Heat-treating has two parts: hardening and tempering. Hardening occurs when the blade is brought to a critical temperature (depending on the type of steel) and then quenched in a liquid in order to cool it quickly and form a rigid molecular structure. I was going to quench my blade in oil, which would cool it slightly slower than water in order to reduce risk of cracking or warping, but still fast enough to result in desired hardness. So, I made this quench bath by TIG welding some tube to a 1/4" steel base and filling it with canola oil.
The only certain ways of knowing whether a blade is at critical temperature are color and magnetism. Once the blade is no longer magnetic, the molecules are ready to form their rigid structure in the quench.
Due to the thinness of the blade, I had to correct many warps occurring from gravitational bending while holding it in the forge to heat it up. I learned that I had to rotate it often, as well as drawing it in and out to heat the blade evenly. Most of the process of forging a blade looks like this anyways:
When it was evenly heated to nonmagnetism, I plunged it into the bath amid a gout of flame! I had to be careful that it was pointing straight down and that I did not move it from side to side in the bath, as these would invite warping because of the uneven hardening of sides, like the warping of my shield with the glue. It also helped that I put a hot poker in the oil beforehand to heat it preliminarily; ideally, the oil is hot to provide for less shock in the quench, like using oil instead of water. Just another precaution.
After the blade was cool, I drew it out of the quench bath and scraped it with a file to see how hard it was. I couldn't make a mark!