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No. 399:
Early Metal

Today, we see metal fired in the arts. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

The stone age drew to a close around 3500 BC as we took up metals. We began the new age by picking up the odd gold nugget, the stray lump of meteoric iron, and the glittering piece of alluvial silver. We began by hammering ornaments from those natural metals.

Natural deposits of metal are sparse. Yet the malleability of metal opened huge possibilities for artisans. It didn't take long to find we could expand the supply of metals by smelting ores. We smelted the first copper by accident when potters made glassy glazes from copper-based pigments.

For smelting, we needed both ore and forests of wood for fuel. Both were plentiful in the northern part of present-day Iran and in Russia above it. So we began serious copper smelting outside the ancient cradles of civilization.

But smelting meant hotter fires than any we'd ever made. Fire had also been brought under control by the late stone age pottery industries. Now we had to add forced draft to the old pottery kilns. We had to stoke fires hot enough to liquefy gold and copper -- hot enough to refine them into pure components.

You see, surface gold is usually an alloy. It has silver mixed in it. Egyptian artisans first used each natural alloy of gold and silver as a different material. They used the different colors of gold alloys to create exquisite objects of art.

Most copper ores are also impure. They're usually mixed with natural tin. We made the hard, copper-tin alloy that we call bronze accidentally, before we learned how to control composition. Only in Egypt, where copper ore was fairly pure, did a copper age give way to a bronze age. That happened when Egyptian craftsmen started alloying their copper to make it stronger.

It was 1500 BC before we could finally refine the natural alloys into elements. We finally mined tin separately and purposely alloyed it with copper to make the best bronze.

Iron melts at 3000° F. It was 1200 BC before we figured out how to reach temperatures like that. When we did, iron became the metal of choice in the Western Mediterranean world.

1200 BC was also when the Old Testament books began to take shape, and you can read our new fascination with metal in them. Those books are shot through with gold, silver, iron, copper, lead and bronze. The new metals touched our imaginations. By 1000 BC metal ingots, called talents, were the new medium of exchange in the Mediterranean basin. Up to now each stage in the use of metal had been driven by the arts. Now metal was poised to return the favor and to reshape civilization itself.

I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.

(Theme music)

Singer, C., Holmyard, E.J., and Hall, A.R., A History of Technology. Vol. I, New York: Oxford University Press, 1954, Chapter 21.

This episode of The Engines of Our Ingenuity was aired in 1990. Since then we've learned more about early metal use. See e.g., Episodes 1877 and 640.