I was at a hammer in last weekend and the resident smith was going to quench the edge of a tomahawk. He pulled out a shallow pan, about 8" x 10" x 2" and there was a brownish paste in the pan. I will not get too descriptive but you can imagine my first thoughts. He took out the heated hawk and put the edge into the paste and it melted and flared up. It was a mixture of motor oil and parafin wax. He said it was safer than keeping liquid oil in a can as it did not spill once it cooled and solidified again. Seems to have done a good job of quenching the edge of the hawk, too.

Something very similar is described in Goddard's $50 Knife Shop

Interesting. I wonder if it would work with less potentially toxic oils?

Try Tallow (rendered Animal fat) in a can, it will melt then resolidify

I have quenched things in my beeswax/linseed oil mix a few times when I have been away from the shop and was afraid to use water.

I was at a rendezvous one time and a guy wanted me to reharden the frizzen on his flinchlock because it was too soft and not working well for him. I hardened it in the wax. Don't know what the steel in that thing was but it was still too hard to spark right even after I drew it back to bronze, purple, and then back to blue TWICE. Ended up drawing it past blue and worked great. He went away a happy camper.

Remember the only important criteria for a quench are:
1) Safety: Flammability, toxicity etc
2) The speed of quench. Faster is harder unless it is too fast then it may break the steel
3) Uniformity of quench. If the steel is cooled non-uniformly it may fracture the part. Circulate the quench or move the steel around in the quench liquid to assist in uniformity of quench.

Many factors determine these criteria. As an example a thick gear only will be a slower quench than ATF fluid. This is due to ATF being less viscous and will move around more readily in the quench process, exposing the steel to fresh unheated oil than if the quenchant were heavy gear oil.

Remember: Brine is faster, water but more uniform. Items that fracture in a water quench may survive a brine quench.