Once the blade was shaped right I did some sanding & buffing to make it nice. Then comes the fun part - hardening.



Basically the process is to heat the metal up to Very Hot, when it stops being magnetic due to a change in the crystal structure. Then you quench it cold very quickly by plunging it into some oil. It is now VERY hard, BUT very brittle. So you have to soften it a litte, a controlled softening, using an oven (there are other ways to do this but I thought the oven would be most consistent). This creates a blade that is hard enough to stay sharp, while being much less brittle (so it won't shatter of you drop it like a file would). Depending on the temperature you use to temper it, you can make it varying degrees of hardness, I chose 250C as it is supposed to result in a Rockwell Hardness of about 58 (ish) which is meant to be about right for a bushcraft knife.



There are people on the Internet who actually understand this and there is loads of information out there so I will let you get any further information you require from the Green Pete Knifemaking Video and from other Internet sources, I'll just stick to describing what I did.



1) Preheat your domestic oven to 250 Celsius. In fahrenheit that is 482 F.



2) Holding the blade in locking pliers, heat up with the gas torch until cherry red. Then start checking with a small magnet if it is still magnetic. Once it loses it's magnetism the structure has changed, hold it at this temperature (judged by colour I suppose) for a few minutes, then plunge into a bucket of oil AND COVER IT (in case it flashes into fire!!!)



3) Remove and wipe down. Sometimes the metal has distorted a little from this process, mine acquired a small twist to the left less than 1 degree and I was happy to ignore this. I suppose if it was worse you could try re-heating it to above the critical temperature again and re-quenching but I'm not sure if this causes weakening.



4) Stick it in the oven at 250 C (482F) for 2 hours, then switch off and allow to cool slowly.



5) Sanding and buffing again, to remove all the black stuff!