Blackining Steel????

[jpfabricator]

Iv been commissioned to make a few steel pieces (app. 9"x 4.5"x 2") for a local craftsman. He wants a dark black patina (think cast iron skillet). I was going to experiment with heat and oil like a skillet would be blackened, but if anyone has a cheaper, and easier way, Im open for suggestions.
Thanks in advance.

 

[randyc]

Iv been commissioned to make a few steel pieces (app. 9"x 4.5"x 2") for a local craftsman. He wants a dark black patina (think cast iron skillet). I was going to experiment with heat and oil like a skillet would be blackened, but if anyone has a cheaper, and easier way, Im open for suggestions.
Thanks in advance.

Heat and used motor oil would also be my first choice. The following is an example but you already know what kind of finish heat/oil produces.



An alternative might be gun bluing. "Cold bluing" works pretty well if the parts are scrupulously clean and also warm when the bluing is applied. You can repeat the process a few times to darken the patina.



I'm not sure that it would be as black as a cast iron skillet but most commercial oxide finishes probably won't be that black either.

 

[RJSakowski]

Iv been commissioned to make a few steel pieces (app. 9"x 4.5"x 2") for a local craftsman. He wants a dark black patina (think cast iron skillet). I was going to experiment with heat and oil like a skillet would be blackened, but if anyone has a cheaper, and easier way, Im open for suggestions.
Thanks in advance.

You can buy cold bluing and browning solutions from Birchwood Casey. There are also hot bluing solutions. I have darken steel quite sucessfully by simply heating. Buff the piece, if desired, and heat until colors run. Allow to cool and put the protective finish of your choice on. I used either a urethane spray finish or an automotive top coat finsh. I did the antique door hardware in our house that way. You can get a very interesting patina. If you heat further, you will get a dark grey more like the cast iron skillet look. If you can't heat the pieces, the chemical treatment will give similar results although IMO it doesn't turn out quite a pleasing. If you use oil to protect the surface from rust, you will have to renew it from time to time. That is why I used the clear spray finish.

 

[machinistmarty]

used diesel oil works great

 

[Ed ke6bnl]

you are saying to use diesel fuel oil

 

[T Bredehoft]

I thot used diesel oil was that black smoke on the highway.

 

[Johnwright]

Iv been commissioned to make a few steel pieces (app. 9"x 4.5"x 2") for a local craftsman. He wants a dark black patina (think cast iron skillet). I was going to experiment with heat and oil like a skillet would be blackened, but if anyone has a cheaper, and easier way, Im open for suggestions.
Thanks in advance.

I have experimented a little and have had some luck with Phosphoric acid. I recommend that the part is very clean, clean with acetone then soapy water and rinse. Then (outside) heat phosphoric acid in a stainless container and soak the parts in the hot. Acid. Some metals darken better than others.

 

[John Hasler]

I have experimented a little and have had some luck with Phosphoric acid. I recommend that the part is very clean, clean with acetone then soapy water and rinse. Then (outside) heat phosphoric acid in a stainless container and soak the parts in the hot. Acid. Some metals darken better than others.

I've also had luck with phosphoric acid. Adding the black stuff from inside a couple of alkaline cells gives a much blacker finish. An advantage of phosphating is that the finish is corrosion-resistant (though not corrosion-proof).

 

[18w]

I have experimented a little and have had some luck with Phosphoric acid. I recommend that the part is very clean, clean with acetone then soapy water and rinse. Then (outside) heat phosphoric acid in a stainless container and soak the parts in the hot. Acid. Some metals darken better than others.

What temperature do you heat the phosphoric acid to?

Thanks
Darrell

 

[Johnwright]

What temperature do you heat the phosphoric acid to?

Thanks
Darrell

The temp that I used was well below boiling. It was probably 180 deg. F or so. It was producing a lot of steam that probably was not very healthy for these old lungs.