Rio Tinto | Minerals and Metals for the world

The digging detectives
Chris Morrissey journeys back to the cradles of history to discover what's been discovered about the birth of metal industries.

The use of copper and its principal alloys, bronze and brass, encompasses human progress since the Stone Age 60 centuries ago. But through the mists of time who can tell where myth takes over from historical truth? Stories change in the telling, and fragments of fact can become smothered in fanciful embellishments.

For instance, where is the truth in the old story that copper smelting was probably discovered accidentally, when globules of copper were found in the ashes of a wind-whipped campfire? When the story was repeated in a recent issue of Review there were protests that it was implausible.

In fact, physics and chemistry say it is plausible. In the sort of flame you get around incandescent charcoal, common copper carbonates are converted to oxides and the oxides reduced to copper metal. It can be a solid state process, and take place at temperatures that are easily reached in a camp fire. Copper melts at 1,084oC so higher temperatures are needed to separate molten copper from ordinary rock minerals and allow it to flow together into globules. That's where "wind-whipped" comes in, though the heat has to be contained and there has to be some ingredient that promotes fluxing of the rock minerals. Iron oxide does that, so for the early copper smelters it was important to have iron stained ores.

What does the archaeology say? For one thing, it tells us that copper was being used for ornaments as long ago as 7,000BC. That far back, however, the metal was not obtained by smelting of copper minerals but used in the native form in which it is quite commonly found. Deliberate smelting seems to have started a thousand or two years later, probably somewhere in the Middle East or Asia Minor.



The digging detectives Chris Morrissey journeys back to the cradles of history to discover what's been discovered about the birth of metal industries. The use of copper and its principal alloys, bronze and brass, encompasses human progress since the Stone Age 60 centuries ago. But through the mists of time who can tell where myth takes over from historical truth? Stories change in the telling, and fragments of fact can become smothered in fanciful embellishments. For instance, where is the truth in the old story that copper smelting was probably discovered accidentally, when globules of copper were found in the ashes of a wind-whipped campfire? When the story was repeated in a recent issue of Review there were protests that it was implausible. In fact, physics and chemistry say it is plausible. In the sort of flame you get around incandescent charcoal, common copper carbonates are converted to oxides and the oxides reduced to copper metal. It can be a solid state process, and take place at temperatures that are easily reached in a camp fire. Copper melts at 1,084oC so higher temperatures are needed to separate molten copper from ordinary rock minerals and allow it to flow together into globules. That's where "wind-whipped" comes in, though the heat has to be contained and there has to be some ingredient that promotes fluxing of the rock minerals. Iron oxide does that, so for the early copper smelters it was important to have iron stained ores. What does the archaeology say? For one thing, it tells us that copper was being used for ornaments as long ago as 7,000BC. That far back, however, the metal was not obtained by smelting of copper minerals but used in the native form in which it is quite commonly found. Deliberate smelting seems to have started a thousand or two years later, probably somewhere in the Middle East or Asia Minor.
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