The Bronze and Iron Ages
The Bronze Age is a period in a civilization's development when the most advanced metalworking (at least in systematic and widespread use) consisted of techniques for smelting copper and tin from naturally occurring outcroppings of ore, and then alloying those metals in order to cast bronze.
Rome explored all around the Mediterranean for mineral wealth to support its growing empire. The Romans also acquired immense Phoenecian mineral wealth when they destroyed the Phoenician colony of Carthage. This wealth included the great metal mines of Spain. A huge copper deposit was found in the southwest corner of Spain. Copper and iron on the surface of the Earth at that deposit coloured a nearby river red. It is thus called Rio Tinto. The deposit originally consisted of a reddish mountain, with iron, silver and gold as well as copper.
1200 to 1000 BC in the Near East is considered the transition from Bronze Age to Iron Age. Paradoxically, it is not the smelting of iron that distinguishes the Bronze Age from the Iron Age. At least one Mesopotamian smelted iron artifact (distinguished from meteoric iron by its lack of nickel) dates from 5000 BC. Increasing numbers of smelted iron objects appear in Mesopotamia, Anatolia, and Egypt between 3000 and 2000 BC, including a circa 2800 BC iron sword from Tell Asmar. But iron in the Early Bronze Age was rare and expensive. At the end of the third millennium, iron appears to have been five times as expensive as gold. The weapons and tools made of iron are ceremonial in nature, and the other uses of iron are ornamental.
From 2000 to 1600 BC references to iron appear in literature with some frequency but it remained a ceremonial or ornamental metal. At least one Old Assyrian text records that iron was eight times more valuable than gold. Only in the late Bronze Age from 1600 to 1200 BC does iron start to become a working metal in some regions and even then bronze remains the dominant metal for weapons and tools. Many scholars believe that early iron production was not intentional, but a by-product of smelting other metals. Forbes points out that the Nubian gold gravels from which Egyptians obtained gold dust were rich in magnetite sand. While not as dense as gold, magnetite is considerably denser than other common sand minerals, and is often found with gold. Forbes believes that when the Egyptians melted gold, at least some magnetite ended up in the crucible producing small quantities of iron between the gold and the slag. One objection to this theory is that iron is 50% soluble in gold at gold’s melting point, and therefore little iron would be present separate from the gold itself. However panning for magnetite is far easier than panning for gold so this theory has at least a surface plausibility.
An older theory postulates that ancient smelters may have mistakenly used iron ore instead of copper ore in the production of copper or bronze. The smelter having discovered that wrought iron was inferior to bronze because it would not hold an edge saw no reason to intentionally smelt iron. One very serious problem with this explanation is that iron remained more valuable than gold throughout the Bronze Age. Iron ores were relatively abundant. The quantity of iron produced by such a smelting mistake, and the absence of the desired metal would have suggested the ore was the source. It seems unlikely that a smelter would not repeat such a mistake if the result was a metal as valuable as iron. In the 1960s, another theory of iron as copper smelting accident came out of experimental archaeology.
Based on archaeological evidence as well as traditional Near Eastern smelting practices, Wertime and Smith demonstrated that the iron ores sometimes used as flux for copper smelting can be reduced to sponge iron as part of the copper smelting process. This model explains why the Bronze Age produced iron but only in very small quantities. Smelters used a variety of materials as fluxes. Depending on the temperature, the amount of oxygen present, the iron content (if any) of a particular flux, and the quantity of flux used, the production of sponge iron would have seemed a completely random event. Thus the smelter would be unable to reliably repeat the process that had accidentally produced iron.
Waldbaum suggests the beginning of the Iron Age was “when iron ceased to be considered precious and was finally accepted as the predominant material for making tools and weapons.” A more quantifiable definition distinguishes three stages of iron development. In the first stage a society uses iron for ornamental purposes, or for ceremonial tools and weapons not for working use. In the second stage the society uses iron for utilitarian purposes, but bronze still predominates. In the third stage the society uses iron more commonly than bronze as a working metal. This definition is somewhat more useful because it distinguishes the first stage (which is still in the Bronze Age) from the second and third stages. This determination can be made by examining the number of iron and bronze implements archaeologists find associated with each period and culture. But this still doesn’t explain why iron replaced bronze. Iron is not superior to bronze for tools. Wrought iron the form first encountered by Near Eastern smelters is roughly equivalent in hardness to annealed 10% tin bronze, and inferior to all cold-worked tin bronzes. It is only when carbon dissolves into the iron (carburization) and the artisan quenches the resulting steel that ferrous metals have a definite hardness advantage over bronze.
The development of steel of course made iron production essential. Indeed 1200 BC is a commonly accepted date not only for the start of the Iron Age, but also for the discovery of carburization of iron. While the location of this discovery remains uncertain, it appears that in the Hittite kingdom a blacksmith discovered how to make steel by heating iron in contact with carbon. But the production of steel was probably quite random at first. Throughout the eastern Mediterranean area in the first two centuries of the Iron Age, iron weapons appear alongside bronze weapons, with no evidence that iron provided any military advantage over bronze weapons. The discovery of carburization was apparently an accident and the discoverer probably did not know how he did it the first time. Until the eighteenth century AD the conversion of iron to steel was misunderstood as removing some impurity from iron not adding carbon to it. Ferrous artifacts become more common after 1200 BC, but they do not replace bronze immediately. In fact ferrous metals replace bronze first in tools, then in weaponry. The discovery of carburization was almost certainly an accident as was quenching of steel, since neither is a component of bronze working.
The Iron Age thus roughly corresponds to the stage at which iron production was the most sophisticated form of metalworking. Iron's hardness, high melting point and the abundance of iron ore sources made iron more desirable and cheaper than bronze and contributed greatly to its adoption as the most commonly used metal. By 1200 BC, iron was widely used in the Middle East but did not supplant the dominant use of bronze for some time.
Classically the Iron Age is taken to begin with the Greek Dark Ages in the 12th century BC in Greece and the Ancient Near East, the 11th century BC in India and between the 8th (Central Europe) and 6th (Northern Europe) centuries BC in Europe. The Iron Age is usually taken to end with the onset of historical tradition during Hellenism and the Roman Empire or the Early Middle Ages in the case of Northern Europe.