These were my raw materials: a rusty, blunt old file G gave me, and the broken and slightly wormy handle of a hammer I found at the tip.
I ground the teeth off the file, then forged it to roughly the shape I wanted:
Then annealed it to make it easier to work:
After quite a lot of filing and grinding, it looked like this:
I fired the forge up again to harden it, then tempered it in the high-tech thermostatically controlled electric furnace (while wibble_puppy heated a tin of beans on the top):
I cut off a non-wormy piece of the hammer handle, drilled a small deep pilot hole in it, and burnt the tang in (heating just the tang with a blowtorch while the blade was in a tin of water to keep it cool so that it didn't lose its temper). I'm not sure what type of wood the handle is made from - maybe hickory? It's very hard indeed.
After a few hours of whittling, sanding, oiling, polishing and sharpening, I ended up with a very nice wood carving knife:
Here it is alongside my other, commercially-made knives for comparison.
From the top there's my knife, a Mora Erik Frost 106, a Mora 120, a Ray Iles whittling knife, and a Flexcut KN13(?) detail carving knife.
I haven't used it yet other than whittling a point onto a bit of scrap dowel to try it out, but I think it's going to be pretty nice to use. The blade is quite thin (thinner than I originally intended - I had to grind quite a lot off to get it completely flat and smooth) and very sharp and pointy, so I suspect it will be better suited to fine work on green or soft wood than heavy roughing-out and hard stuff. For a first attempt I'm quite pleased with how it turned out.