I was given 4 gallons of food grade hydraulic fluid. I have some knives my mother in law wants me to make for an upcoming show she is doing. My question is, will it be safe to use as a quenchant and anti rust coating on said blades? Thanks in advance.

~The Mad Rabbit

Olive oil or canola oil (stay away from soy and peanut, as the former oxidizes and peanut allergies) are classic, as is warm lard and tallo. Hard to tell what hydraulic fluid will do when exposed to red hot steel. Might not be an issue may be safer than Margarin but why take a chance?  

What is the flash point?

Since blades are ground, and polished afterwards which removes the surface that came in contact with the oil, there shouldn't be a problem.

I'll get the information from the barrel it came from while at work tomorrow. My initial plan was to use it to season (like cast iron) the blades as well, being as that is what was asked for. But it wouldn't be a big deal at all to do that during the tempering cycle with veggie oil. 

~The Mad Rabbit

I sure wouldn't use it to temper cast iron or finish for a food contact utensil. WAY too much liability not to mention you have to be able to look in the mirror and not hate what you see.

You can buy seasoning oils for cast iron now though I prefer to use a little rendered bacon grease. As long as you're going to grind after heat treating any food oil will be safe. I hit the local super market drop off a 5gl. water jug and ask them to fill it next time they change the fryer oil. It's never taken a week to get it filled and they LOVE helping a blacksmith. I just ask nicely and tell them what I'm doing with it. the folk in the kitchen like me better than the guy turning it into fuel. It really helps being a likable BSer sometimes.

Just don't take chances with people's health if you don't KNOW don't do it.

.Frosty The Lucky.

I took Frosty's cue and got a 6 gallon bucket of used fryer oil from the grocery over the weekend. Lent is a good time to ask... smells a bit fishy though

 

 

But it wouldn't be a big deal at all to do that during the tempering cycle with veggie oil.

​What steel? I'm thinking that to get hot enough during tempering for the finish to stick you'd want at least something like A2 or D2?
I've noticed canola doesn't stick at all unless I use it as a quenchant. (1095, L6)

Use a food grade wax to finish. Carnuba is food grade, digestible and hypo allergenic. It's the shiny coat on pills to make them go down easily. It's a darned tough finish, stomach acid is what dissolves it off pills and M&Ms.

Oh come on, you didn't REALLY think they invented a sugar shell that wouldn't melt in your hand did you? We've been eating carnuba for probably the last century as a matter of course.

Frosty The Lucky.

We used beeswax at the Jelly Belly Candy Co. for the polishing process.  I missed out on half of a small fiber drum that they tossed because it was too old for food regs.