Now put it in the kitchen over at 350° F to 400°F .for an hour. If you temper at 400F you will get more sparks but it will not last as long as tempered at 350°
This worked great for me on a frizzen that was too hard, but I put it in a soup can filled with fine sand to stabilize temps (saw this idea on the old, old board, I think). My oven was surprisingly stable, but I monitored with a separate thermometer as well. I did it a couple of times at least before I got the spark I wanted, ended at around 390, I believe. It was amazing that the temper colors were spot on for the oven temp, although I guess it shouldn't be.
Later I took it back to the maker for some new springs, and they asked how I got it to spark so well when they tested it.