It has been a number of years since I have made a spring, but made several in the past. All that I have knowledge of are still working. These were all heated (by color) with a propane torch & quenched to harden & then tempered by the oil burn off method. When possible I would suspend the spring on a piece of wire rather than holding it in pliers & concentrate the flame on the thicker areas & let the heat run to the thinner ones.

Worked well for me for the number of springs I needed to make with minimum expense for set up. Of course if one is making a lot of springs on a regular basis then a more sophisticated set-up would certainly be advisable.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra