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No. 385:
African Steel Making

Today, ancient African ingenuity gives us steel. 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.

Modern steel-making began in 1847. William Kelly of Eddyville, Kentucky, found he could make superior structural iron if he blew air through molten pig iron. Oxygen from the air burned harmful elements out of the iron and formed a very strong carbon steel. The process gave what we call converter steel. Nine years later the Englishman Henry Bessemer reinvented Kelly's method. Today we talk about the Bessemer process for making carbon steel.

But carbon steel had been made long before either Kelly or Bessemer. One of the oldest and most sophisticated methods was that of the Haya people. They're an African tribe in what is Tanzania today. The Hayas produced high-grade carbon steel for about 2000 years.

The Hayas made their steel in a kiln shaped like a truncated upside-down cone about five feet high. They made both the cone and the bed below it from the clay of termite mounds. Termite clay makes a fine refractory material. The Hayas filled the bed of the kiln with charred swamp reeds. They packed a mixture of charcoal and iron ore above the charred reeds. Before they loaded iron ore into the kiln, they roasted it to raise its carbon content.

The key to the Haya iron process was a high operating temperature. Eight men, seated around the base of the kiln, pumped air in with hand bellows. The air flowed through the fire in clay conduits. Then the heated air blasted into the charcoal fire itself. The result was a far hotter process than anything known in Europe before modern times.

Anthropologist Peter Schmidt wanted to see a working kiln, but he had a problem. Cheap European steel products reached Africa early in this century and put the Hayas out of business. When they could no longer compete, they'd quit making steel.

Schmidt asked the old men of the tribe to recreate the high tech of their childhood. They agreed, but it took five tries to put all the details of the complex old process back together. What came out of the fifth try was a fine, tough steel. It was the same steel that'd served the subsaharan peoples for two millinea before it was almost forgotten.

This ancient African steel was the fruit of unalloyed human ingenuity. This complex metal, flowing from simple native elements, forms a mute tribute to the power of the human mind over matter.

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

(Theme music)

Shore, D., Steel-Making in Ancient Africa. Blacks in Science, Ancient and Modern (I. Van Sertima, ed.) New Brunswick: Transaction Books, 1983, pp.157-162.

As a footnote to this episode, which I did around 1990, I subsequently learned more about William Kelly's role in inventing the Bessemer process. It was less than I'd realized at the time. See Episode 762 for Kelly's story.