Wrought iron heated in contact with charcoal (carbon) at high temperature produces carburized iron or steel, which is more malleable than cast iron. Steel can be hardened by quenching (practiced as early as the tenth century B.C.E.), that is, cooling off the red-hot steel by sudden immersion into a vat of cold liquid. As a result of the quenching process, the iron object becomes hard and brittle; the hard component is known as martensite (after German metallurgist Adolf Martens). The brittleness is reduced by tempering or reheating. Annealing is the process of softening and rendering less brittle a metal hardened by hammering. Heating at low temperature prevents cracking while hammering.

At Har Adir in Upper Galilee, a remarkably well-preserved “steel pick” with an oak handle within the socket was found in an eleventh-century b.c.e. fortress. It was made of carburized iron (steel) that had been quenched and then tempered. This extraordinary artifact, one of the earliest known examples of steel tools, is a tribute to the skill (or luck) of the artisans of ancient Palestine. Ta‘anach’s iron artifacts, dating from the tenth century, include both tools (sickles, plowtips, blades) and weapons (arrowheads, armor scales). Muhly notes the parallel between this inventory and a familiar biblical passage: “All Israel would go down to the Philistines to repair any of their plowtips, mattocks, axes, or sickles” (1 Sam. 13:20).

Muhly explains the shift from copper to iron as a response to the shortage of bronze, a crisis caused by the disruption of international trade routes. Stager explains the shift from bronze (alloy of copper and tin) to iron in terms of ecological change, particularly deforestation. “Iron production is much more fuel-efficient than copper smelting and processing. Copper requires two to four times as much wood charcoal as iron.”