Using Motor Oil

[BIGBAMAK5]

I read in "The Blacksmith's Craft" by Charles McRaven that you can use old motor oil to quench steel and it will turn it black. It said in the book that it would probably catch fire. I have not read anything on this site about using motor oil. I have used it once to do some bolt heads for a mantle I was building. They turned out great and the wife was very happy. Just wanted to what you guys thought about this method and is there a better, safer way to turn the steel black?

Thanks,

Rush

[Woody]

Motor oil is an effective quenchant, but it can contain many toxic addatives that are vaporized when hot metal is quenched in it. Breathing the fumes can be hazardous to your body. Vegetable (cooking) oil is a much safer material for quenching steel. You should have a tight fitting lid handy for any oil quenchant tank in case a fire results and also a fire extinguisher at the ready. Although most of us have done it at one time or another, quenching steel in oil inside a shop or garage is not recommended. This is something that is safer to do in the open air.

Woody

[Roosko]

Hi Rush:

Oxford, Alabama here.

I use peanut oil for most of my quenching. Of course most of my quenching is on knives.

I have been known to add a little transmission fluid to the peanut oil.

Robert

[one_rod]

I use a random mix of gearbox / engine / hydraulic oils. Machine drainings from work. The boss would have to pay to get rid of this stuff so he is happy to see me take it home.

Have never had a fire in it from quenching red hot blades, provided you submerge the whole thing quickly. If you stop with half a hot item in the oil and the other half in the air then it will flare up.

If you just want to blacken an item, rather than heat treat it, then it can be done at "black heat". This is just cooler than dull red and should be below the flash-point of most mineral oils.

However, I always keep a dry powder fire extinguisher around the place, just in case.




one_rod.

[easilyconfused]

I'm not a fire-fighter, and most people probably know it but, for those who don't, I figure now is a good time to point out that smoothering is the only way to put out an oil fire, either by a tight lid, a powder fire extinguisher, etc. NEVER try to put an oil fire out with water. That just leads to a flaming puddle spreading around your shop. .

[irnsrgn]

I believe your question was about getting a black finish on something.

I use a combination of used engine oil, gearbox oil and hydraulic oil for a nice black patina, the best black patina is gotten by quenching at just red in a dark place, too hot and the black patina gets too hard and either cracks or gives an uneven finish, with white spots. I get a flat black patina by holding it above the forge fire till the oil dries, sort of bakes it on.

[Strine]

We eventually go the way of all flesh. I'd rather it be through old age than through sniffing carcenogens in the fumes from old engine oil. But heh, each to his own. Bear in mind this snippet comes from a ticketed blacksmith-come-oil specialist and not a medico. But then what quallies do I have to refute such claims.

You can get a satin black by holding your piece over gently burning pine sticks as another alternative. I haven't tried other woods but radiata pine seems to work OK.

[Ten Hammers]

I use crankcase drain oil from my truck. I also use Watco Danish oil. I also use cheap olive oil. I also use mineral oil. I also use wax. I also use veg oil. Do this by a door, and have a fan blowing out ( not a little fan ). Be upwind and do not breathe the fumes. Like Woody said, an extinguisher should hang by the forge and the container of oil should have a snap tight lid ( this is not a plastic container ).

[BIGBAMAK5]

Thanks for all the great info guys, very helpful.

[ApprenticeMan]

If you take one of those old pump bottles of oil, and then heat up the peice you want to blacken to just below red heat, then just pump the oil onto it while holding it over soemthing to catch the oil. Then rub it on with a thick used rag, as it will still be hot, just use quick brushlike strokes.