in various areas of Europe in placer deposits. These are secondary deposits that are produced by the erosion of orebearing rock, and the cassiterite is then redeposited in alluvial sands and gravels. The high-density, hard, dark pebbles of "stream tin" presumably would have been known to prehistoric people searching for gold. Stannite, a sulfide of tin, sometimes occurs in ore bodies in association with chalcopyrite and pyrite, and the weathered part of such deposits would contain cassiterite.

Tin, however, is very rare. Although some placer deposits probably would been worked out and are therefore not known today, tin's distribution is very uneven in Europe. Indeed, it is perhaps no accident that its earliest regular use appeared in the Únĕtice culture, around the tin-rich Erzgebirge. It has been suggested that the rich "Wessex" graves of the early second millennium in south-central England owe their wealth to their control of the rich Cornish tin of the southwest peninsular. The gold Rillaton cup, from Cornwall, tends to support such a hypothesis as it documents the accumulation of wealth presumably amassed through the tin trade. Other major sources occur in western Iberia and Brittany, although there is no hard evidence for their working in the Bronze Age. In Anatolia Early Bronze Age mining is known at Kestel and tin processing nearby at Göltepe, in the Taurus Mountains of southern Turkey.

It is thought that the complex societies of the Aegean and eastern Mediterranean obtained their tin from Turkey, Afghanistan, or the eastern desert of Egypt. The presence of tin ingots in the Ulu Burun shipwreck, which sank about 1300 b.c. near Kaş off the southern coast of Turkey, shows that metallic tin was circulating in the Late Bronze Age Mediterranean. Tin smelting is relatively inefficient (the slags at Caerloggas contain 45 percent tin oxide), but it can be added easily to copper by putting cassiterite and a flux (to facilitate the chemical reaction) on the surface of molten copper under charcoal. Bronze Age metallic tin (which is, in fact, unstable) is found rarely, which supports the hypothesis that the direct addition of tinstone (cassiterite) to molten copper was preferred. This process also guarantees a consistent alloy, whereas arsenical copper production could not be controlled so easily.

As noted, bronze presents distinct mechanical advantages over copper. The presence of tin improves the fluidity of the molten metal, making it better suited for casting, and lowers its melting point: 10 percent tin will lower the melting point of bronze by some 200 degrees. Bronze in its as-cast state has a hardness of about 100 HV, which can be improved to about 170 HV by cold working. It is probably no accident that the widespread use of stone arrowheads and daggers declines only with the change from arsenical copper to bronze in the Early Bronze Age (as, for example, in northern Italy). This is partly because bronze becomes more widely available as a result of increased production but also as metal edge tools increase in effectiveness.

LEAD ADDITIVES

During the Late Bronze Age lead was used as an additive to bronze. Lead certainly improves casting, lowering the melting point of the alloy and improving its viscosity, but the main reason for its use may have been to bulk out copper in a period of metal shortage. Breton socketed axes often have high lead contents, and in Slovenia it is noticeable that different artifact types contained varying amounts of lead, axes having 6–7 percent and sickles 3–4 percent. Deliberately added lead appears in British bronze in the Wilburton phase (1140–1020 b.c.), continuing in the succeeding Ewart Park (1020–800 b.c.) and Llyn Fawr (800 b.c. onward) phases.

COPPER PROCUREMENT

Copper is more common in Europe than is tin, and it is likely that prehistoric miners worked outcrops that are of no economic significance today. Bronze Age mines are known at Ross Island (2400–2000 b.c.) and Mount Gabriel (1700–1500 b.c.) in southwest Ireland, and workings at Alderley Edge in England date to the first half of the second millennium b.c. There are extensive contemporary underground workings at Great Orme's Head, Llandudno, on the north coast of Wales, and mining also is documented at Cwmystwyth and Nantyreira in the west of the country and at Parys Mountain on the island of Anglesey.

In Spain mining is documented at Chinflon in the south and at El Aramo and El Milagro in the north, while in southern France it is known at Cabrières and Saint-Véran–les Clausis. There is Copper Age mining in Liguria, in northwestern Italy, at Libiola and Monte Loreto, and the ores around Rudna Glava, near Bor in Serbia were exploited from a very early date (fifth millennium b.c.). There are also fifth millennium dates for the mines at Ai Bunar, and Bronze Age working is indicated at Tymnjanka in Bulgaria. There is some evidence for Copper and Bronze Age mining at Špania Dolina and Slovinky in central Slovakia. None of these mines, however, seems to be on the same scale as Bronze Age workings in Austria and Russia. The Mitterberg mines are situated in the Salzach valley, near Salzburg in Austria; here, there are Bronze Age adits up to 100 meters long, and it has been calculated that as much as 18,000 tons of copper were produced in prehistory. At Kargaly, southwest of the Urals in European Russia, it seems that mining was conducted on a massive scale, with an estimated 1.5–2 million tons of ore produced.

METALS ANALYSIS AND PROVENANCE

A large body of metals analysis exists for prehistoric Europe; the Stuttgart program of spectrographic analysis, for example, effected some 22,000 analyses. Many of the sampled artifacts date to the Copper and Early Bronze Age, as it was thought that compositional analysis would be particularly useful in shedding light on the emergence of metallurgy in Europe. Statistical analyses of these data have thrown up metal composition groups, although these are contested. There are numerous methodological problems. Prehistoric artifacts do not have homogeneous compositions, not least because of segregation of elements in cast artifacts. Unfortunately, some of the elements determined by these analyses show this characteristic, such as arsenic, whose segregation we have already discussed. Furthermore, ore bodies vary in composition through the outcrop, so that provenance is difficult to ascertain. Recycling seems to have been practiced from the Early Bronze Age (because one of the advantages that metal presents over stone tools is that broken artifacts can be repaired easily and the raw material reused), which means that metals from different sources may have been melted together. Finally, the effect of alloying on the composition of impurities in metal is not understood completely.

Sometimes compositional groups correspond with artifact types. The Early Bronze Age ingot rings (Ösenhalsringe or Ösenringe), very commonly found to the north of the eastern Alps in southern Bavaria, lower Austria, and Moravia, represent one example. They frequently are made from a metal that is conventionally referred to as "C2," or "Ösenring metal," and which probably is linked to Austrian copper sources. Peter Northover has used data on impurity groups and alloy types to argue convincingly about metal circulation zones in Britain and northwestern Europe. He also was able to suggest sources for the supply—for example, the earliest metal used in Britain seems to have come from Ireland, and, in the Late Bronze Age, metal from central European sources was used.

METAL AND SOCIETY

It is a commonplace of prehistory that the development of the metals industry is linked to the growth of social complexity. It is, however, worth noting that it was the Australian prehistorian Vere Gordon Childe, in his The Dawn of European Civilization, who saw the "qualities . . . which distinguish the Western world" as beginning in the Bronze Age. It is, however, debatable whether the metals trade caused the emergence of elites or whether, conversely, their emergence favored the development of metallurgy.

Metal is a medium for producing efficient tools and weapons that could be repaired without the loss of material, but it also is uniquely suitable as a mark of status. It was scarce, particularly in the earlier phases of its use, and this rarity was compounded by the use of tin, which was even scarcer than copper. Metalworkers with the requisite skills to perform the "magical" transformation of green copper ore into metal may have been equally scarce. Metal would have caught the light in a way that no other substance in use at the time did; bronze, in particular, could be formed, by casting or working, into complex shapes to make ornaments, tools, and weapons but also sheet metal. The latter material could be used in the production of armor—helmets, grieves, and shields—and vessels. Sheet armor, which is arguably less efficient than leather or wood, would have had a definite display function, as would bronze vessels, not least because of the expertise required for their manufacture. The Greek epic poet Homer, author of the Iliad and the Odyssey, who wrote in the first half of the first millennium b.c., gives us a picture of the heroic warriors at the siege of Troy. His Late Bronze Age Aegean warriors bear impressive bronze sheet armor, helmets, and shields, which are regularly described as "shining" or "flashing,"

The use and possession of metal therefore can be seen as a measure of wealth, and this is particularly true for an area such as Denmark, which was entirely dependent on outside sources for its copper and tin. Such attempts to ascribe value to prehistoric commodities are risky, because we can only speculate on the relative scarcities of raw materials or the cost of labor input and guess at the ritual significance or the biographies of artifacts. For example, in much epic literature weapons acquire value by virtue of their previous owner, like Achilles' spear in Homer's Iliad.

Because copper and tin are distributed unevenly, the desire for raw materials bound together European society in a metals trade. We are not sure which organic commodities were traded for metal, but control of resources and craft specialists seems to have acquired increasing importance. Thus, Late Bronze Age fortified settlements of the Urnfield period appear to have acted as regional metallurgical centers, and some smaller settlements seem to have had no production of their own. The importation of Continental scrap metal into Late Bronze Age Britain is evidenced by the cargo of the Middle Bronze Age Langdon Bay ship, wrecked off Dover in the English Channel. Mining gave upland communities, naturally poor in agricultural resources, such as the Late Bronze Age Luco/Laugen groups of Trentino–Alto Adige in the Italian Alps, a commodity to tie them in to wider economic and status networks.

the social position of bronzeworkers

A key concept in understanding the growth of social complexity is that of craft specialization, where individuals are dedicated to specific economic tasks rather than participating in domestic food production. As copper metallurgy developed, many crafts emerged, including prospecting, mining and ore dressing, smelting, and refining, casting, and finishing. It is likely that at least some of these crafts were protected, secret knowledge. Gordon Childe (in The Bronze Age) suggests that bronzesmiths were an itinerant caste, outside the social structures of society, who traveled from settlement to settlement to ply their trade. Increasing documentation for metalworking within settlements, as at the Italian lake villages of Ledro and Fiavé, coupled with the lack of support for this model in the ethnographic literature, has led archaeologists to argue for permanent workshops: community-based and possibly part-time production. Thus, Michael Rowlands has suggested locally based seasonal production. Metal types can have surprisingly wide distributions, and the transmission of models or ideas (rather than itinerant smiths) is documented, for example, by the early Urnfield flange-hilted swords, which show close similarities from the east Mediterranean to western Europe.

Excavations by Stephen Shennan at an Early Bronze Age mining village in the Salzach valley, Sankt Veit–Klinglberg, indicate that the metal smelters were already craft specialists, importing foodstuffs and using ores won from various outcrops. In the Late Bronze Age the massive concentrations of smelting slag found, for example, on the Lavarone-Vezzena plateau in the Trentino Alps, in southern Italy, or on Cyprus suggest large-scale industrial production, although it is significant that both are tied in to the Mediterranean markets of the period.

metals make the world go round

It is not clear to what extent bronze and the metals trade in general were responsible for the growth of social complexity in Bronze Age Europe. Was bronze a relatively minor component in complex patterns of wealth display involving many perishable elements (such as livestock, furs, and textiles), which do not survive in the archaeological record? Is the significance of bronze that it provided the catalyst for the development of complexity, as has been claimed for the southern Levant, or was the emergence of the elites of barbarian Europe an independent phenomenon? It seems that social stratification already had begun to develop in Neolithic Europe, and copper and then bronze gave the emergent elites a useful and rare raw material whose control enabled them to consolidate their power as well as a perfect vehicle for display. The "beauty" of the Bronze Age warrior was very much bound up in his armor, his shining bronze.

See alsoOrigins and Growth of European Prehistory (vol. 1, part 1); Early Copper Mines at Rudna Glava and Ai Bunar (vol. 1, part 4).

bibliography

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Mark Pearce