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Using Motor Oil

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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

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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

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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

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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.

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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. :).

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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.

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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.

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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 ).

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Like Roosko I use Peanut oil. I have many friends that like to fry turkeys and things in the large turkey fryers. They always are looking to throw out the oil. I provide them a bucket and get the stuff for free.

I let the used oil stand for a few days and all the debris in the oil from cooking settles to the bottom. Then carefully pour off the oil from the top. This will leave reasonably clean oil.

A benefit from peanut oil is the great aroma while quenching. Peanut oil also has a reasonably high flash point but will flash like any oil if you are not careful.

A drawback from peanut oil is that it will somewhat solidify in cold temperatures. I get around this by dropping some hot iron in it before I need to quench and it will liquify fairly quickly.

I have found that Peanut oil is a great all-around quenching oil and you get the blackened color on iron which is nice.

DanL

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As with many things, experimentation is the thing. I have used a lot of motor oil to do finish work. Nasty stuff. I have also used a lot of wax ( cake bees wax ). I must admit that olive oil ( Popeye finish ) is the best smelling I've used to date. I may try some fryer oil in the near future and see how that reacts and what the particulars are with it. Glad this thread got started.

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For those of you who use linseed oil, I heard that a rag soaked in linseed oil can spontaneosly combust. Is this an old wives tale or has anyone had this happen?

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Linseed oil is the only thing that will spontaneously combust....almost any oil, gasoline, oil based paint, mineral spirits, etc soaked rags have the potential to ignite, usually when you're not looking. Store in a metal container if necessary to keep inside, or hang up with plenty of ventiliation.

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I use motor oil for quenching knives, it works just fine as long as you don't breathe the smoke. The oil will light on fire when you dunk a peice in so wear good thick gloves when you do this. since water sinks below oil, i keep my oil in an old metal incense tube floating in my slack tub so spills aren't a problem.

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I use Johnson's old fashioned paste, floor wax, applied with a rag. It saves me mixing up a formula of some kind. I open the doors and windows when I use it, or I do it outside. The wax is getting a little hard to find, as is 20 Mule Team borax, so my last few cans I got from eBay. Boiled linseed oil is OK except that if applied too hot, you sometimes get a kind of olive drab color. A soaked rag can catch on fire and if it does, you'll drop it right away, guaranteed. Have something handy to smother the flames.

http://www.turleyforge.com

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