A couple things about blackening steel

bear with me as I'm just a hobbyist- If i have any serious flaws with what I'm doing let me know

I have some small (OD 1.5" ID varying .5" or a bored cone) steel parts I want to coat without paint, (cheaply and relatively safely)- I read many archived threads about blackening steel and found many alleged possible methods. I decided to try the following: heat with a propane torch until a dull red, then submerge into corn oil and wait for bubbling and smoke to stop. Then heat to red and submerge again. Then take out and burn off oil and allow to cool slowly.

The first time I did it I misread the post and after the second submerging i took it out, wiped off the oil, and cooled it in water (I was impatient) It left a matte dark gray finish with a blue tinge in the light that I was rather satisfied with (although I'd prefer really dark black) That was a couple weeks ago- I noticed some spots already starting to oxidize (rusty colored- not black) today so I went back to the archives and realized what I did wrong. I again heated until dull red and submerged twice then tried to burn off the extra oil. This time some of the surface had a similar nice finish as before although darker and more even- however some of it had a jet black shiny covering that I really liked. I suspect that the shiny black was carbon residue left from burning the oil but I'm not sure.

Most importantly I want an even finish that will be rust resistant. What can I do differently to get that surface?

Part of my problem may be I sometimes work at night, sometimes during the day. The propane torch is not hot enough to make the steel visibly red during the day so I guesstimate when to dunk in oil, however at night I can see it glowing. Should it be glowing red even in broad sunlight?

Any suggestions with this method?

One last related question. Using the propane torch with something like that, what surface would you recommend working on? Slate chips and sends sharp shards when too hot, should I be on stone? Thick metal? What about a slab of concrete (making sure to minimize air pockets)?

Thanks for any help, I need it Jonathan Battat

Reply to
Jonathan Battat
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Jonathan Battat wrote: (clip) Should it be glowing red even in broad sunlight?(clip) ^^^^^^^^^^^^^^^^ I think one reason blacksmith shops are always dimly lit is that is the best for judging the temperature of steel. In full sunlight, the steel has to be practically burning up for the color to be seen. In a dimly lit room, you get so you know just how soft the metal is, how hard to hit it, how much longer you've got before you need to reheat, etc.

I realize that all of this applies to forging, not to blackening, but I think, for consistent results, you will need to know the metal temperature better than you can in full daylight.

Reply to
Leo Lichtman

In lieu of that, a pile of sand will work if your torch doesn't blow it all away. :)


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Reply to
Tim Williams

ideally u want some refractory brick (i think its called) its very light and doesn't soak the heat away but rather reflects it back to the work. The stuff is just a little more dense than styrofoam and crumbles very easily. You can heat it for ages and the back side will still be room temp whereas fire brick acts as a heat sink and will be hot.

I've had success with oil dunking - as i recall the work was heating higher than a dull red in a dark room - why not do some experimenting with small pieces at higher temps? I don't know the size of the torch or length of the work piece but with propane and refractory brick underneath and around the work higher temps should be possible

hope it helps


Reply to

2a) I've found that putting the container with the solution, and the parts, into the water of an ultrasonic cleaner will drive the reaction strongly and I get a good thick coating within moments. 2b) Uh oh. I've been pouring the used solution back into the bottle for about ten times now - I purchased the smallest bottle that Brownells sells, which is about the size of a large pill bottle. Other than carefully decanting the blue liquid into my beaker when using it, so that the red residue at the bottom stays behind, and then rinsing that out before pouring it back, I've taken no other precautions. It does still seem to work fine though.


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Reply to
jim rozen

NB: when diluting acid, always (a) wear eye protection and (b) always, always, ALWAYS dilute the acid in the water, slowly, with lots of stirring. Never pour water into strong acid - it will overheat and splatter the acid.

Any time I have trouble remembering this, I ask myself if water or acid is the better conductor and dissipator of heat. The answer is (clearly) water, so one in a case where a lot of heat is generated, I want to add a small amount of acid to a large amount of water so that the heat can be easily absorbed by the water.


Reply to
Alden Hackmann

If you have been using propane, change to a MAPP gas instead. The fittings are the same and the gas is intended for the portable torches as a higher heat variation.

-- Bob May Losing weight is easy! If you ever want to lose weight, eat and drink less. Works evevery time it is tried!

Reply to
Bob May

a saying to remember Good Johnny chemist does as he oughter and adds the acid to the water..

Reply to
Thompson Family

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