Forge Welding Iron — Joining Two Pieces into One

Forge welding is the oldest method of joining metals — predating riveting, brazing, and soldering. Two pieces of iron are heated to bright yellow-white heat (around 1,300 °C), then hammered together on the anvil. At this temperature the iron surfaces bond permanently at the atomic level, creating a joint that is as strong as the parent metal.

This single technique made possible every complex iron object of the pre-industrial world: chain links, gate hinges, plough shares, barrel hoops, and swords. Without forge welding, a blacksmith can only make objects from a single piece of iron. With it, the smith can build up any shape from simple stock by joining, scarfing, and folding.

The critical challenge is preventing oxide scale from forming on the surfaces during heating. A flux — traditionally clean sand or borax — is sprinkled on the joint surfaces. The flux melts at a lower temperature than the iron's welding heat, dissolving the oxide and floating it away as liquid slag when the hammer blows land.