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-----:Clearcoat Bluing/Black Oxide for everyday residential use?
Quickstart:
"Bluing" (also called "black oxiding") is a process where parts are immersed in a very hot (230+ °F) solution, heavy in caustic soda and nitrates and/or nitrites to build a stable black rust on them. If the parts are rather matte to start with, they'll usually look black; if the parts are highly polished, they usually come out with a jeweled navy blue look.
Although bluing is not very corrosion resistant except when waxed or oiled, it is attractive, and the coating is very very thin, almost never affecting any clearances or tolerances.
"Cold bluing" / "room temperature blackening" is a process which simulates hot black oxiding, but is not as corrosion resistant, thin, or free from smut.
Q. I am an architect interested in the variegated aesthetic of the black oxide process for a plate steel handrail I will be fabricating for a residence I am designing. Painting and other attempts at "imitating" this look have proven unsatisfactory. I have only a cursory knowledge of metallurgy. Is it possible/necessary to apply a clear coat after the finishing (will the black oxide rub off through wear), that will retain the appearance for a degree of longevity and keep the finish inert?
Thank You.
Jonathan Kurtz- Cuyahoga Falls, Ohio, U.S.
2002
A. Black oxide has very little corrosion resistance, and most of what little you see is from rust preventative oils used with it. If you want black oxide on a handrail, unless you want to wax it very regularly, I don't see an alternative to clear coating it.
But as Jeffrey Homes warns us elsewhere on this thread, by the time you add a clearcoat to black oxide, you may be right back to where it looks like black paint again 🙂
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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? Have you thought about black nickel or chrome?
Steve Delaney- Ontario
Multiple threads merged: please forgive chronology errors and repetition 🙂
Best clear topcoat for black oxide?
Q. We have a request for small black oxided steel parts with good corrosion resistance.
The required finish is more cosmetic than functional and we thought of dip coating these parts in a clear, low viscosity resin just after the blackening process.
Which type of resin would be better? Epoxy, Polyurethane, Acrylic?
Any suggestions on where can I find it in the EU? My recent experience shows that importing "dangerous chemicals" from the US into Europe can be a long and tricky process...
Luis Henrique Godinho
RIREV, Lda - coating shop (PVD, WS2) - Vagos, Portugal
2005
A. I think that you can use Paraloid B 44 acrylic resin (7,5% solution-75 gm Paraloid B 44 dissolved in 1 lit toluene) !
Good luck!
- Cerovski vrh Croatia
A. Hi Luis. I'm not experienced with the specific acrylic Goran suggests, but you obviously must not wax or oil the black oxide before any further coating ... and without those protectants it can flash rust in 1/2 hour. So your "just after" is critical. The black oxided parts parts should be clearcoated immediately.
However, 2-component clearcoats are better than any dip or single part coating. You can use 2-part polyurethane automotive clearcoat or, if not exposed to UV light, epoxy. Good luck!
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
Multiple threads merged: please forgive chronology errors and repetition 🙂
Black Oxide Handrail
Q. I am designing a steel stair and railing. I am very fond of the "Black Oxide" finish. Which seems to be commonly known as gun metal finish? I clearly only have a very basic understanding of the processes involved. I have had some material science courses in college, so I can grasp some of the technical issues. I have a few concerns about the "black oxide" process in regards to my design. The parts are to be welded together. It seems to me that the oxidation would decrease the weld strength. Is it advisable to weld "Black Oxidized" parts? Should I consider mechanical fastening or oxidizing after welding?
My other concern is the durability of the finish on a handrail, apparently it is suspect. It seems that I will need to "clear coat", which from what I have gathered from the finishing.com website can be as simple as a polyurethane. Are there special concerns when "clear coating" Cold Black Oxide, since it can rub off easily? Or is there a smarter solution to the design problem? Any help you can offer will be greatly appreciated.
Thank you,
Jesse HR Young- Des Moines, Iowa
A. Black oxide is very thin, and will wear through easily. It also offers little corrosion resistance unless topcoated with oil, wax, or, in your case, a clear finish. The automotive polyurethane clear coats are very durable and should do what you want. No problem to black oxide weldments.
However, once clearcoated, It may look just like gloss black paint.
Jeffrey Holmes, CEF
Spartanburg, South Carolina
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