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How to Blacken Stainless Steel
Hello, I'm looking for information on the processes available for blackening stainless steel. If you could direct me to any publications or services, I would greatly appreciate it. Thanks,
Terry H [last name deleted for privacy by Editor]UC Santa Barbara, California
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- The Metal Finishing Guidebook lists 3 formulations of blackening baths for stainless steel, Terry. The one that sounds simplest to me, although I can't comment on its efficacy, reads:
- Sulfuric acid, 180 parts
Water, 200 parts
Potassium dichromate, 50 parts (Potassium Dichromate [linked by editor to product info at Amazon])
Operating temperature, 210 degrees F. -
- Proprietary processes are available from such suppliers as:
- Electrochemical Products Inc. (EPI) and
- Heatbath
There are also stainless steel anodizing processes offered by B&M Finishers and a stainless steel black passivation process offered by Russamer Labs. Good luck.
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 Ted Mooney, P.E. finishing.com Brick, New Jersey |
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Terry,
Your question did not specify what purpose the blackened stainless steel is to be used for.
Some of the components inside a TV tube must be "blackened" using a process of heating and cooling in a controlled atmosphere.
Leslie R Williams- England
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Ed. note: Please listen to Leslie, folks. People get the most rewarding answers to their questions if they employ the reporters' creed of "who, what, when, where, & why" when posting their question :-)
September 14, 2011
If you heat stainless with an oxy-acetylene torch (neutral flame) until it has an orange glow uniformly, then let it cool naturally it will remain black. Polishing with steel wool and metal polish enhances the finish. This is for cosmetics only. It is a very hard finish but will scratch with sharp objects. It is black about .002" into the metal.
Repeat the process again with a warm water quench and some stainless will harden. The blackening occurs because the chrome and nickel are being burned out. The remaining metal seems to be the same strength, toughness etc.
Audit Service - la mesa, California, USA