The Bronze Age
There is evidence that early workers knew that the addition of quantities of tin to copper would result in a much harder substance.
This alloy, bronze, was the first alloy made and found particular favour for cutting implements. Numerous finds have proved the use of both copper and bronze for many purposes before 3000 BC; bronze revolutionised the way man lived.
Some of the earliest bronzes known come from excavations at Sumer, and are of considerable antiquity. At first, the co-smelting of ores of copper and tin would have been either accidental or the outcome of early experimentation to find out what kinds of rock were capable of being smelted. The smelting of lead was known by 3500 BC and lead, tin and arsenic all appear as alloying elements in smelted copper from early dates.
An appreciation of quality in bronze depending on the tin content emerged only slowly. Consistency of composition of bronzes dates back to about 2500 BC at Sumer, with bronzes commonly containing 11-14% tin – reasonable evidence both of technological forethought and the appreciation of metallurgical and founding properties. Indications of bronze production as far back as 2800 BC come from places as far apart as India, Mesopotamia and Egypt, and make a single origin for bronze smelting significantly further back in time a strong possibility.
Trade by land and sea, and the succession of cultures and empires, had dispersed knowledge of the copper-based metals slowly but surely throughout the Old World. By 1500 BC it had spread across Europe and North Africa to the British Isles, and in other directions as far as India and China. Copper, bronze, copper-arsenic, leaded copper, leaded bronze and arsenical tin bronzes were all known by this date in most parts of the Old World.
‘Ötzi’, the 5000 year old mummified man found high in the Alps on the Italian-Austrian border was found with many implements including an excellent arsenical copper axe. The copper axe was hardened by hammering and was much tougher than the stone or flint alternatives. It did not shatter on impact and could be softened by heating and re hardened to maintain its cutting edge. It seems that he was probably a coppersmith himself, since his hair had high concentrations of copper and arsenic, which could probably have come from no other source.
Alloys containing zinc were also emerging at this time, from Cyprus and Palestine, though the alloying is believed to have been natural in origin, due to the local ore containing some smeltable zinc minerals. Alloys similar to modern gunmetals were being cast before 1000 BC though the proportions of copper, tin, zinc and lead were not well established. Following the emergence of true brasses in Egypt in the first century BC, possibly from Palestine, the industrious and methodical Romans rapidly consolidated the knowledge and usage of copper, bronzes, brasses and gunmetals.
Bell founding originated in China before 1000 BC and in time Chinese bell design attained a high degree of technical sophistication. The technology spread eventually through Asia and Europe to Britain, where early evidence of bell making has been dated to around 1000 AD through excavation of a bell casing put at Winchester.
Several important books were written during the Middle Ages concerning the extraction, smelting, casting and forging of copper. These established that the casting and working of copper and its alloys had its origins in craft traditions and practices that had developed over several thousand years. How much of this was originally handed down in writing is not known, since it is only from mediaeval times that the written tradition in technology is unbroken. It is through the Christian monastic and Islamic cultural traditions that detailed accounts of these early technologies have survived. The writings of the monk Theophilus in the 11th century, and of Georgius Agricola and Johannes Mathesius in the 16th century, all describe in detail the metal producing technologies of their day. Often these had changed little for centuries.
The output from the Bronze Age mines was considerable – an assessment based on old mine maps and studies of prehistoric workings at Mitterberg in the Austrian Alps indicated that about 20,000 tons of black copper had been produced there over the period of the Bronze Age. Black copper was the usual product of ancient smelting and contained about 90% copper. It was traded as flat cakes weighing a few kilograms for later refining to purer copper by ‘poling’.
Significant engineering uses had been found for copper as early as 2750 BC, when it was being used at Abusir in Egypt for piping water. Copper and bronze were employed for the making of mirrors by most of the Mediterranean civilisations of the Bronze Age period. The obliteration of Carthage by the Romans has obscured developments in Northern Africa at that time. Evidence of the considerable engineering skills of the Carthaginians has emerged, including the earliest known use of gear wheels, cast in bronze.
Bronze was used in many of the artefacts of every day Roman life – cutlery, needles, jewellery, containers, ornaments, coinage, knives, razors, tools, musical instruments and weapons of war. This pattern of use tended to be repeated wherever the smelting of bronze and copper was introduced, though necessarily on different time scales. The New World and Africa lagged in these developments by 3000-3500 years because of the distance and isolation of these areas from the trade routes that loosely bound the ancient world.