Long before the so-called “iron age” started, humans knew of iron. There are iron artifacts from the 4th millennium BCE. Humans were fascinated by these small pieces of iron, which were found in meteorites and cherished and valued them. However, usable iron was rare and extremely sought after to the extent that we know it was more valuable than gold or silver. How did humans invent the first technique to produce metallic Iron from ore?

The story of Iron starts with the production of Bronze. Bronze is an alloy of 90% copper. Depending on what constitutes the other 10% we get different types of bronze. The most common type which kick started the bronze age around 3500 BCE in western Asia is tin bronze. Unlike copper ore, tin is hard to find but a small amount of it can significantly improve the quality of copper and make it usable and strong. Ancient smelters produced bronze by melting the natural copper ore mixed with tin ore in simple kilns. The resulting bronze was the primary metal used in tools and arts for more than 2500 years.

Iron is a common impurity in copper ores. We also know that iron ore can, and was, used as a flux in the process of smelting copper. In simple terms, a flux agent is a chemical that attracts oxygen to itself and protects the primary product, which is copper, from oxidizing in high temperatures. Therefore, across the ancient world, bronze smelters had been encountering molten iron when they raised the kiln temperature high enough. However, they discarded the resulting metal because its copper impurity made it too soft and inferior to bronze.

Around 1,200 BCE the collapse of bronze age civilizations in the near east due to a “perfect storm” of drought, famine, disease, immigration and war affected trade routes that brought tin ore to the western Asia. During this time of bronze shortage some smelters seem to have resorted to using the lower quality iron for tool making. They had observed that adding carbon to iron makes it much harder but prone to breaking. We have evidence of iron tools built with layers of soft and hard iron to achieve desired outcomes. Over time iron smelters experimented with different amounts of carbon impurity and achieved desired levels of hardness and strength.

Some high-level observations about the story of Iron are helpful. First, Iron smelting was discovered independently in different parts of the world, but everywhere it was an evolution of the bronze smelting process. Second, the process took several centuries to evolve. The first iron pieces were considered bad bronze and discarded. When tin became rare the producers gradually increased the quality of the bad bronze. In all likelihood for centuries they did not recognize iron as a new metal but rather an improved “bad bronze” . The final notable observation of the story is who these inventors were. They were not the learned people of the ancient world. Rather they were artisans and laborers working in difficult conditions.

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