Well, tempering can be loads of fun.....
Here is Froglips Official Take on All He Might Think About This:
Basic steps are to heat the tool up to a orange/read heat, then quickly quench in oil or water. This hardens the metal. Aka, you get all the atoms really jumping around then freeze them in place. When you quench, be sure to swirl the tool around. Otherwise an air gap exists between the tool and the quench bath negating the desired effect.
Best cheap heating luck I've had is with two mapp gas torches. An Oxy-Acetylene rig would be even better. You can hold the tool over the heat, or if you have some fire bricks, make a little mini-oven.
Now you "should" have metal so hard a file won't cut it.
Then you want to temper the metal to a compromise hardness. Something you can sharpen but won't fold or crumble when you look at it sideways
The idea is to heat the tool so it brings out a straw or yellow color. This is a surface oxidation. If you kept going, the yellow would turn blue and you'd have a soft tool.
I'd suggest indirect heating. Place the tool on a flat piece of cast iron, aka skillet. Then heat the skillet. Its a bit slower, but I find it a more controlled technique. I'd also suggest laying the chisel so the face is up. You want to see that side turn yellow. If its flat face down on the heat, by the time you see straw on the top, its probably too late.
If you want to free hand it, a tip is start back from the edge, maybe 1 or 2 inches, so the heat runs up the chisel to the end. Of course, don't heat the nice wood handle
Then on to heat treating, which is tough to do with a handled tool, so I'd say skip it. If you want to, the idea is to subject the metal to a low head for an extended period of time to releave stresses.
There are tons of good books out there on heat treating your own tools. I happen to have/like Tool Making for Woodworkers by Ray Larsen, Make your Own Woodworking tools Mike Burton, and an classic The Recycling, Use & Repair of Tools Alexander Weygers.
Any "real" tool makers or metal worker should and probably would scoff at this approach. You can't control temps or oxygen like they can. But, I think the results are good enough to save what is otherwise a good doorstop or rocking table leg wedge.
Jim
