Oxidation and contamination are the issues to be concerned about. I would like to take this opportunity, and every other I can get, to once again stress and warn folks about the perils of edge quenching into really good quench oil. Really well made quench oils are dialed right in to do a job right, they are dial in with proper chemistry and viscosities, and any adjusting of this condition is most likely going to reduce their performance. Edge quenching often results in flare ups and flaming, this will heavily oxidize the oil and soot it up. Parks #50 has been labeled as "idiot proof" by some and nothing could be farther from the truth. A fine calibrated tool needs a skilled hand to use it properly and keep in good condition, any fool can use a $2 Chinese wrench with no worries. So far everybody who has tried a good quenching oil has reported back to me about how they were so impressed that they now fully see the difference, but I am still holding my breath and waiting for that guy who spent the money on some #50 and then burned it into tar and left mounts of contaminants in it, and then gets in a stump to tell the world it is a scam
. Canola oil is much more idiot proof than Parks #50.
If one keeps good oil in the proper working range, 100F- 150F, you should expect years of life for the size and volume of pieces we work with. Water is an issue as well and should be kept out of the oil as much as possible. Contamination of heavier particles are not so much a problem and can even be filtered out.
Every 6 moths or so I drain off my #50 and clean all the salt particles out of my tub. Others who do clay quenching do the same. If it is large enough to settle out it is not as much of a threat as something in suspension that can involve itself in the quenching process.
For all of these reasons it is best to keep your oil covered when not in use. The real nice thing about Parks oils is that they are clear with a slight amber color, so that you can see any contaminants in the oil. I have gotten to where I do not like quenching into anything that is not crystal clear and clean looking, thus some of the Houghton oils take some time for me to get used to.
