There is an excellent tempering trick for top lever springs if you have access to an old supply of sperm oil (big if) and a torch. The flash point of sperm oil happens to coincide with the ideal tempering temperature for carbon spring steel. The hardened spring is dunked in oil and then heated evenly in the torch flame until the oil just begins to flash (ignite). The torch is played on the spring just enough to hold the spring at the flash point for 30 seconds or so and then allowed to air cool. The 'smith who taught me this trick had tried some synthetic lubricants, but the flash point was wrong. In his experience, it has to be the genuine whale stuff. It works for me.
