Various colors were formed on the mechanically polished 304 steel surfaces via the low-cost and fast nanosecond pulse laser coloration route. A typical radiation time is around 1 minute to color each square with an area of 5 × 5 mm2. Different colors were reached via semi-empirically varying laser scanning speed, repetition rate, and pulse width. The relations between nanosecond laser parameters and final surface performance have been discussed elsewhere12,13,14,15, yet out of the main focus of the present work.
Color information of the laser markings was obtained through polarized light microscope without filters. During the measurements, the incident white light beam was kept perpendicular to the sample surface. As shown in Fig. 1, three colorized samples were prepared, displaying straw-yellow, cornflower-blue and fuchsia colors, respectively. The insets were taken by digital camera with tilted directions (raw photo shown in Supplementary Fig. 1), appearing slightly different colors. To quantitatively describe color information, the commonly used RGB color model is presented here. The RGB model is built following the way in which cone cells in human retina perceive red, green and blue colors16, and all the three color components vary from 0 ~ 255. A larger component value indicates a higher brightness and saturation. In order to get the average RGB values of each photo, the red, green and blue values of each pixel were counted and averaged. Table 1 indeed shows that all the generated colors have relatively low RGB values, or in other words, colors are not fully saturated.
Figure 1Optical microscopy images of the colorized surface. (a) Sample 1, straw-yellow, (b) Sample 2, cornflower-blue, (c) Sample 3, fuchsia. Photos of insets were taken by digital camera.
Full size image
Table 1 Color information of the laser markings.Full size table
Optical reflectance was measured at the incident angle of 30° and 70°, respectively. With Xenon lamp as the light source, the incident light spectrum agreed well with the solar spectrum in the visible light range17. In both Fig. 2a and b, low reflectance values were recorded, yet it is noteworthy that the reflectance increased slightly with the incident angles. This is the characteristic behavior of structural color effect. In general, the presented colors vary in a limited scope. Differences between Fig. 1a~c and the insets suggest a weak influence on the final colors from the aspect of light-matter scattering. Among the three samples, sample 1 exhibits the highest reflectance. Meanwhile, a rise of ~20% in the reflectance indicates that sample 1 is more influenced by the structure color. For each sample, the reflectance roughly increases along with the light wavelength, in accordance with results in previous research18.
Figure 2Optical reflectance property measured with incident angles of: (a) 30°, (b) 70°.
Full size image
To clarify the light-matter interaction, it is essential to acquire the information of morphology and thickness of the laser-induced layer on steel surface. Sample morphologies depicted in Fig. 3a–c show that the surfaces are basically composed of irregular micro-wrinkles with lateral dimensions in 10 µm scale, much larger than the wavelength of visible light. Thus, possibility of light interference with the microstructure is rather low19. Although sample 1 and 2 show distinct colors, their microstructures are quite similar except that the wrinkles in sample 1 are larger and arranged more sparsely. Short-order periodic grooves appear in sample 2 (Fig. 3b), but their influence on the coloration can be still neglected due to the lack of quantity. In Fig. 3c, there are uniformly arranged gratings. However, the periodic length is around 8 ~ 12 µm, far from the coherent length to interfere with visible light. Therefore, the structural color effect may only originate from the light interference with the laser-generated film.
Figure 3Morphologies of laser marking and the simulation results of reflectance. (a)~(c) SEM images of sample 1~3, respectively. (d) Simulation results of optical reflectance.
Full size image
The film on top of steel surface was formed during laser treatment, and its thickness can be estimated through surface profile measurements. The layer thickness of sample 2 is ~300 nm, while the other two are approximately 800 nm (Supplementary Fig. 2). As an alternative non-destructive technique, ellipsometry method20 was also employed to double-check the thickness. For sample 2, the ellipsometry method gave the thickness of 314.4 ± 37.6 nm (Supplementary Fig. 3), which is very close to the surface profiler result (300 nm). However, such a method could not be accomplished for sample 1 and sample 3, even with the AutoRetarder which allows depolarization for surface of certain roughness. It might be due to rather high roughness and limited region of the laser induced films, which are beyond the applicability of the surface-sensitive ellipsometry method21. In this case, we carried out cross-sectional scanning electron microscope (SEM) measurement in order to directly obtain the film thicknesses (Supplementary Fig. 4). Values of 764.1 ± 31.7 nm, 338.1 ± 20.9 nm and 807.6 ± 54.2 nm were found for sample 1–3, respectively, in good agreement with the optical profilometer results.
Simulation work was carried out to evaluate the reflective ability coming from thin-film interference. Smooth film models were built, and the morphology information on the surface was discarded. The layer thickness was set according to the surface profile results, while incident light set perpendicularly. The refractive indices and extinction coefficients were set based on ellipsometry measurement results. The simulated results in Fig. 3d have the same trend of wavelength dependence as the experimental determinations in Fig. 2. However, discrepancies of ~10% have been found between the calculated and measured reflectance for sample 2 and sample 3. This can be attributed to typical simplifications of theoretical models and homogeneity of materials employed in the simulations22, 23. Indeed, even for a surface composed of single element (e.g., bare silicon surface), theoretical results22 can still vary more than 10% against experimental ones24. In spite of the discrepancies, no obvious peaks can be observed in the reflectance curves. Thus, structural coloration does not dominate final colors on the nanosecond laser marked surfaces.
Quantitative analysis of surface compositions is the prerequisite to evaluate the composition based coloration mechanism. By the energy dispersive spectroscopy (EDS), we roughly examined the elemental information of the samples. Fe, Cr, Ni and Mn were the primary elements, and more Cr was detected in sample 1 (see Supplementary Table 1). Since the detection depth of EDS (~1 µm)25 is much larger than the film thickness, EDS result was mixed up with elemental information coming from substrates, making it inappropriate to analyze the thin films on the surface.
XPS is a surface sensitive technique and thus available to focus on the thin markings. Figure 4 shows the XPS spectra of Cr 2p, Fe 2p and the details of peak fitting are listed in Supplementary Table 2. For Cr 2p spectra, two groups of peaks were identified in Fig. 4a, which were Cr2O3 at ~576.5 eV and a spinel structure at ~575.4 eV, respectively26, 27. The typical spinel structure is XY2O4, where X and Y represent ions in +2 and +3 valence28. In this work, its form can be specified as (Mn2+ x1Ni2+ x2Fe2+ x3)(Fe3+ x4Cr3+ x5)O4, where x1 + x2 + x3 = 1 and x4 + x5 = 2. In contrast, the spinel peaks disappeared on the spectra of steel substrates, and chromium of metal form was detected (Supplementary Fig. 5). Similar results are also found in Fig. 4b. The spinel compound and Fe2O3 were identified. As a typical feature for Fe 2p spectra of stainless steel, the pair of satellite peaks of spinel compound were also specified. It suggests that the spinel structure was formed during the laser treatment process.
Figure 4XPS spectra of: (a) Cr 2p, (b) Fe 2p. In each panel, the spectra of the three samples are illustrated. Each pair of doublet peaks were illustrated with identical color. The scatter plots are experimental results, while the magenta and grey lines represent the fitting envelopes and backgrounds, respectively.
Full size image
Indeed, native passivation layer on stainless steel surface is mainly composed of Cr2O3, Fe3O4 and Fe2O3 29. Alloy elements were promoted to disperse from the substrate to the passivation layer due to the heat effect of pulsed laser, and they could be more easily oxidized by oxygen. Oxygen partial pressure was therefore reduced, producing a reductive atmosphere in local region. In this case, Cr and Mn have the priority to react with the remaining oxygen and form their metal oxides. After that Fe was also oxidized to FeO, meanwhile, laser beam moved away and the temperature as well as the reaction rate dropped consequently. Oxygen partial pressure rose, which facilitated the simultaneous oxidization of Fe, Ni and the metal oxides. The spinel compound was then formed. It was also possible for Cr3+ substituted by Fe3+, making the spinel structure even more complicated30.
It is noteworthy that very small amount of Ni was detected although there was 8~11% in the commercial 304 steel substrate (see Supplementary Table 2 and Supplementary Fig. 6). Ni is nearly absent in the native passivation layer, while that in the substrate usually completely dissolved in γ–Fe, making it difficult to escape31. The EDS results indicated more than 6% of Ni, most of which should come from the substrates.
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Q. Hello,
I am Etching colors onto stainless steel Art Panels.
I'm using [ed. note: supplier's name deleted at their request], etc., products. Are there solutions available to induce various colors onto the stainless steel surface. I have used heat to effect colors and appreciate any guidance. Thank you. JM
John Mohrlein
- Chicago Illinois
A. Hi John. Coloring of stainless steel is usually not done with dyes or pigments so there isn't one solution for red, another for blue, a third for green or anything like that. Rather, different thickness of the oxide coating give different colors, although PVD coatings and electrophoretic lacquer are also sometimes used.
We have hundreds of postings about coloring of stainless steel in this forum, not only on this thread, but topic 16927, topic 1039, topic 21437, topic 24520, etc. Please do a quick scan then follow up with your next question.
Luck & Regards,
Ted Mooney
, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
⇩ Closely related postings, oldest first ⇩
Q. Do you know how to produce interference colours over austenitic stainless steel by means of anodization (chemical oxidation)?
Thank You!
kobi shterenberg
Israel
A. I believe International Nickel Corp. has a patent for coloring austenitic stainless steel using an electrical/chemical process.
Paul Vernon
Q. Yes I was just curious as to how can I anodize stainless steel. People have told me that it is impossible but I was wondering if it is after seeing your title. I am in the Paintball industry and one of the guns that are made are called AutoMags; the body of this gun is stainless steel. I would like to anodize it any color to show and sell. If you have any info on these I would appreciate it greatly. Thank you for your help.
Nathaniel Pickles
paintball
A. My company Prismatic Stainless Steel colors stainless with the INCO process. The colors available on 304 S/S are champagne, Bronze, Blue, Gold, Red/Green and black.
adv.
If you need further information, please feel free to e-mail me.
Regards,
Bob Bramson
B&M Finishers / Prismatic Stainless Steel
Kenilworth, New Jersey
Multiple threads were merged: please forgive repetition, chronology errors, or disrespect towards other postings [they weren't on the same page] :-)
Q. I have a customer that wants my company to mark or color some stainless steel hardware red. I have checked with the local plating companies that we use and they all laughed and said to offer paint as a substitute. Are there any dyes or other permanent marking materials/methods available?
Thanks.
Ed Morbitzer
- Garland, Texas
A. Permanent markings can be made using laser engraving. I've seen it done on SS license plate frames and surgical instruments. Check under engravers in the yellow pages.
Good luck!
Michael Liu Taylor
specialty stainless steel distributor - Dallas, Texas
A. International Nickel Co has processes for coloring stainless steel. Or Contact the Nickel Development Institute for information on coloring SS.
Don Baudrand
Consultant - Poulsbo, Washington
[on Amazon or AbeBooks affil links]
[on Amazon or eBay or AbeBooks affil links])
(Don is co-author ofand
Multiple threads were merged: please forgive repetition, chronology errors, or disrespect towards other postings [they weren't on the same page] :-)
Q. A company in Japan describes their process for coloring stainless. "The surface of stainless steel is covered by a thin transparent film of metal oxide. When the thickness of the film is changed by P/10 to P/100 microns, the surface of the stainless steel can be seen beautifully with colors formed by the interference phenomenon of light. Using this process, various colors can be formed without painting or coloring. Depending on the viewing angle, the color changes slightly in appearance that cannot be obtained from any other process." What is this called and how might I locate a company in the US that colors patterns on stainless steel? (They reproduce artwork, not just solid color.) Is this different than anodizing aluminum? Any direction would be great, even getting the terminology right would be productive!
Thanks,
Erin Caruth
- Ithaca, New York
A. Hi, Erin. Yes, anodizing of stainless steel is analogous to the anodizing of aluminum from the standpoint that the components are immersed in a solution and the electricity causes the formation of an oxide coating. But they are very different in terms of the coloration. You have described the situation for stainless steel, but anodized coatings on aluminum are much thicker and the color does not come from diffraction effects but from dye. You can learn more about anodizing of stainless steel from B&M Finishers / Prismatic Stainless Steel [a finishing.com supporting advertiser]. Good luck.
Regards,
Ted Mooney
, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Q. I am trying to finish wind chimes that I make out of stainless steel (for longevity). I am bored with the brushed and polished looks. Want to try coloring the steel. Is there a process I can do that would be similar to parkerizing, or anodizing(like Al). Any help would be appreciated.
P.S. paint gets chipped off, too much upkeep.
Alan Mason
hobbyist - Kannapolis, North Carolina, United States
A. You can try heat coloring them ... just use a torch with a clean flame to heat them up. The colors are limited but nice in my opinion.. You can get browns, copper, near gold, yellowish, purple, light blue, blue, etc. I don't know how in depth you get with the tone of the chimes but heating it may change the tone a bit. I think I also recall an advertiser on this website offering steel coloring services. Might look into that
Jason Aube
- Flint, Michigan
Q. Dear Sir,
We want to know the exact process for stainless steel colouring (Chocolate brown) We have tried the process in the following manner but not succeeded.
1) D/c rectifier used
2) volt : 1-2
3) Current : 6Amp / dm2
4) Mixture : 2.5M CrO3 + 5M H2SO4 of aqueous solution
5) Time : 5 Minutes
6) Anode : Job
7) Cathode : Lead Plate
Kindly give the exact process.
P. GANESAN
Electroplating - Chennai, Tamil Nadu, India
Q. I'm interested in producing electrochemically coloured stainless steel and would like to find out more about the process used.
Clifford van Lelyveld
Private enquiry - Johannesburg, Gauteng, South Africa
Q. Hello everyone,
I'm a designer for a watchmaking company in Paris. I don't have any in depth chemical or physical knowledge.
We are interested in coloring stainless steel watch cases. So far we have used PVD but although it is excellent quality process (it lasts long) we have just a limited choice for colors: gold, pink gold, black, gun black, blue...
We are trying lacquer on stainless steel but it comes off very easily after a while. Can anyone can give me some up-to-date on what treatment would be suitable if I want to color steel in a fairly wide range of color? Thanks a lot for your help.
Best regards.
David A
[last name deleted for privacy by Editor]
watchmaking - PARIS, FRANCE
A. An additional alternative might be anodic coloring. B&M Finishers offers the Prismatic process for stainless steel. Good luck.
Ted Mooney
, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Q. I am having some difficulty in locating information to plating Stainless Steel Screws to achieve a Weathered Brass Finish. We may also go to a Natural Brass Finish as well. Is there any source I can contact or any information any one can give on plating Stainless Steel Screws?
Rob Siedschlag
Outdoor Brass & Copper Lighting Fixture Manufacturer - Escondido, California, United States
A. Several different technologies are available. First, the screws can be brass plated; this is similar to plating onto steel screws except that a different preplate cycle is required, which includes a nickel strike to activate the substrate. A second possibility is color anodization of the stainless steel. Third, a brass colored translucent electrophoretic lacquer can be applied to the screws.
Ted Mooney
, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Multiple threads were merged: please forgive repetition, chronology errors, or disrespect towards other postings [they weren't on the same page] :-)
"Metal Colouring"
David Fishlock
on
AbeBooks
or
Amazon
(affil links)
Q. How can stainless steel be coloured? Please let me know the availability of the book "Metal Colouring" by David Fishlock. Thank you. C
C.K.RAVEENDHRAN
metal finishing - COIMBATORE, TN, India
A. Try Abebooks website!
Goran Budija
- Cerovski vrh Croatia
A. Stainless steel can be colored via an INCO anodization process but, as far as I know, this is still proprietary. B&M Finishers is one supplier of the coloring services for stainless steel.
Ted Mooney
, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
A. Stainless steel usually don't change any color. However, if the surface plating is broken, I think it is out of control at that time, but may plating it again.
Frank Zhao
- Taicang, Jiangsu, China
Multiple threads were merged: please forgive repetition, chronology errors, or disrespect towards other postings [they weren't on the same page] :-)
Q. We manufacture an industrial type of lock and key that is machined from 316 stainless steel and then the items are electropolished. The key is a bulkier style key than your standard house or car key. We are trying to figure out a way to color code the keys. Since the lock is comprised of 316 stainlees steel, is there a chemical process to color coat the steel? Plastic slip-ons or dipping is not an option since the key can be placed in high heat areas. We need red, yellow, green, and blue.
Sean T McGuinness
Kirk Key Interlock Company - Ohio
You can use next anodic process(proprietary processes also exists):
sulfuric acid(1,24).......1 lit
potassium dichromate........7,5 gr
temp........................7o-95 C
0,06 A/dm2, 1,3V lead cathode
only for 18/8 SS!
Good luck!
Goran Budija
- Cerovski vrh Croatia
Multiple threads were merged: please forgive repetition, chronology errors, or disrespect towards other postings [they weren't on the same page] :-)
Q. I would like to find out are there any mistake with my setup , I had made up a 10 litre (concentrated) H2SO4 bath adding 75 grms of sodium dichromate into it , plating my stainless steel (304) panel size 3 by 5 inch , heating the solution up to 75 degree c , using lead as cathode . plate it for about 30 mins at 5 to 7 v but there is not any colour effect , instead the surface of my panel became like tarnish and had flow marks which I do not know what is that ... Can any one please advise me what should I do ..?
Roy Choon
plating shop - China
I need advise how could I get colour on stainless steel , I need some colouring on stainless steel(304) panels size 3 by 5 inches , reading some articles from here eg. thread No. 33236 I actually try out the method posted here by me. I am expecting blue or black colour on SS(304)panels ....
Roy Choon
[returning]
plating - China
Fishlock in his book on metal colouring gives somewhat different formula than Dettner/Elzes Handbook:
sulfuric acid 250 ml/lit water
sodium dichromate 60 gr/lit
70-95 °C, anodic current 0,6 A/sq.ft
Colour sequence: brown, blue bronze, reddish brown, deep purple to green (45 minutes time). Lead anode. Only for 18/8 steel.
Hope it helps!
Goran Budija
- Cerovski vrh Croatia
Q. Dear Sir,
I want to find out how can I make Stainless steel coloring without electrical power. If you know some way to do so please send my these ways or you can guide me to some place to find some books or some researches in this matter.
Best regards,
Mohamed Kamel
E-Med - Cairo, Egypt
A. Stainless steel can be black oxided, Mohamed. If black would satisfy you, please search this site for "black oxide stainless". Good luck.
Ted Mooney
, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Q. I would like to add color to stainless steel faces that I am creating. Have seen various artists at art shows who are coloring their stainless steel in vibrant shades - virtually every color conceivable. You can almost still see the metal through the color.
Can you help me figure out the technique?
Thank you.
Kelly Stacy
Artist - Gainesville, Florida, USA
A. What you are seeing are the use of automotive transparent lacquers. Most likely, you can check out any auto big box store and in the can section. There will be a number of colors and brands: VHT is one.
You also can go to Eastwood's site. They are an auto hobbyist supplier with an info laden site about their products. The item is then top coated with a clear.
You also can use a transparent colored powder coat.
I tested some of the Harbor Freight's colored sockets and wrenches they started selling. First by soaking in lacquer thinner [on
eBay or
Amazon], after 50 minutes the clear started to bubble up and off the socket. Then the color would transfer to the rag.
I also did some scratch test with auto sanding papers, files and a piece of square steel stock for a nick test. They all damaged the surface finish readily.
You can go to this thread to see the pictures of the sockets and tests. At Sculpture.com it is in the sculpture news and events forum.
It is a somewhat fragile coating, as it nicks and scratches quite easily. The powder coating would be a tougher finish.
Glen Perye
metal fabricator/artist - Mount Clemens, Michigan
Q. Do you know of any finish that can be done, other than paint, to 18-8 stainless steel that is the color red?
JOHN A BECKER
JOB SHOP - COLUMBIA, NJ
A. Stainless steel can be anodized to red colour. You can use proprietary process or you can make your own solution.Try uspto .gov website -there you can find some expired patents on colouring of SS.Hope it helps and good luck!
Goran Budija
- Cerovski vrh Croatia
Multiple threads were merged: please forgive repetition, chronology errors, or disrespect towards other postings [they weren't on the same page] :-)
Q. I have a client that is interested in coloring stainless steel door hinges. I know there is a method that will produce a gold finish when heated in a controlled atmosphere.
I am looking for temperatures, times, and atmospheric gasses.
Ralph Dixon
Decorative Plating Consultant - East Berlin, Pennsylvania
A. Good afternoon:
My guess is you will end up running trials to find the color match you're looking for. Once you find a color match, keep using the same stainless grade and processing parameters. The British Stainless Steel Association has a webpage that discusses this subject:
www.bssa.org.uk/topics.php?article=140
Steve Bizub
- St Louis, Missouri
A. PVD coating on stainless steel is the answer. TiN will coat these parts. You might want to consult www.svc.org and check with them regarding it. Good luck.
Michael Liu Taylor
specialty stainless steel distributor - Dallas, Texas
Q. I am currently exploring 304 Stainless Steel, which I forge in my studio. In order to get the best finish possible I am sending it away for electropolishing. Does anyone have advice on coloring electropolished steel?
I primarily need to color parts black for contrast, similar to bluing or heat darkening steel.
Would heat darkening electropolished steel ruin the protection it offers? (I've read that bluing solutions simply do not work on stainless steel)
Is there a homemade chemical process I can use?
If painting is the only solution, must I rough up the surface for it to hold properly and, if so, will roughing it up with sandpaper ruin the electropolished surface?
Thanks!!
Ken Rowe
Sculptor - Fort Myers, Florida
A. Try next download free booklet on metals coloring:
attachments.wetpaintserv.us/ZLSnLKosv0l3CnE9hGDi7w488720
There you can find small chapter on stainless steel coloring (by heat, chemically, electrochemically). Hope it helps and good luck!
Goran Budija
- Cerovski vrh Croatia
Ed. note Jan 2017: Although wetpaintserv.us was a legitimate site when Goran posted this, it is currently 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.
A. There are formulations of "bluing" solutions that will work on stainless steel. I have used them on products that are exposed to the elements (planters etc) without issue. They contain nitric acid, though and so will etch the surface and you will loose any glossiness you might have obtained by electropolishing.
EPI / Electrochemical Products Inc. [a finishing.com supporting advertiser] makes a product called Instablak 333. You may want to consider shopping it out, as it takes a bit of practice to get an attractive result.
Regards,
Justin Kumpf
- Philadelphia, Pennsylvania, USA
Q. I am interested in D-I-Y finishing options for stainless steel.
I'm particularly impressed by using electrochemical anodizing processes on titanium in combination with masking techniques to create things such as this:
Over the course of the last week I have been reading a lot about processes to colour stainless steels, the INCO method and its successor.
"Stainless Steels: An Introduction and Their Recent Developments"
on
from AbeBooks
or
Amazon
(affil links)
I found a very interesting ebook (Stainless Steels: An Introduction and Their Recent Developments.
detailing processes. I've since found out that heat colouring might hurt hardened steel and the oxidization process alters the steel composition below the oxide layer. But electrochemical colouring does not have these drawbacks if I understand correctly and by using masking agents one can effectively create patterns/shapes/forms when using electrochemical colouring process. This can't be done using heat colouring approaches, correct?
I'm no chemist and english is my second language, so I've come here to ask if I have options as a hobbyist to colour stainless steel through electrochemical process. I am worried for example the chemicals used aren't over the counter available. Like the online readily available anodizing solutions for titanium and aluminum. It's important to me it is a do it yourself option.
Jan Jansen
Hobbyist - Groningen, The Netherlands
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Ed. note: Additional threads about coloring/anodizing of stainless steel include topics 16927, 21437, and 24520