Whenever you see a photo of a blacksmith you usually see “sparks” flying out in all directions. This doesn’t happen in most forge work. It only really happens when you fire weld.
Fire welding. It’s one of the best things in the world.
In this photo I’m welding a piece of mild steel folded over around a piece of recycled car coil spring to make a knife. It’s been in the fire long enough that the surface of all the layers is molten. It’s gone beyond white hot, the surface is liquid steel under a layer of molten metal oxide. My task is to judge this heat just right (too cold: no weld, too hot: it burns away) and hit it together with just the right amount of force before it cools down too much. This pushes out the molten oxide (like too much jam in a sandwich when you squeeze the bread together). That’s what makes the lightshow. The molten metal surfaces should then fuse together as one continuous piece.
The finished knife is one of these.