Ancient steel

AVI sent me a link about an iron chisel (900BC) from Rocha do Vigio (Portugal), which possibly was effectively tempered steel.

The paper has more details about the chisel (they were able to do studies on the haft, but because they are destructive, not on the tip) and their attempts to reproduce the stelae that seem to date from that era also: plus or minus a couple of centuries (some say 1300-800BC, others 1000-600BC). The rocks were of an extremely hard varieties of quartzite and quartz-sandstone. They tried stone chisels, which worked about as well as you'd expect. They tried replica iron chisels made using the processes they knew were in use--some hardened by heating and quenching, and one left unhardened. The unhardened one didn't do much of anything. The hardened ones did, though they had to be resharpened every 5 minutes, and re-hardened after a while too. And:

Specimens in four representative binary alloys with 10, 12, 14 and 16% tin have been cast by Bastian Asmus, ... The unambiguous result on the quartz-sandstone was that none of the bronzes could penetrate the surface

I'll get back to that in a moment. It does sound like the sculptors needed something better than one of the out-of-the-box iron chisels of the area.

The iron chisel they found was in spectacularly good shape--when they did a section of it the bulk of the artifact was uncorroded. They could determine the chemical makeup of different regions of the chisel. It looked rather as though an inhomogenous bloom was hammered into a blob that was made into a chisel. Some sections were high carbon, others not so much. Maybe they paid better attention to the tip, but if the haft makeup is any guide it seems as though they weren't being systematic with the iron makeup.

I suspect that a lot of technological progress now and in the past has come about when men were "just playing around." You can come up with a just-so story or three for discovering what can happen (if the iron happens to be the right makeup) when you quench red-hot iron. And if the overseer is curious about why some rods got tougher and others didn't, he might come up with some rough-and-ready tests for what "good" iron tips should look/taste like. Then everything depends on how secret he wants to be about it. "Gorri made really good iron, but his apprentice's stuff is mediocre."

Usually I put in a phrase like "what jumped out at me was", but several things did this time--mostly to my admiration. I liked that they tried to cut stone with stone; covering all the bases. But they said their bronze chisels "have been cast by". Bronze was hammer worked for maximum hardness, and the result is supposed to be about as hard as unhardened medium steel. One variety of bronze can be hardened to 95 HRb, which is comparable to some low end steels. I wonder if the test was quite fair--if the bronze was merely cast and not hardened.

And, btw, high carbon steel rusts faster than iron does. We're less likely to find steel artifacts, and might draw the wrong conclusions from the absence.

For the curious, Neil Burridge offered one of his bronze swords for destructive testing. It doesn't hold up to modern steel swords, but other experiments say it would have been a match for old iron swords.