Quench oil life

[Bailey Knives]

I have Parks 50. A good quench oil that I have been using for a while. What is the expected life from this type of oil? I am not a metallurgist, but want to get the most out of my steel, with the stuff I have, and want to make sure that the oil I am using is not too old or worthless.

 

[Ed Fowler]

The way it was explained to me many years ago, the more additives you have in your quenching oil the quicker it would have to be replaced.
I don't know about Parks 50, but my Texaco Type A has never shown any indications of wearing out, it is pure mineral oil of a specific weight.