what oil for blackening steel?

I remember reading some where(RCM?) that you can make a black surface finish on hot steel by applying oil. Anyone know what kind of oil to use. I'm guessing it is like seasoning a cast iron frying pan.

Reply to
dan
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Linseed oil works. Dab it on with a small piece of cotton rag. The steel needs to be hot enough that the oil smokes and carbonizes while you're applying it. Wipe off the excess when the piece is cools. A coat of paste wax adds some protection and seems to make the finish darker.

Reply to
Ned Simmons

Does it need to be hot? I have had good success with Birchwood Casey's Gun Bluing paste. It is an easy cold application and with the paste (rather than the liquid) the results are less patchy. Some sort of oil/wax finish over it is recommended.

Reply to
Michael Koblic

Boiling the steel in sodium thiosulphate solution, photographers' "hypo", also works. I just saw a reference to "black oxide" that mentioned caustic soda at 140C.

Reply to
Jim Wilkins

And if you use Linseed oil on a rag do something like burn the rag after use. Linseed oil on rags is prone to spontaneous combustion an can light up later on if you just chuck it in the bin.

Reply to
David Billington

Used motor oil works too. I've quenched in this from red heat and you get a great black finish after buffing.

Karl

Reply to
Karl Townsend

Old-timey blacksmiths used to "blacken" iron by heating it to about dull red and quenching it in HORSE MANURE. Then, wiping it with oil of some sort.

Yep, the softer it (the manure) was, the better. The thought then was that the carbon that was added to the surface made it black. Blacksmith's shops smelled that way for a reason !

The most modern method for it is used motor oil, natural, not synthetic. Back in the days before there were so many "non-petroleum additives" to the gasoline and the oil, it worked better.

But it still works. Hardens (depending somewhat upon the alloy) and blackens at the same time.

Flash

Reply to
Flash

When I was in tech. school, we had a 45 Imperial Gallon drum of motor oil for this.

Steve R.

Reply to
Steve R.

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