Fool proof???
To harden and temper springs, this is how I do it. Fill a coffee can up halfway or so with the lightest oil you can find (I use WD40...the only use I have for the stuff). Warm it on a coffee pot warming plate to about 110 degrees. It does help, though I don't recall just why. I believe the ideal temperature is supposed to be 114 degrees or something like that..
Heat the spring to bright orange (non magnetic) and quench edgewise. The spring will now be reasonably hard....or it should be. Some maker's springs harden more easily than others...I don't know why. They're all SUPPOSED to be made of the same stuff.
Polish the spring off and then, with a propane torch, heat it lightly all over, going through all the colors, brown, purple, blue, light blue, to deep blue gray. Make sure it's even all over and then set it on a brick or something that won't draw heat and let it cool. Now you have a spring. :wink: