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topic 24076

Heat-produced Patinas on Stainless Steel and Chrome


A discussion started in 2003 but continuing through 2020

2003

Q. We am creating a show car. Rather than using the usual chrome engine parts we have decided to attempt coloring the bolts with heat. The assumption is that, with hardened stainless steel bolts, this method of coloring would give a hardness that will stand up to being turned by a wrench, as well as a finish that will not change. We desire to have yellow and blue colors in both stainless steel and decorative chrome. So far I have heated some hardened stainless steel bolts to 550 degrees Fahrenheit. They turned a pale yellow. Then two days later they darkened to a nice yellow color.

My questions are:

Why did the bolts darken?
After heating the stainless steel or chrome plated bolts, is the surface just as hard?
Can I expect that at some point the color will stop changing and then remain the same (no oxidation)?
Is there a medium (the Incas (or Aztecs) used KNO3 (saltpeter) heated to its melting point to produce a beautiful turquoise patina on steel) I should use?
How hot do I need to heat chrome plate and stainless steel to get yellow and blue?
Is there a better way to have a hard surface with a metal yellow and a blue that won't oxidize or change color?

I would be grateful for any help.

Robert M [last name deleted for privacy by Editor]
automobile repair/restoration - Tacoma, Washington


December 27, 2008

A. Wow.
Why did the bolts darken?

Most likely an oxidation reaction.

After heating the stainless steel or chrome plated bolts, is the surface just as hard?

probably not, although the underlying bolt strength shouldn't be greatly affected by that temperature.

Can I expect that at some point the color will stop changing and then remain the same (no oxidation)?

It will depend upon the grade of stainless (amount of nickel & chromium in the alloy.)

Is there a medium (the Incas (or Aztecs) used KNO3 (saltpeter) heated to its melting point to produce a beautiful turquoise patina on steel) I should use?

Since neither the Inca nor the Aztecs used iron, much less steel, I'm not sure about this information....

How hot do I need to heat chrome plate and stainless steel to get yellow and blue?

Sorry, don't know.

Is there a better way to have a hard surface with a metal yellow and a blue that won't oxidize or change color?

There is a technique for anodizing stainless--used to be a company in Colorado that used it for making signs, I do not know what the process is--but it must be out there, google is your friend.

Depending upon how "hard" the surface needs to be, you could also use titanium bolts, which can be surface colored to a dozen shades, everything except red.

This process is highly controllable since it can be done using controlled voltages--each voltage will represent a color. You can color different parts of pieces this way--even put pictures on the surfaces.

But while the surface will stand up to handling, it's likely that any burr or scratch on a wrench would scratch through the oxide. That said, it could be done in situ.

These colors are stable unless voltage or heat is applied to the surface. The oxide must be physically removed in order to start the process.

Charles M. Barnard
- Menomonie, Wisconsin



Getting "color" in stainless steel by heating

2007

Q. I am a small business that makes stainless steel belt buckles. I would like to know if there is a book, chart, or whatever, that would help me to get different colors when heating stainless. I am trying to get a red/orange color. Any help would be greatly appreciated.

Bill Bright
designer/maker belt buckles - Findlay, Ohio


2007

A. Old book on metal colouring by D.Fishlock (D.Fishlock: Metal Colouring, Teddington 1962.) can be very good source of infos.

Try next webpage www.bssa.org.uk/topics.php?article=140 -very good article on heat tinting of stainless steel. Hope it helps and good luck!

Goran Budija
- Zagreb, Croatia


2007

A. Color can be as much from if the torch was an oxidizing flame or a reducing flame. If you are using a furnace, the color will vary with the amount of oxygen present and the rate of cooling.
In short, trial and error on scrap.

James Watts
- Navarre, Florida



To minimize search efforts and to offer multiple viewpoints, we combined previously separate threads onto this page. Please forgive any resultant repetition, failures of chronological order, or what may look like readers disrespecting previous responses -- those other responses may not have been on the page at the time :-)



Heat patina stainless steel for outside use?

January 5, 2011

Q. Hi all-
I am working on a project where we are looking to use stainless steel panels as wall cladding on the side of a parking garage. We have seen some pretty cool colors come out of heating stainless steel to high temperatures. Has anyone tried this on a large scale with 4'x8' stainless steel panels? Does anyone know how colorfast the metal is after being exposed to weather (i.e., will the colors flake off, change, etc.)? Are there examples of something like this being done, maybe in outside sculpture or something similar? Thanks so much for your responses.

Shane Morrissey
architect - Missoula, Montana, USA


January 6, 2011

A. You can get anywhere from a light tan to a light blue to a dark blue by heating panes in an open air furnace. Not sure of what would be the best temp for your desires. Not many places can take a 4 x 8 sheet, but you could tack weld or pin the ends to form a cylinder that would be 4' high by less than 3' in diameter.
A "dirty" part will have stronger colors. This would take some trials to sort out what would be best. You might use 1' panels and piggy back them with someone else parts in the furnace.
The color is mostly oxides of nickel and or other elements in the alloy. It takes a harsh acid treatment to remove it on aircraft parts, so I will guess that it should be long lasting outside.

Torch work could produce some wild patterns.

James Watts
- Navarre, Florida


January 11, 2011

A. Download free booklet on coloring and plating of metals,including heat tinting of stainless steel :
attachments.wetpaintserv.us/TfuRNJ_GLYiy-a_0jvIMxA483937

Goran Budija
- Zagreb, Croatia

----
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 https://www.finishing.com/library/budija/budija.pdf.



Heat color finish on Stainless, Durability of the finish outside

April 26, 2019 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Hi there.

I am trying to figure out some information about the feasibility of torching some stainless steel to achieve a bronze/slight blue finish. It would be on an outdoor sculpture and I know I have achieved great results with a few chandeliers, and wall sconces, but those were indoors. Can it be left without a clearcoat if so?

Would acidic rain, or UV have an effect on the sculpture over time to dull or remove the heat treatment/finish.

Any feedback would be much appreciated. I tried to find any info on this already answered on the site, hope it is not a redundant question.

Chukk Bruursema
Designer/Fabricator - Asheville, North Carolina


May 2019

A. Hi Chukk. You can google for info and case studies of buildings made of colored stainless steel, and I think you will find that if the coloration is done electrochemically and done well it can be rather durable.

But my suspicion is that some, and maybe a lot, of the coloration applied by a torch is not a true change in the structure of the stainless, or even a durable translucent oxide coating, but oil residues which won't prove very permanent.

I doubt that you'll find any info in finishing or architectural journals. So, unless you can find some info in artists' magazines, I would suggest doing some scrap pieces and then trying to remove the coloration with detergent and very mild abrasives, and trying to acquire a feel for its durability. Best of luck.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Aloha -- an idea worth spreading



Is Heat-Colored 304SS more or less subject to corrosion?

February 14, 2020

Q. Hello!

I'm a just a Hobbyist who occasionally makes small pieces from 304 Stainless, including the occasional chain-maille bracelet or hanger. I only use 304: firstly so that artsy pieces have a coherent appearance among the parts; and secondly, because it's the least expensive steel that doesn't corrode under normal conditions, since I cannot at all afford to have tiny quantities of tiny parts commercially treated.

Anyway!,
So, I do really like the colors I can get from 304SS by just using my small butane torch, especially the violet!, but I don't at all know whether that sort of colorization makes the steel more subject to corrosion, or less so, or even whether it has no effect on corrosion. I've tried to search for the information, and haven't been able to come up with the answer.

Again, this is for small art projects that don't experience any unusual circumstances of environment or usage. Environmental conditions would only be normal household environments, or occasionally, birdbath parts or parts in other garden-type decor.

So, to what degree (no pun intended ha ha!) does, or doesn't, heat coloration of 304SS affect its corrosion?

Many thanks!

- Kris

Kris Krieger
Hobbyist/Artisan - Houston, Texas USA


April 19, 2020

A. Hi kris,

From what I know about titanium, these colorations that you see are due to thin film optics.

As you flame the surface, a thin (COLORLESS) oxide layer is formed, now due to the interference of light (because of this layer) it shows a color.

Different film thickness will give different colors, hence the longer you blow the torch the color changes accordingly.

Since its an oxide layer, it basically becomes heat anodizing, so it should help prevent corrosion.

regards,
vedant.

VEDANT AGGARWAL
- DELHI,INDIA


April 27, 2020

thumbs up sign Hello VEDANT

Thank you so much! Titanium thin-film optics?, that's fascinating and - dare I say it? - Cool, in my opinion ;) I do know that, in the area of non-precious jewelry, numerous items, such as hematite, are often given a Titanium coat which gives the item a "rainbow" coloration, and I *had* wondered about that as well. And yet, as a pigment, Titanium White is about the purest, brightest white available.

I remember seeing something about using *chromium* oxide thin films as nano-resistors and using the principle of interference to measure the thickness (in nm) - I just think those little intersections of info are fascinating =:D

Well, I'll stop before I go off on who knows what tangents, but anyway, Thanks again! =:D

Kris Krieger [returning]
hobbyist - Houston, Texas USA


May 7, 2020

A. Kris,
Discoloring stainless with heat is similar to the blue/brown Heat Affected Zone (HAZ) discoloration seen on either side of a weld on stainless, where the alloy reached almost-but-not-quite the melting point. The HAZ is certainly more susceptible to corrosion than the areas away from the weld; however, it can be passivated to restore the corrosion resistance. Passivation with citric acid will not remove the color.

ray kremer
Ray Kremer
Stellar Solutions, Inc.
supporting advertiser
McHenry, Illinois
stellar solutions banner


May 8, 2020

thumbs up sign Thank you for that info, Ray! It's interesting that citric acid won't remove the color. I'll look into that some more, and give it a try.

Kris Krieger [returning]
casual hobbyist - Houston, Texas USA


May 18, 2020

A. Very good article about heat tinting stainless steel:
https://www.bssa.org.uk/topics.php?article=140

According to Russian sources, electrochemical and heat-obtained colours on stainless steel can by treated in potassium dichromate solution too (5-15 minutes, 5-10% solution, 70-90 °C). Cathodic treatment in 250 gms chromic acid/ 0,75 gms sulphuric acid can be used too (increases abrasion resistance - treatment duration 20 minutes).

Abrasion resistance can be improved with diluted waterglass (according to one expired patent).

Hope it helps and good luck./p> Goran Budija
- Zagreb,Croatia



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