How to Rainbow Anodize Stainless Steel

[chrystylus]

I was wondering if anyone knew the best way/equipment to create a rainbow effect on stainless steel. I am a total beginner and haven't even purchased an anodizer yet, since I wanted to make sure I ordered the right one. I would say more workload would be about 3-5 products a day of 1/2 inch gauged stainless steel. Any recommendations would be appreciated.

[sswee]

chrystylus,
You need to investigate the material treatment you are wanting more before you go and by an anodizing kit. Anodizing is growing an oxide layer under controlled conditions to get a protective coating that can be dyed. It is done to aluminum. The only other material I am familiar with that can be anodized is titanium. I haven't seen or heard of anodizing stainless steel or an anodizer machine. Can you give an example of a part that has the finish you want or post a pic of one? It sounds like what your asking about may be a heat treatment finish.
SS

[Tim Wiltse]

The only "rainbow" I have even seen on stainless steel is from getting hot....as in stainless steel car headers. You can't anodize stainless steel.

LAter,
Tim

[alabama_lowlife]

i've seen a couple knives and zippo's that have that "discoloration" kinda look....like oil on water. is that you mean? i've been wondering how they did those.

[alabama_lowlife]

[acidrain]

Those are titanium.

[destroyer125]

Can also be done by nickel plating a part, then running a high voltage through it. Im not sure exactly how the process works though

[mcaswell]

I have some notes on anodizing titanium (found in a dusty corner of my hard drive)
Acidrain's statement that the knife is titanium would certainly give the colors shown.


I have experience with anodizing small parts in titanium (comercially pure grade 1 and
Ti 6Al 4V) and niobium, but nothing as large as your part. The current densities that
I use vary from about 5 amps per square inch to less than an amp per square inch. I
suggest that you start out on the lower range to avoid accidentally etching the piece. I use
a solution of 3-5% by weight trisodium phosphate in water. Keep the solution below 80
degrees farenheight. I get more vivid colors on the 6-4 than the cp titanium, probably
because it seems to take a higher finish easier. If you do not already have a suitable tank,
you might try anodizing the piece with a brush saturated with the solution connected to the
positive lead and the piece grounded to complete the circuit. You could use a painter's brush
with the metal ferrule wired to the lead and then insulate the handle for safety. Artists use this
technique to paint on sheets of Ti.

Ti6-4 surgical instruments are routinely anodized for color coding. The first blue color appears
around 28V. The exact relationship between color and voltage will vary with each setup.
You will have to experiment. If you are using titanium clips to hold the work, the anodized
layer on the clip will need to be removed mechanically or in a dilute (5%) HF solution
(handle with care) between each run.

Ken,

For the anodizing of titanium we use the following bath.

80 vol% phosphoric acid
10 vol% sulphuric acid
10 vol% water at room temperature.

The color of the anodic layer depends on the anodizing voltage.

Anodizing of titanium can also be done in 3 - 5 w% trisodiumphosphate.

Titanium anodizing is a unique coating which partially penetrates into the base metal,
improving fatigue strength, making it stronger and increasing its resistance to galling,
with minimal dimensional change.

With titanium in a bath of TriSodium Phosphate you get the most beautiful color of blue
imaginable. All you need to do is to immerse the part, turn on the current and voil‡ ,
bright blue. Not gray but close??

A true grey from TSP is not probable.

Brown, blue, silver, yellow, purple and green are possible at voltages up to 200. There are several different shades possible for each. Precise color requires precise voltage control. It anodizes nearly instantly. Surface prep makes a significant difference in the luster or look of the product. Does not need any further protection after anodize.

From 10% to 3% solutions are recommended.
The color red is not possible with titanium anodizing nor is black. Apparently neither exists in the spectrum created by the oxide layer formed on the surface. The color exists only as reflected light.

A bath that can be used for anodizing titanium is

phosphoric acid 80 w% Room temperature
sulphuric acid 10 w%
water 10 w%

The bath is controlled, as mentioned by James Watt, by the voltage. The voltage is critical.

I have been coloring Ti for decorative use (on a small scale ) using Coca - Cola
and stainless steel cathodes, powered from my anodising rectifier at + - 60volts .
The trick is in how long you dip it , the longer , the darker . A couple of seconds is
normally enough . It's a great party trick . By the way , the color is dependent on the lighting ,
and finish of the part , it is caused by difraction of the light waves.

Oxalic Acid, Phosphoric Acid (Coke Cola) Sulfate of Ammonium (Fertilizer), TSP
(All Purpose Cleaner)

All of the above mentioned chemicals will anodize refractory metals.

I have been anodizing refactory metals for the past 17 years and have not added
sulfuric acids to my solution. Keep it simple and friendly.


Color anodizing titanium for appearance (not functional) can be achieved in most any
sulfuric anodizing or hard anodizing bath by first cleaning the titanium in a nitric/hydrofluoric
bath (25-35% nitric with 2-4 oz/gal hydrofluoric) for about 10-30 seconds. You then anodize
the parts by slowly raising the voltage from the starting voltage. Color changes occur about
ever 2-4 VDC. Color changes occur much like octaves on a piano - as you increase voltages
the color changes will proceed thru several octave ranges. When you achieve the color you
are seeking, record the voltage and anodize subsequent lots at that voltage - no need to raise
the voltage slowly once it has been determined.If you don't like the coating, strip in the
nitric/HF bath and try again.

I use a trisodium phosphate solution (3% to 5% by weight) to anodize titanium and niobium.
This solution is quite safe and gives excellent colors in a small scale operation. The quality
of the color achieved depends on the surface finish of the part and its cleanliness, (free of
dirt and all oils). Current should be low: I use about 2 amps on small parts. The bath should
be kept below 80 degrees farenheight. If the bath is too hot or the current too strong, the part
will be etched and turn grey. The part must then be polished and anodized again. The voltage
is what determines the color. I use a range of 20 to 75 volts. If I remeber right, yellow occurs
at about 42 volts. Also, I have read that it is best to use a cathode of the same material that
you are anodizing.

Unfortunately, 1 or 2 volts makes a difference in the exact shade that you get,
so you will have to take what ever is near.

[luminous]

Originally Posted by mcaswell

I have some notes on anodizing titanium (found in a dusty corner of my hard drive)
Acidrain's statement that the knife is titanium would certainly give the colors shown.

I've not done much Ti yet, but I've anodized a bit of Niobium for the wifes jewelry projects. The colors range is quite similar to Ti.

I use a solution of about 5 grams of Borax in a quart of water. Almost anything that makes the water conductive, but doesn't harm the metal will do the job. No acids or nasty chemicals required.

Here's a Nb color sample I made earlier this year that shows Color Vs. Volts for niobium

http://www.weirdstuffwemake.com/weir...or_samples.jpg

Steve

[alabama_lowlife]

so can aluminum be anodized to look like that? i have absolutely no understanding of what was said there....it looks like french to me. i don;'t intend to try, but i was wondering if a valve cover or something could be done like that.