How do you blacken steel with oil?

[tmuir]

I remember doing this in high school and know it involves heating up the steel item and plunging it into oil but can't remember the finer details.
I've done a quick search but can't find anything here on it.

How hot do I need to heat the steel?
Will any oil do or are some better than others.

I'm making a simple tapping tool and want to give it a black finish and if I remember correctly the oil black finish inhibits rust a bit too.

Thanks
Tony

 

[jack404]

Tmuir

i have put some blueing and blackening formula's in the downloads section

and i have a pile of more older recipies for colouring steel (blueing blacking reds etc) let me know if you want em

may i ask how black you wish the item? it may pay you to do it with Magnesium oxide finish is you want real black, black

cheers

jack

 

[tmuir]

To be honest I hadn't really thought about how black.
I found a hammer I made back in high school some 20 years ago at my parents house a few months back and it I gave an oil black finish and consider it just has sat on a shelf for the last 10 to 15 years and it has hardly any rust I was planning on doing the same to my tapping tool.

This is my 20 year old oil blackened hammer I made in high school along with some other tools I made back then.
I'm looking for a similar finish to the hammer.
I'll now head over to the download section and check out the recipes.

 

[Tin Falcon]

Totaly unscientific here but a tiny bit of experienced observation.
A few moths ago I needed to make a part for my metalcraft scroll bending tool. For whatever reason the tool would not accept and grip the end of the stock. This thing was made in england 10-20 years ago but never used. so making my own parts and mods seem the best choice. Any way to the point. I made a gripper cam ,just a 1/2 piece of knurled drill rod with an off set hole. To heat treat I used the old welders fab shop trick of heating the part to a nice cherry red and quenching in used motor oil . This needs no tempering.
I heated to cherry red then quenched . This left a dark but somewhat crusty looking black finish so I wire brushed the part.This left some scratch marks and removed a little more black than I liked. So I dipped the part in the oil then heated just enough to burn off the oil then quenched again.
For what it is worth my used motor oil is a 4:1 blend of Quaker State 5w30 and marvel mystery oil mixed well for 3000 miles or so in a ford engine LOL.
The results give a very deep dark black finish.
Tin

 

[jack404]

Tin

you've reminded me of a old mix

40 weight motor oil, used, add 1 cup of graphite powder ( dry lube) per gallon is a good mix

put a sheet of copper in the bottom of the tub this does something but not sure what but makes the mix work far better, ( copper is ionic so maybe it helps the carbon atoms transfer?? just a guess)

thats a old old old but reliable black, no need to get to cherry red either a light blue tone to the steel is enough

stir the oil and graphite well if you can to keep the colour even

to get lighter coatings, heat the oil mix, the hotter the oil, the lighter the effect

lighter dips can be taken with the lighter heat to get the colour you wish ( smaller steps if you wish)

cheers

jack

 

[Tin Falcon]

Jack interesting
So happens I have a pint sized container of graphite powder that I picked up a long time ago at the ag supply. Dry lube for seeders.
I also have copper flashing.
Tin

 

[John S]

Try used engine oil out of a diesel.
The additives in the diesel hold the carbon in suspension so they don't build up in the engine.

It's what I used to use all the while but we did have 200 odd trucks clean oil doesn't get the same finish.

Heat to cherry red and quench, make sure you have plenty of oil so it doesn't heat up to much.

Keep the part submerged until it's cooled enough to bring out to stop the surface catching fire. Wipe the crud off, preferably back into the oil and lightly polish with some fine wire wool.

If you can keep the oil, I used to use an old saucepan, it gets better with use.

JS.

 

[Maryak]

A simple but effective way I have used in the past is submerge the part in used engine oil. Heat up and boil off the oil until almost all of it is gone. Leave everything to cool down naturally, ie no quenching. - That's it.

Do it outside or in a very well ventilated area and don't breath the fumes. Used engine oils tend to be carcinogenic, so please take care if U opt for this method. This method also works well for tempering springs.

Best Regards
Bob

 

[ksouers]

Lots of great information, guys. Thanks :bow:

I use Mobil 1 synthetic oil in my car. Anybody tried using that?


Cheers,
Kevin

 

[PTsideshow]

On blackening steel with the hot oil, Use boiled linseed oil, or any cocking oil. The problem with using used motor oil now a days whether it is car or truck is the heavy metals in it, and other contaminants that can be converted into fumes. As most will tend to over heat the metal to orange to red hot which isn't needed.
You shouldn't use synthetic oils as the polymers and other stuff in them can cause headaches and respiratory discomfort.
The biggest difference in the food grade oils, is the smoke point. With canola oil being one of the highest.

You only have to heat the steel up to around 500'/600'F and then spray, dip or brush(with a natural bristle brush, not plastic). You can repeat as needed to get the shade you need.

Also the various food type oils will give slightly different colors and shades from brown to black.

And of course for any one making BarBQue equipment or other food contact pieces. The use of a food grade oil is a must, it is also recommended for anything that a child will come in contact with as most things make it in to their mouths. Sooner than later. ;D

 

[tmuir]

Earlier tonight I thought.
'What have I got to loose'
So I heated up the part, I did it in partial sunlight so was hard to see how hot I got it but at a guess past straw, maybe a very dull red and dropped it in about 500mls of new engine oil (Is meant to be for the wife's car so don't tell her). got a bit of smoke and a little bit of bubbling. I left it in there for a few minutes until it was cool enough to touch and pulled it out and wiped it down.
I had the fore thought of setting the tin of oil up outside in the sand near my workshop to save stinking out my workshop or making me breathe in the fumes

It isn't a perfectly even finish but its good enough.

Sorry not the best of photos as I had to take it without a flash so the photo wasn't bleached out.

Will take another photo tomorrow in natural light next to the bar stock for comparison.

Nothing like a bit of suck it and see. :big:

This is the simple half of my first shop made tool, a tap holder.

 

[Kermit]

On blackening steel with the hot oil, Use boiled linseed oil, or any cooking oil.

That is the same thing done when 'blackening' an iron skillet or other iron cookware. If that is the case then the process can be done in the oven set for 500 to 550.

Peanut Oil is the best for a good food grade color of chocolate black on the iron and was what my grandma used on all her cookware.

I would think there is more to it chemical reaction wise with some of the recipes, especially the ones with added carbon like graphite and the iron at a much more chemically reactive 'red heat'.

A comparison of the two coatings on similar iron pieces would be handy right here.

 

[firebird]

Hi Tony

Have a look at my tapping tool topic, This should be the link, http://www.homemodelenginemachinist.com/index.php?topic=2237.0

It will show in detail how I blacked all the parts.

Cheers

Rich

 

[tmuir]

Thanks firebird.
Its hard to get supplies in Western Australia, especially chemicals as a lot of stuff can't be posted so thats why I just went for the oil method.
It's not perfect but its good enough.