Excerpt

The Steely Grip of the Ancient Blacksmiths

This past weekend I was collecting experimental data on the relationship of how good you feel to the number of hobbies you have. Specifically, I was trying to harden a small steel pin that was needed in a metal working project. The process was simple enough. I heated a piece of tool steel with a torch until it was cherry red and stopped being attracted to a magnet. Then I stood back and cautiously dropped it in a can of oil. Presto! Very hard steel. During this process, I felt a connection with my ancestors. (Maybe it was just the hair on the back of my hand that I singed.)

Working with iron is one of the oldest skills known to mankind. Only chipping stone and working with copper and bronze (copper-tin alloy) is older. The first iron was heated and hammered (forged) into the shape of spear points and other tools about 4000 BC in ancient Egypt and Samaria, using stones as hammers. This was well before the process of extracting iron ore from rocks (smelting) was developed, so the source of the iron was the occasional iron-nickel meteorite that these early folks found. The guy with the iron-pointed spear fashioned from a flaming meteor from the sky probably had rock star notoriety.

Beginning in 3000 BC, smelted iron began to appear in small objects. These objects are distinguished from meteoric iron by the lack of nickel that is always present in metallic meteors. The smelted iron objects were still mostly ceremonial because the metal was much more valuable than gold.

At widely different times in different parts of the world, the so-called Iron Age took hold. Copper and bronze were gradually replaced with iron. At first, the iron was mostly a low-carbon form. The spongy iron obtained by smelting iron ore was repeatedly hammered and folded to remove impurities (slag) left from the rock. The process also tended to remove most of the carbon. We would call this wrought iron today. The material was useful but would not maintain a sharp edge for weapons and tools. First in the Middle East and later in other parts of the world, blacksmiths discovered that iron heated for long periods with charcoal and quenched rapidly in water or oil was hardened. Although not understood at the time, this process produced an alloy of iron and carbon, which we would call steel, on the surface of the piece. Steel could be sharpened to a fine, persistent edge.

Over centuries, blacksmiths learned, by trial and error, how to control the hardness of the steel layer that could be formed on an iron piece. The sword makers, like the famous Japanese Samurai sword makers, became experts. Hardness is key to creating a keen edge, but very hard steel is so brittle that it will actually shatter like glass. At the other end of the hardness scale, steel is somewhat soft but quite tough. If steel is heated to an intermediate temperature lower than the cherry red critical temperature and cooled suddenly, the hardness can be adjusted to a range of intermediate levels. This very tricky process is called tempering. A Samurai sword has a hard edge, tempered to prevent chipping, and a softer body for toughness.

Today, metallurgists tell us that rapid quenching of carbon steel traps a particular, microcrystalline structure called martensite that gives hardness. Tempering dissolves some of that structure. Steel is now mostly worked in factories by machines. The few remaining blacksmiths mostly create artistic objects. Still, a piece of glowing metal seems to take me back a few thousand years.