8. The Neolithic Expansion

8.6 Metallurgy

The importance of materials in the advance of civilization is apparent in the naming of epochs, from the Stone Age through the Bronze Age and Iron ages. The recent European industrialization period may be called a steel period and nowadays we have the ongoing silicon age and petroleum age. Since prehistory, people have put newly discovered materials to practical use long before they understood much about them.

Man’s intentional use of metals is apparent as early as 9,000 years ago. Native copper hammered into the shape of tools was found at Cayonu Tepesi in Eastern Turkey, located near a deposit of native copper, copper ores and malachite. The hot working of copper and lead, i.e. smelting, casting, forging and alloying was practiced at Catal Hüyük, also located in Anatolia. Cultures such as the Papuan, Micronesian and Polynesian depended on stone tools because they never had ores at their disposition. Polynesians stole whatever piece of iron or copper they were able to put their hands on, when boarding the first caravels and galleons that entered their waters.

The hunger displayed for metals by higher civilizations and the influence metals had on further developments are immense. The development of the ability to smelt metals from their ores was an important force for the change from an essentially agricultural society of the late Neolithic period, to the society based on craft specialization and hierarchy that began 3,500 years ago with the Bronze Age. Bronze weapons were the technological advance by which Barbars were subjugated. Tin and copper ores were actively sought after. The Phoenicians ran expeditions as far as Cornwall to obtain tin ores. Steel, for its part, was an invention of the Hittites who kept it secret. It gave the Hittite Confederation, military dominance over the Egyptians.

It can be argued that the recognition that certain metals are attractive and rare, such as silver and gold, also had a social impact. The emergence of concepts of wealth, power and hierarchy, associated with the possession of gold and silver, did as much to change the nature of early societies as the widespread utilization of the copper alloys did. After the invention of money, silver and gold became important, and the Phoenicians exploited the silver mines of Spain. Hannibal, who was in the personal possession of such mines, was able to mount a military expedition against Rome, which almost annihilated that rising power. It was with the silver extracted from the mines of Attic, at Mount Laurion, that the Athenians paid for the ships that destroyed the Persian invasion fleet, at Salamine. The gold mines of Thracia allowed Philip of Macedonia to flood Greece with enough gold to ruin it, and his son, Alexander, bought it21.

The Romans were so metal-hungry that the boundaries of the Empire (against any strategic and political wisdom) went as far into barbarian lands as was needed to control the mines known at that time. Caesar conquered Egypt for its wealth. The Spanish monarchy granted three caravels to Columbus, despite their need on the battlefront against Islam. In part, this was because of the promise of a huge return in terms of gold: Islam had suppressed the inflow of gold into Europe from Africa and gold was badly needed. The American gold gave Spain the possibility of buying cannons in the Low Countries and building the Great Armada, which was planned to conquer Great Britain.

8.6.1 Gold, silver and lead

Gold was used for ornamental purposes prior to any human record22. This metal is available in large quantities as its metallic form, is easily recognizable and is so malleable that it can be worked cold with no particular ingenuity. If pure alluvial gold was available, almost all societies used it. The earliest description of the concentration and crushing of gold ores appears in Egypt. Inscriptions on monuments erected by the 4th dynasty about 6,000 years ago describe gold washing. According to Agatharcides, who wrote 2,200 years ago, the ancient crushing appliances were hand mortars and millstones of a type used to grind flour.

Silver, contrary to gold, is by no means sufficiently abundant in its native state to account for all the silver used by the Ancients. Native silver is not as rare as native lead but it is still only two-tenths of a percent as abundant as native copper. Silver is usually present in nature in an oxidized state among lead ores such as galena, and must be reduced. The Ancients reduced silver with lead. Lead must therefore have been known contemporaneously with silver, or prior to it.

Metallic lead melts at 327 °C. Whereas there is no way to smelt copper minerals on a campfire because the temperature reached is not high enough, the commonest ore of lead (galena) is so easily smelted that it would be possible to extract lead from it on a campfire surrounded by a ring of stones. Lead smelting began at least as early as the ninth millennium BP. Lead was known by the civilization of Catal Hüyük, a city founded in Turkey about 9,000 years ago.

The separation of silver and lead by cupellation may have been known since 5,000 BP, or before. The lead-silver alloy is smelted in a crucible and held at a temperature of about 1,100°C, as air is blown over it. The air oxidizes the lead, transforming it into lead monoxide. The silver is not oxidized and remains in the crucible as a molten globule. The discovery that silver could be obtained by cupelling silver-rich lead must have stimulated an increased interest in the smelting of lead.

The appearance of quantities of silver artifacts in the fourth millennium predates the evidence for the start of copper melting. An increase in the smelting of one group of ores could be expected to lead to an increase in the efficiency of smelting practices in general. The oldest examples of smelted copper are from the early fourth millennium, at Tepe Yahya, in Iran, i.e. at least 3,000 years after the smelting of lead.

8.6.2 Bronze

8.6.2.1 Copper

Like gold, copper has been in use since prehistoric times. Native copper was available to primitive people and could be hammered into shape. It is easily recognizable as being different from earth. In the same way, malachite and other copper ores usually have a distinct color, sometimes vivid green. These ores were used very early in time to paste on the eyelids, not for esthetic purposes but in order to keep away flies, which caused terrible and catastrophic ophtalmies. Copper and copper ores were sought for other reasons than metallurgical ones.

The quantities used were such that very early in time, native copper must have been replaced by ores. The copper found in pits in Europe, prepared during the Bronze Age, contains a small amount of sulfur that indicates that this copper originated from oxidized ores, presumably copper sulfate. These ores had to be reduced into metallic copper during the process of smelting. Copper objects are scattered all over Asia Minor and found as early as 3,000 BC. The metal is mentioned in Chinese records (the Shoo King), but even less is known of Chinese metallurgy than of Egyptian. The remains of Mycenaean, Babylonian, Phoenician and Assyrian civilizations have yielded endless objects of copper and bronze. The copper of this pre-Roman World, ending about 500 BC, seems to have originated largely from the Sinai and, later, from Cyprus.

The Romans carried extensive copper mining, from Egypt through Cyprus, Central Europe, Italy, Spain and Great Britain. The metallurgy of copper is an extraordinary technological advance. Yet, copper is such a weak metal that the superiority of copper tools is not immediately apparent. This is perhaps why the extremely conservative Egyptians did not adopt it for a long time. Bronze tools made of copper plus tin are by far superior to pure copper. The bronze objects found in Cyprus show the presence of 2% to 10% tin, although tin is not known to exist on the island.

8.6.2.2 Tin

Tin is a relatively rare metal of interest early in metallurgy because its alloy with copper would render that metal harder, in the form of bronze.

It has been claimed that the first bronzes were obtained through the smelting of stanniferous copper. This may be true for Western Europe. In the Near East and India, it does not seem that such a stanniferous copper might be found. Also, lumps of tin found in Cornwall in conjunction with copper and mixed with bronze celts (Neolithic axes) under conditions indicating the Bronze Age, are evidence that, even in Europe, independent smelting of the two metals was the custom.

The origin of the supplies available before the Phoenicians came on the stage is unknown. It may have been alluvial or else originated from India, Malacca or Africa. At about 1,100 BC the Phoenicians began the importation of tin from Spain and Britain.

8.6.2.3 Bronze

Copper and tin melt around 1,100°C. It is sufficient to plunge the ores into a pit containing charcoal, burn it and, with time, the metals will melt and flow reasonably pure at the bottom. The production of bronze requires three different metallurgical processes when copper and tin are smelted and purified separately. This would make it more difficult than the preparation of wrought iron.

The superiority of copper and bronze objects over stone and especially obsidian, was by no means evident and took a long time to be realized. The first reason was the rarity of the metal object versus stone that was available in relatively large amounts and the second was that the stone axe could be sharpened at will. Its only real flaw is that it is irremediably lost when broken whereas copper tools could be resmelted and reused. This was of course of paramount interest for civilizations developing in a barren mineral environment. Tools and weapons made of native copper had no great advantage over those made of flint or obsidian. The initial delay of a millennium between the first appearance of copper objects and the metallurgical revolution of the Early Bronze Age can probably be ascribed to the delay in the development of the ability to make arsenical or tin bronze alloys, with their superior metallurgical properties. Arsenical bronze was almost certainly discovered accidentally, when copper ores that contained arsenical impurities were smelted. The natural bronze so produced would soon have been found to be much harder than native copper. The intentional production of arsenical bronze may have quickly followed.

Once the superiority of bronze was assessed, a great amount of prospecting and trade took place since, in general, copper and tin ores lie far apart.

8.6.3 Iron

The belief that an Iron Age succeeds a Bronze Age is mainly based on the negative fact that, for various civilizations, no iron tools were found for a long time after many bronze and copper objects were available. The conclusion drawn that iron objects are absent because they were not made by primitive civilizations can be disputed because iron objects are readily oxidized and prone to disparition, which is not so much the case for bronze or copper.

An iron object has been found as early as 3,700 BC in Egypt, in the pyramid of Kephren. Another piece dates back to the 6th dynasty (3,200 BC). Wrought iron does not need a high temperature to be made and is in reach of any evolved sapiens sapiens culture, as the hill tribes of Northern Nigeria demonstrate. They reduce iron from hematite in village forges. A pasty mass is produced by heating and subsequently hammered to make it exude the slag. The hammered mass is the bloom, from which wrought iron is prepared. There is no doubt that such a technique can give satisfactorily refined objects only after a good mastering of the process. Since bronze is more difficult to prepare, one may suppose that wrought iron was also known.

However, wrought iron is no steel. In fact, iron metallurgy is much more difficult to master than that of bronze. Most iron ores, even if by far more abundant than copper or tin, are hardly discernible from earth and would thus not be sought after. The only easily recognizable iron ore is pyrite, which contains sulfur. The smelting of this ore will produce iron that will always contain some sulfur. Such a contaminated iron is extremely unsatisfactory. Indeed, contrary to copper and tin, iron has disturbing solvative properties: some substances may dissolve in it and the contamination may lessen the valuable metallurgical properties of the metal.

The production of liquid iron requires a temperature that is considerably higher than that needed for wrought iron. Pure iron melts at a considerably higher temperature than copper: about 1,525°C. Iron, like all other metals, was originally melted with the heat provided by a charcoal fire. During the heating, the charcoal would literally dissolve into the iron, which can absorb up to 4.2 % carbon. This phenomenon will lower the melting point of iron to a readily accessible temperature of about 1,150°C but the carbon-containing iron is brittle and fragile. It breaks easily and was valueless to the Ancients for weapons and ploughs. After the iron has melted, it can be cast and left to harden again. This indirect method to gain malleable iron originated only around 1550 AD. Cast iron was systematically made only at the end of the 14th century for the making of cannons.

Through a process of decarburisation that entails the expulsion of the carbon within the iron ore to less than 2.6% by combining it with oxygen, purer and harder iron is obtained, called steel. During the decarburisation process, the melting point of the iron climbs up again to about 1,500 °C and this high temperature is not easily reached.

In addition, the iron exists under different crystallographic forms at different temperatures and under different treatments. These differences bestow the iron with different ductile properties, sometimes by dissolving the residual carbon within the crystal frame. Very hard steel is obtained when a minimal amount of carbon, i.e. 0.4%, is present in an iron that has been abruptly cooled down, for example with immersion of the red-hot metal in cold water.

Iron has been in use all over Europe since 3500 BC. The smelting was done in shallow pits with charcoal. Egyptians soon devised small furnaces with forced draft. Bellows appeared around 1500 BC and steel was produced 500 years later. The first description of the making of tempered steel is in the Odyssey:

And as armourers temper in the fjord
The keen-edg’d pole-axe, or the shining sword,
The red-hot metal hisses in the lake”.

Translated by Pope.

Homer wrote around the year 900 BC. The Odyssey of Ulysses is supposed to have taken place 300 years earlier, after the siege of Troy by the Achaeans in 1194 BC. Homer may have been historically wrong by assuming that the Achaeans knew tempered steel. The Odyssey was written considerably later than the Iliad. In the Iliad, Homer mentions also iron but only as a metal with which ploughs are made. For warfare purposes, the Achaeans used bronze like their forefathers the Mycenaeans.

Greece was overrun in 1100 BC by Celtic Dorians who knew how to prepare steel and expelled the Achaeans. The Hittite Confederation in Anatolia also used the metal for warfare purposes, around 1300 BC. The autodestruction of the Confederation by civil war in 1160 BC favored the use of iron in a more general way. The Celts of Austria prepared reasonably pure steel around 500 BC. Cesar won the battle of Alesia (52 BC) against the 250,000 men of Vercingetorix with only 40,000 legionaries not only because of discipline but also because their largely superior armament. The Merovingian Franks irremediably beat the Romans, and the Vikings in the 6th century, because they had devised a steel blade of hybrid structure made of a tough core supporting a hard cutting edge.

In the East, the primitive method of India and Japan for making steel was to seal wrought iron with charcoal and sawdust in crucibles, and heat the whole preparation over a long period of time. The Indian steel was furnished to the Romans without them knowing its origins or secrets of fabrication. After the Arab conquest of the Near East and North Africa, the Indian steel was transported to Damascus and Toledo. The Arabs thereafter also produced the same steel.

References

21. Except Sparta, that declared itself not for sale.

22. Metallurgical processes developed by the Ancients have been described by the Saxon Georgios Agricola: “de re metallica” written in 1552 and translated by H.C. Hoover and L.H. Hoover in 1950 (Dover publications, Inc. New York 14, NY.

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