The smelter and the smith

 Here is a peek from a new assemblage, a large historical background to science. It is the stuff that did not fit in my Murdoch Book 100 Discoveries, or 100 große Sprünge: Die bedeutendsten Entdeckungen und Erfindungen der Menschheit, (Spektrum Akademischer Verlag).

The idea is to look at the enabling knowledge that opened up science for us.

There were seven metals known in ancient times: gold, mercury, tin, lead, silver, copper, and iron (on rare occasions, it was found as the metal in meteorites). Most of the time, people who wanted to get some metal had to treat an ore in some way, to smelt it to get the metal. Around the same time that coiled pots were showing up around Çatal Höyük, people began to smelt lead, copper and other metals from their ores. The copper might have been from deposits of copper metal (‘native copper’), but lead beads from the same area must have been smelted from lead ore.

A suitable ore had to be available, and then somebody needed to find or know a way to smelt the ore and use the metal. Zinc has probably been smelted in India for at least 2300 years, maybe 3000 years, but the first European zinc was only prepared in 1736 (possibly using technology learned from India, as the method was identical). In the Middle east, where copper ore was available from Cyprus, the early Bronze Age coincided with the start of writing and the development of city states, but bronze was probably in use even earlier, in what is now Thailand.

In some places, like sub-Saharan Africa, there was no Bronze Age at all. People jumped straight from the New Stone Age (Neolithic) direct to the Iron Age, probably because they had iron ore but no copper ore, though perhaps the iron technology was imported. Iron was probably being smelted and worked in the Middle East around 1100 BCE, and it appeared 600 years later in West Africa.

Tin could have been smelted by accident if the right rocks were used to make a fireplace. People say copper and lead might have been discovered the same way, but this is unlikely, because copper smelting needs 1100°C and carbon monoxide to reduce the oxide to metal.

Lead could form by accident if a piece of the ore became buried in the ashes with limited oxygen, but both copper and lead were more likely to form in a potter’s kiln. One attractive theory is that potters began decorating their pots with minerals to add colour, noticed the metals that formed on the pots, and began experimenting.

Charcoal is dry and has 10% of the mass of the wood it came from, so charcoal fires burn hotter, if they have enough (but not too much) oxygen. With good charcoal and the right amount of air, a temperature of 1500°C is possible if the fire is surrounded to keep the heat in. An open fireplace with coals is unlikely to get higher than 600°C, even when a high wind blows through it, because the same high wind that promotes burning also carries away much of the heat. In other words, making metal needed the heat of a kiln or an oven, not the heat of an open fire. It was an art, not luck.

Copper is a soft metal, good enough to make maces but not blades, so Çatal Höyük is generally referred to as a chalcolithic site, a place where copper and stone were both used. Somewhere, somehow, somebody learned to make bronze, an alloy of copper with arsenic or tin. The earliest examples of copper/arsenic bronze come from Asia Minor in about 4200 BCE, while the harder copper/tin bronze was used from about 3200 BCE.

We can come up with plausible yarns to account for people making copper metal, but iron remains a bit of a mystery. It has a strong attraction to oxygen, which is why iron rusts so easily, and why iron oxide is a common iron ore. At around 900°C, the oxygen is more strongly attracted to carbon, so if iron oxide is collected from a bog or some other place, it can be converted to the metal. It takes a great deal more heat to melt iron, but the metal that forms at 900°C can be hammered and worked in a bloomery, and shaped into tools.

Smelting and refining did not always bring blessings. Cores taken from lake beds in the Andes reveal that Peruvians were smelting copper 1000 years ago, but around the year 1450, they switched to silver, which leaves a different pattern of pollution. They probably began smelting more silver because the Incas demanded that taxes be paid in silver. When the conquistadors took over in 1533, the silver-smelting pollution increased tenfold.

The ice of Greenland shows clear traces of pollution from copper production, dating back to about 500 BCE. This probably came mainly from the production of copper and bronze around the Mediterranean, even as they entered the Iron Age. The real advantage of iron was that it was cheap and easy to make iron weapons in large numbers. Even if gentlemen preferred bronze, a thousand poorly-trained peasants with shoddy iron stabbers can overwhelm 300 trained warriors with superb bronze swords.

In the end, a smith needed to shape and toughen the metal.

Shipping may also have been a factor. Ships would certainly have been up to carrying Cypriot copper ore or metal by 2000 BCE, possibly much earlier, but it is tempting to wonder if tin or tin ore was being carried to the Mediterranean from Cornwall by then: tin was certainly being mined and worked in Cornwall in about 2150 BCE. All around, the general picture of early metal working is clear, but many of the finds leave us still wondering. From Weland to Ogoun to Cullann to mpu Gandring, in many cultures (look them up!), the smith is seen as having the powers of a magician—and no wonder...