I do feel that I should point out a couple of things about using oil for tempering steel. I did not mention it in the posting because the likelihood of the average reader having at his disposal true tempering oil, they would more than likely be tempted to use Automobile oil. Tempering and Automobile Oil are two different beasts when it comes to plunging red hot steel into them. The smoke and fumes given off true tempering oil the toxicity is reasonable but Automobile Engine lubricating oil in the same conditions gives off far more toxic substances and therefor not recommended at all. Now "Silver Steel" Drill Rod will water harden and temper with no problems, well it is just a basic high carbon steel that Blacksmiths have been tempering with water for many hundreds of years.
Lets keep oil for high grade Chrome Vanadium Steels and HSS versions and just for the odd Wood chisel and small parts lets stick to rule of thumb and water in these cases we don't need perfection. Well as far as I am aware of breathing in steam is not detrimental to the human body.
I have been using cheapo vegetable oil from tesco's for quenching for years Damascus, never had a problem with it. Its cleaner to clean up than dirty old motor oil, and the only health risk is it might make you hungry for a plate of chips.
