Durable black coatings for stainless steel

A. Hi A. It is true that we avoid discussing proprietary products here whenever practical, thanks ( huh? why?)
Safety Data Sheets for the majority of chemical products are usually easy to find on the internet: just search "Safety data sheet [plus product name]" or "MSDS [plus product name]" and you'll usually be able to figure out the general technology behind the product. My guess is that the light blue color is due to some copper sulfate content.

"Cold blues" are usually selenium based, not usually considered very durable, and smuttier than hot black oxide is. That's not to say they are never appropriate, just that there are many applications for which they're not. Further, soaking stainless steel in HCl is usually not considered a good idea because stainless steel is highly subject to chloride corrosion.

Please introduce yourself, and the application lest we follow the will o' the wisp into a swamp of ever less appropriate ideas. A washer manufacturer, for example, would usually send such washers out to a plating jobshop for hot black oxide whereas a hobbyist with a small handful might not. Cold black oxide might be fine for machine parts, but probably not for decorative parts on a motorcycle (in fact black oxide in general probably isn't). Black oxide will usually require wax or oil for corrosion resistance, etc. Thanks.
Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Hi again. Copper-Selenium based blackening ought to be okay for that use, although I am not personally familiar with their use on and adhesion onto stainless steel as opposed to carbon steel. Other brands of similar products in smaller containers are available in the $10 range, and are perhaps available at a gun shop with no shipping cost.

Nobody will risk criminal prosecution for theft of trade secrets by telling you the exact proprietary formula a particular vendor is offering as a result of their R&D, and we can't help crowd-source such an enterprise anyway ... but I doubt that you can assemble the needed ingredients for less than the cost of the mix -- although you're certainly welcome to try.

Muriatic acid is essentially hydrochloric acid at a lower concentration and with looser standards regarding contaminants. It probably can be substituted. I haven't seen the directions you refer to but I doubt they intend immersion in HCl of actual 50% chemical concentration anyway -- that's awfully strong.
Good Luck!


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Cold black oxide:

Selenous acid 6 gms
Copper sulphate 10 gms
Nitric acid 4-6 ml
water 1 lit

(according to Fishlock,D. Metal Colouring,Teddington 1962,p. 242) →

A. Hi again.
Whether copper-selenium room temperature blackening "can be done" on stainless steel probably depends on:
• the type of stainless steel,
• your standards (hobby platers may not demand the level of quality a manufacturer who is warrantying a product must), and
• whether you are willing to expose stainless steel to high concentration HCl. That would be a hard no for some, and a let's try it for others :-)

Fishlock's "Metal Coloring" does not appear to be on line; but if you really want to see it, and can't afford to buy it, it is available in at least 92 libraries around the world.
Readers wishing to find a copy near them can try worldcat.org, which pretty easily locates even the most esoteric books (although some books are obviously so rare that traveling to a library that has them can be prohibitive).
Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. A black oxide coating is a very good way to blacken ss parts and they can be done pretty inexpensively by many plating & finishing jobshops. A quality after-finish coating is paramount to achieving a lasting, quality finish.

A. Yes, stainless steel can be black oxided. Whether it is the best way to blacken stainless steel though depends on your actual situation; so if you want some other options reply with more details please.

A. Hi.
Saw your request re blacken stainless.
I work with stainless on a daily basis and tried a few methods to clean up TIG welds, one being an acid based cleaner without DC current.
There was a hydrochloric acid I tried on a stainless weld that was used to clean aluminum welds; I left it soak/submerged in it for about 1 week it went all black.
As far as staying that way for a period of time I don't know as I threw it out.
Another way way would be to put the object in front of flame or a furnace; we recently had some fire-affected items returned to us that were all black. We tried electropolishing them at professional finishing bath and the worst ones didn't come clean, they stayed black. But the problem you will then have is the heat will alter the chemical/metal composition of the stainless steel, probably depleting the chromium in it and it will most likely rust and fail.
You will need to try a few tests and let the material weather.
Hope this helps, good luck.
Brendan Mackenzie
- Vic, Australia
August 16, 2009

A. Whatever you do will be temporary, Ryan, since the frets themselves will wear down, and any coating on them will certainly wear down sooner. Fairly robust blackening of stainless is possible in a molten salt containing sodium dichromate. Decades ago I visited a shop which offered many different varieties of molten salt processing, but it may be hard to find someone offering that process today. Black chromium plating on steel should be reasonably durable. You can anodize titanium easily with very mild electrolytes but the colors are diffraction coatings (partial wavelength thickness), so I wouldn't expect them to last long, but I see no reason you couldn't repeat the process regularly with a brush plating procedure that would not necessitate any disassembly. Ted Mooney, P.E. Striving to live Aloha finishing.com - Pine Beach, New Jersey A. Try black chromium--but you must find nearest plating shop--that is a job for professional plater. Hope it helps and good luck! Goran Budija - Cerovski vrh Croatia

A. http://www.basscentre.com/cat/product_info.php?products_id=1338

This site (in London) offers black frets as well as gold and bronze. They may be able to help you with frets that are already designed for guitars. Whether they are plated or not will require correspondence with them.

A. Black metal was created in an optics lab last year at the University of Rochester by Dr. Chunli Guo.

I was fortunate enough to read of the discovery and contact Dr. Guo regarding the process. Guilford Guitars (google them) is currently building me a guitar which will have the world's first Black Metal frets (the guitar is dubbed, "The Black Rocket").

You may wish to also contact Alan Wald at Buzz Feiten Design, I believe that they will be featuring the guitar on their website when finished. It may also make an appearance at NAMM in 2008. There is a possibility that they may offer Black frets in the future - depending on the market for them and the costs involved in bringing the idea to market.

Please feel free to contact the University of Rochester Office of Technology for more information on the Black Metal Process. They were extremely nice people and are looking for products that can utilize the "Blackening" process.

Aside from the black guitar frets (which I am pretty sure was NOT their primary market) Dr. Guo's process should have many, many uses in the future and I imagine in 5 to 10 years it will be a fairly common process to many metal finishers. So be the first on your block to own a Femtolaser and start blasting away :)

Best always,

Thanks, Larry!

Although this particular poster and the responders are talking guitar frets, the site is about metal finishing -- and that is indeed a very exciting development in metal finishing!

An alternative approach to true black is amorphous electroless nickel plating which can produce a sponge-like surface whose crevices capture essentially all light. But the laser process sounds like an alternate approach for super high surface area with the advantage that it can be done on any base metal, not just nickel plating. There may be situations where, for example, the corrosion resistance of gold or platinum is required, and electroless nickel won't suit.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Hi, Bill. Black chrome plating, black nickel plating, and black electroless nickel plating are only coatings, but they are metal and I'd expect them to be reasonably durable. Black ruthenium and black rhodium are precious metals, so more expensive.

Regards,

A. Hi, Peter. I personally don't think truck bed lining has much possibility of success as a coating for guitar frets. It's not metal, so the metal strings will be much harder than the fret coating is, and will wear through it quickly. Plus, it's a bit thick and gloppy; on a good guitar the strings are very close to the frets, and may rub against such a coating and be dampened.

Regards,

A. Try attachments.wetpaintserv.us/ZLSnLKosv0l3CnE9hGDi7w488720
-- there you can find small download free handbook on metals colouring and plating, including Stainless steel chapter. Hope it helps and good luck!

----
Ed. note Jan 2017: Although wetpaintserv.us was a legitimate site when Goran posted it, it now appears to be a malware site. Don't go there!
Goran has been kind enough to upload his booklet to our library here at https://www.finishing.com/library/budija/budija.pdf instead :-)

A. Old and good oil blackening is simplest way to blacken SS. Oil it very, very lightly and then heat it to max 400 °C (slowly, you can use hot air gun). Any edible oil can be used but linseed is the best. Hope it helps and good luck!

A. Hi cousin Tanveer. Topic 19 "How to Blacken Stainless Steel" offers a chemical approach to blackening stainless steel which you might try. Also see letter 1754 "Blackening stainless steel". But the less machinery and consistency you can apply, probably the less reliably satisfactory the finish. Good luck.

Regards,

A. Hi Elizabeth. There may be other finishes that meet those needs, but porcelain enameling is the only one that I can think of :-)

Luck & Regards,

A. Hi Elizabeth,
It is possible to black anodize stainless steel.
adv. We have good success with surgical steel (420, 420, 440 alloy), sometimes 304 alloy is anodized in good black. The anodized black is bio-compatible. This technology (as long as colored anodizing) has been developed for medical instruments for color coding. The black color stands 500 °C, but not sure how it goes on grill. Please see the images attached and russamer.com