Folks: a few related questions:

How many of you use tool wrap for heat treating? I imagine this is just for those who heat with a controlled furnace, since you can't see through the wrap to judge the blade's temp.

What's the advantage of wrapping a blade in stainless steel foil? (I'm guessing that even heavy gauge aluminum foil would burn up at typical heat treating temps, correct?)

Thanks for any guidance here.

HT foil is heavy gauge stainless steel, not aluminum. I use it for heat treating air hardening steels (currently A2 and 13C26 if I ever finish another one). Since I have it handy, I also use it for spheroidal annealing and recently used it for normalizing three blades. Works great if you're careful with the folds and expressing excess air. Loves to take blood sacrifices -- gloves are your friend.

Overmodulated, I think the true advantage is that when you seal your part in the foil it is heated in the absence of oxygen therefore no scale is formed. If you are a tool and die person and have machined a part to close tolerances you only want to have to remove a little stock to get your finished dimensions on a surface grinder. I have seen people put newspaper inside the foil and because of the lack of oxygen it did not burn until the foil was opened to drop the part in the oil.

all sounds good - tx. but for those using coal or gas forge who can't see through the SS foil warp, they'd be hard pressed to know when the steel is ready for quenching, right?

If you're heat treating by eye in a forge then neither SS wrap nor air hardening steels are very useful.

dlpierson has a valid point, but could you maybe place a simmilar sized piece of steel alongside it and watch the heat on that ?

I think the problem is this: steels that are suitable for heat treating by eye are all water or oil hardening, and you'd have to remove the SS wrap before quenching in order to get a proper, reliably uniform quench. Generally if you stop to fiddle around with that sort of thing between the forge and the quench, the piece will have cooled too much. As far as I know, SS foil is normally used for air hardening steels, which don't present the same problems. You could use it to prevent decarb during annealing; in that case slow cooling isn't a problem.

I've seen it on several of the knifemaker's supply sites. Anyone tried it or something like it? PCB There's also a higher temp verson of this stuff, but I think this might be just the ticket for most of the "normal" steels we use Ie. 1095, O1, 5160, etc.? Any input here? Also looks to be a fair bit cheaper than the foil depending on how much you end up using per blade.

I recently used a painted-on solution of alcohol and boric acid (roach killer) as an anti-scale compound during heat treating, and I was extremely pleased with the results. (Obviously, you let it dry first. The alcohol evaporates quickly, so this isn't a problem.) I did not invent this idea. More discussion here: http://www.iforgeiron.com/forum/f90/heat-treating-my-homemade-anvil-14523/index3.html#post135362