The authoritative public forum
  for Metal Finishing since 1989
-----

Which blackening coating to use

Hello,

I am searching for a blackening coating for low carbon steel that will be corrosion resistant. It will be for steel columns for a mobile pavilion (or stand) which is to be easy to setup and disassemble and with a very low or non existent maintaining; for that condition, simply painting the columns is not an option.

I have read about black oxide coatings which is are not corrosion resistant, and also about zinc and phosphate coatings which are very low corrosion resistant. Stainless steel could also be an option if necessary. The main ends are its architectural quality, that is the "blackness" of the steel and that it be corrosion resistant and wear resistant (though this could be reserved only for some rotating joints which could have a different coating albeit a black one).

Thank you.

Jesus Galvez
Architect - Madrid, Spain
October 20, 2009

You can use oil blackened stainless steel(oil it very very slightly with linseed oil/then heat it to 300-400 °C -- try it on some scrap)),probably stainless can be black anodized too.Black chromium plating can be used too(or clearcoated black nickel).Hope it helps and good luck.

Goran Budija
- Cerovski vrh Croatia
October 23, 2009

I thought only Aluminium could be anodized... Can stainless steel really be anodized or is the black treatment in fact a coating?

Jesus Galvez
- Madrid, Spain
October 24, 2009

---

There are two ways to achieve black color on stainless steel sheets. Inco and PVD. Inco is dipped and PVD is done in a vacuum furnace at high temperature, with various gases and sputtering targets. I believe PVD coating is a more permanent coloring process than Inco.... based on my information. PVD can be done on glass and stainless steel...not sure if carbon steel will pose to be a problem.

Michael Liu Taylor
specialty stainless steel distributor - Dallas, Texas
October 29, 2009

---

November 3, 2009

Black anodizing for stainless steel:
NaOH........700 gm
KMnO4.......10 gm
Na2S........1 gm
1 lit water
110-120 °C temp.,20 v,60 minutes
(according to Handbuch der Galvanotechnik [occasionally avail. from eBay, AbeBooks, or Amazon affil links], Muenchen 1966.)
Hope it helps and good luck!

Goran Budija
- Cerovski vrh Croatia