Letter 7276

Stainless Steel finishing to achieve light purple or blue color 

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I am in the medical industry and am looking for a surface finish for 316L SS resulting in a light purple or blue color. Finish must be able to stand up to high heat and moisture when being sterilized in an autoclave. Because of high use, it should not scratch easily. I have heard the term "blue ion plating" on SS, but have not had any success finding additional information. Thanks in advance for the help.

John Koontz
- Irvine, CA, USA

I haven't heard of "blue ion plating" either.

Give it a couple of weeks, though, and every search engine will lead people who are looking for the term right to this here letter .

But I am familiar with an anodizing process for stainless steel that may be what produces this finish. It's called "Prismatic Finishing" and is available from B&M Finishers [Kenilworth, NJ].

 
Ted Mooney, P.E.
finishing.com Inc. - Brick, NJ

Electrolytic colour for SS(Ni/Cr 18/8):

H2SO4........1 lit
Na2Cr2O7......7,5 gm
7o-95 C/o,o6 A/dm2-1,3V, object=anode,cathode=lead

Colour sequence:brown-blue-yellow-redish brown-purple-green.

Budija, Goran
- Zagreb, Croatia

This is very helpful but what strength sulfuric acid?? more details if you could please.. thanks

Frank Gyuru
- Clearwater, FL , USA

You must use 1,24 g/cm3 (density) sulphuric acid! Today I think that alkaline process is better solution, and it is ROHS compliant:

NaOH.....700 gm
KMnO4....10 gm
Na2S.....1 gm
H2O......1 lit
temp.110-120 C,20 V
colour sequence:brown(3= min)-purple(40 min.)-black (60 min.)
According to Dettner/Elze :Handbuch der Galvanotechnik

Goran Budija
- Zagreb,Croatia

We are looking for recommendations on the most robust method of treating/coating a stainless steel sculpture to withstand outdoor exposure. Hopefully we could get multiple colors, not just black. However black is also needed.

Thanks!

Mark Lueker
builder - Loveland, CO, USA