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Ted Mooney, P.E. RET
Pine Beach, NJ
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for Metal Finishing since 1989
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How to achieve black mirror finish on stainless steel
adv.
Q. I have a flat discs, 100mm diameter, of thin (0.3mm) stainless steel sheet, perforated with 0.5mm holes. It's annealed 316 steel.
I want to make one side black (preferably matte), and the other bright and shiny. Whatever finish I use, it mustn't block the holes (although I don't mind if they are reduced in size a little).
The discs will be in vacuum after finishing, so corrosion isn't a problem.
I was wondering about giving them a wash of silver, then putting them on a flat surface and passing hydrogen sulfide over them, to blacken only one surface. But I'm unclear about how bright a silver wash would be.
Does this make sense? Would I have to give a copper wash first?
Or maybe there's a better way.
Thanks,
Hobbyist - London, UK
2007
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A. Martin, you can simply use diluted muriatic acid ⇦this on eBay or Amazon [affil links] applied by brush or sponge. Birchwood Technologies [a finishing.com supporting advertiser] also makes a blackening patina for steel to achieve similar results. Good luck  Barry Feinman BarrysRestoreItAll  Carlsbad, California  A. Oil one side very, very sparingly, then heat it to 300-400 °C (slowly). - Cerovski vrh Croatia A. Stainless steel is probably the most difficult metal to colour by the usual oxide or sulfide treatments.  Geoff Smith Hampshire, England |
Q. Hello There,
I am an art student currently working on a large metal sculpture. So far, it is a large stainless steel rectangular cube about 7 feet tall. It was fashioned out of extra scrap metal from out art department. I've run into a few problems. The steel sheets have a factory coating on them that became very mirror-like after experimenting with sanding. I wanted to achieve this look uniformly around the entire piece, but after grinding down my welds I have already taken off this great black finish around the edges.
I figured I'd have to sandblast the entire thing and re-coat with a metal patina. I ordered some Black Magic from Sculpt Noveau. I am deathly afraid that I won't be able to achieve the mirror effect from the factory coating. This project will be placed outside and will need to withstand the elements. Any help would be greatly appreciated!
Student/Sculptor - Darlington, Wisconsin, USA
March 2, 2011
A. The black coatings that I have seen are not shiny. I have seen kitchen knobs that were, but it appears to have been a very thin phosphate coating with a clear coat. It was not very durable. It might have been a black oxide. The product you mention is a black oxide. It will need a oiled finish. Look up rubbed oil finishes on bronze.
James Watts- Navarre, Florida
A. That kinda sounds like mill scale to me - not usually something you'd find on stainless steel, but it matches the description. I make a standard practice of grinding it off on my structural steel (as it interferes with welding/coating/etc and doesn't protect the surface from corrosion) - it comes off easy with a grinder or low grit sandpaper. But if you take a higher grit - say around 100 - as your first pass it's possible to get mill scale up to a mirror finish like you described. Mill scale is basically just miscellaneous crud from the steel mill's roller heads, so there's really no way to 're-apply' it, but if it's any consolation it probably wouldn't have stayed on for long anyway.
George Portland- Detroit, Michigan, US
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