Forge welding
Forge welding is a welding process of heating two or more pieces of wrought iron or steel until their surfaces are malleable and then hammering them together.
Often a flux is used to keep the welding surfaces from oxidizing and producing a poor quality weld. A simple flux can be made from borax, sometimes with the addition of iron filings.
Care must be taken to avoid "burning" the metal, which is overheating to the point that it gives off sparks from rapid oxidation.
Multiple layers of different kinds of iron and steel can be forge welded together to produce pattern welded or Damascus steel. A similar process is used to produce the blades of katana.
