"Rainbowing" and "Bluing" method for Stainless Steel

A. Various colors on stainless steel 18 Cr / 8 Ni)

7,5 grams of sodium dichromate, 1000 ml of sulfuric acid (1,24 g/cm3), lead cathodes, object as an anode, 70-90 °C temp., 0,06 A/dm2, voltage 1,3 V - colors depend on the duration of the procedure (5-50 min.), brown, blue, reddish brown, yellow, green.

According to Russian literature after processing items should be soaked in a solution of potassium bichromate (5-10%), 5-15 minutes, 70-90 °C temperature of the solution. According to one Chinese patent treated objects can be then immersed in a hot diluted sodium silicate solution (1-5%, 95 °C, 3-10 min. ). Hexavalent chromates are carcinogenic and toxic, molybdate-based solutions are now being proposed as a substitute.

According to Wikipedia article on Chemical coloring of metals. Hope it helps and good luck

A. Immersion in boiling solution of 950-995 ml water and 5-50 ml phosphoric acid ⇦this on eBay or Amazon [affil links] can be used too (according to USPT 2,521,580). 180 minutes! Hope it helps and good luck!

A. You must test that process, if 100 °C = 180 minute, maybe at 50 °C = 360 minutes and at 25 °C = 720 minutes...

I think that you can try ex USSR patent SU 815081 too: 100 g sodium thiosulphate ⇦this on eBay or Amazon [affil links] , 10 g lead acetate, 12 g potassium sodium tartrate ⇦this on eBay or Amazon [affil links] , 12 g copper sulfate ⇦this on eBay or Amazon [affil links] , 1 lit water, 18-22 °C temperature of solution, 5-50 minutes, yellow, brown, red, green, blue, violet. Object must be in contact with piece of copper 300 times smaller surface than surface of treated object. Hope it helps and good luck!

A. Hi Pradeep.
In addition to this page, please see:
thread 1383, and thread 16927, and thread 24520
for lots of info about anodizing/coloring of stainless steel. Good luck!
Regards,


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

A. Hi Mr. Gopalan. I am a graduate student of Shiraz University. Me & my friend work on coloring of stainless steel. Before us, another graduate student of Shiraz University worked on this. She could give green, blue, black, brown and ... color on stainless steel. I can give you any information we have, if you give us any information you have about this.
WITH THE BEST REGARDS,

Ed. note -- Ali, Pradeep:
This forum is for public sharing of whatever people are willing to share; unfortunately, private hook-ups disenfranchise the other readers who were following the discussion with curiosity, and then were disinvited; so this forum doesn't assist with that. Apologies :-)

A. Hi Musdinoviria,
Responders can continue to describe the process & chemicals for electrolytic coloring (anodizing) for you, but other readers should not infer from this that electrolytic coloring is the only coloring option for stainless steel :-)

Stainless steel can also be black oxided (contact Birchwood Technologies [a finishing.com supporting advertiser] or EPI / Electrochemical Products Inc. [a finishing.com supporting advertiser]), PVD coated in various materials & colors, coated with titanium rainbow interference coatings, heated & oil quenched, or colored with dyes (try colored permanent markers ⇦this on eBay or Amazon [affil links] .

It may often be best to start such questions with what kind of items you want to colorize and why, what level of durability is required, and what environment they will be seeing.

Luck & Regards,


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

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

H2SO4........ 1 lit
Na2Cr2O7...... 7,5 gm
70-95 °C,
0,06 A/dm2,
1,3V,
object = anode, cathode = lead

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

A. You must use 1,24 g/cm3 (density) sulfuric acid! Today I think that alkaline process is a better solution, and it is RoHS-compliant:

NaOH.....700 gm
KMnO4....10 gm
Na2S.....1 gm
H2O......1 lit
temperature 110-120 °C
20 V

Colour sequence: brown (3 minutes) - purple (40 minutes) - black (60 minutes)
According to Dettner/Elze: Handbuch der Galvanotechnik [occasionally avail. from eBay, AbeBooks, or Amazon affil links]

A. I haven't heard of "blue ion plating" either, but it probably means a PVD-applied (physical vapor deposition) hard coating on the stainless steel of a blue color. I think if you look for job shops that offer PVD coatings they will be familiar with what you need. Or, if your needs are big enough to afford a multi-million dollar machine to do the processing in-house, the manufacturers of PVD machines will be familiar with this.

As a note to other readers interested in coloration of stainless steel, PVD processes are only applicable to high volume items because the owner/operators of these multi-million dollar high vacuum machines are concerned with potential costly contamination from a onesy-twosy order, and they also can't afford to cycle a machine nearly empty that was designed for handling hundreds or thousands of parts per cycle.

Regards, and good luck.

A. Hello Ed,
Black oxiding (bluing) of stainless steel is done industrially in a fashion very similar to black oxiding of steel, but with modified proprietary chemistry such as offered by Birchwood Technologies [a finishing.com supporting advertiser] or EPI / Electrochemical Products Inc. [a finishing.com supporting advertiser]. If you know how to do black oxiding you could experiment on the stainless. Note that hot black oxiding can be very dangerous because it often involves strong caustic solutions at 270+ °F. When water is added to make good the evaporation losses from the boiling hoy solution, there is great potential for the solution to virtually explode because water flashes to steam above 212 °C.

Rainbow coloring of stainless steel can be done by a proprietary process called Prismatic Stainless Steel [from B&M Finishers, a finishing.com supporting advertiser] and perhaps other processes
However, titanium is better for brilliant clear colors, and the pocket knives you saw probably had titanium applied to the stainless steel in a PVD vacuum chamber. A hobbyist will be able to experiment with some stainless steel coloring processes but will not be able to afford and install a vacuum chamber for the PVD application of titanium.

Although titanium and aluminum can also be anodized, the processes are very different. The coloring in titanium and stainless steel anodizing is due to the formation of thin refractive films (like the rainbow from oil on a puddle), but colors are applied to aluminum by anodizing and then filling the millions of microscopic drill holes in the anodized film with dyes.

A. Hello Jain,
Black oxide / bluing is just a coating of black rust millionths of an inch thick and would be inappropriate for an application requiring washing and scrubbing. The above-mentioned Prismatic anodizing might be appropriate though, as well as various other coloring and PVD processes. Good luck.

? Are you sure they're stainless? While it is fairly common for hobbyists to anodize aluminum, I don't know of hobbyists anodizing stainless steel. I do know of proprietary processes for anodizing stainless steel though, but I believe that green is a difficult color to get from interference coloring.

A. Yes you can

SS colour anodizing (only for 18/8 SS):
1 lit sulfuric acid
7,5 gm sodium bichromate
object=anode, cathode= lead
70-95 °C temp.,0,06 A/dm2, 1,3 V
Colour sequence brown - blue - yellow - reddish brown - purple - green.

----- I take no credit for this info I got it off another post on this site -------

! Thanks, Craig; this in turn came from Dettner & Elze: "Handbuch der Galvanotechnik" [occasionally avail. from eBay, AbeBooks, or Amazon affil links]. But hobbyists should note that sodium bichromate (sodium dichromate) is concentrated hexavalent chromium -- the toxic and carcinogenic material that made Erin Brockovich [adv: DVD on eBay & Amazon affil links] a household name; we don't know what cautions if any are included in that handbook.

Goran is exceptionally knowledgable and always very helpful; but note that he is an accomplished professional metals conservator, and trying to do your own home-brew like he is able to do may not be for everyone. For those who may be looking for a commercially available process for coloring stainless steel, from a shop with long experience in it, you can try finishing.com's supporting advertiser B&M Finishers / Prismatic Stainless Steel [a finishing.com supporting advertiser] [Kenilworth, NJ]; they call the process "Prismatic Finishing". Good luck.

Regards,

A. Hi, Luck.

We've now combined several threads including one where Goran Budija notes that the H2SO4 is 1.24 gr/cm3, i.e., about 28% (about the strength of battery acid ⇦this on eBay or Amazon [affil links] ).

Regards,

A. Hi, Rog. Sorry, anodizing of aluminum and your other processes must be done before assembly unless you are capable of meticulous and robust masking.

A. Hi Younas.
This is most likely done via PVD processing as previously described on this page. Search for "blue ion plating"
Luck & Regards,


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

A. It's pretty common to coat stainless steel screws with titanium nitride to get the gold color. Cathodic arc deposition works best. You get the best adhesion with the arc and superior part coverage. The coating is thin enough that it will not affect the screws' performance, and in most cases it will improve it.

A. Jerry,

We have not paid much attention to this technology for a long time, since the most obvious way to color stainless steel is to use hazardous chemicals. However due to massive requests to find the bio-acceptable electrolytes and eco-friendly process to color-code medical stainless steel surgical instruments, we have decided to dedicate some time to research and experiments. See attached pics - our results.

adv.
Contact us for more information.

    

A. Probably the simplest way is just to use heat. It takes a bit of practice, but small objects can be heat colored with a simple propane torch. Larger objects can be run through an oven. It is most important to ensure that the surface is clean.

I hope this helps.

Hi John. Please send us a photo of the stainless steel logo when you finish it. Paint is the most obvious solution. Any idea how you are going to achieve white and gold, other than with paint? (I don't see gold in the fabric logo).

Regards,

Platers Tape

on eBay or

Amazon

(affil links)

A. Hi Jeff. I think you might find splash anodizing of aluminum or rainbow anodizing of titanium easier than anodizing stainless steel. But with any of the materials the first step is to mask what you don't want colored. If you don't want to get involved in photomasking and special materials, you can probably cover the whole surface with platers' tape ⇨
(possibly even electricians tape), and cut out your celtic symbol with an Exacto knife ⇦this on eBay or Amazon [affil links] , then experiment with formulas and procedures as described by Goran and others.

Gradually taking the tape off the patterned area so you get different immersion times and depths should offer some color variation. But it's best to spend time experimenting with scrap before doing the actual piece.

Regards,

A. Hello!
Regarding colorizing a pattern on stainless steel, I'm wondering whether "Firescoff" ⇦this on eBay or Amazon [affil links] , or something similar, might work if the areas not to be colorized were coated, and the areas to be colored heated with a small torch?

Since such coatings are used to protect areas of a work (including even gemstones, I think) from heat damage, it seems reasonable. I don't know whether any are sprays that could be used with a stencil, or whether they'd need to be painted on (especially if thick layers are needed). But it might be worth a look?

I hope that helps!

A. Hi Kris. The phrase "heat-treat" is usually reserved for heating processes which make a material harder, so you might run into some confusion because people will tell you that type 304SS cannot be heat treated. I would think that passivating the stainless steel with citric acid is the best approach and is something that you can do with materials on hand.

I've never worked with lace but I'd suspect that oils from extensive handling with your hands would discolor them and wonder if the thing to do might not be to wear thin latex gloves ⇦this on eBay or Amazon [affil links] rather than trying to make the stainless steel impervious to hand oils?

Regards,