Salt quenching baths are quite common and purified salt is most often used for the base so as to establish a stable baseline, from there the bath can be varied for specific properties/results by adding other minerals/mineral salts to it - not much different than changing the alloy of a lead bath to adjust its properties.
O-1 is "O-Oil hardening", salt baths are not required but can be used. As with anything else, the type of oil and additives/contaminants contained in it will adjust the resultant properties of the quench bath. Like any other quenching bath, the combinations are nearly endless and the results of quenching will be directly affected by the properties of the bath - new oil is not going to produce the same results as used oil the same as the results using heat transfer oil will be considerably different than those using mineral gear oil. One word of caution, if you're heating your oil bath, too hot and it can erupt with a violent explosion when the hot iron goes into it.
Quenching baths should not be confused with pickling or tempering baths, three separate and totally different operations however, it is often possible to produce a combination pickling/tempering bath so as to accomplish both operations at the same time. The melting point of relatively pure sodium chloride is around 1474°F, boiling point 2670°F.
The raise to temperature and hold times also have a considerable affect on the results - just getting the steel into the austenitic range is not enough, some alloys require defined raise & hold temps and times to achieve the desired results. A rapid response surface contact thermocouple will help eliminate a lot of error and blind guessing.
