Anodizing Titanium Alloys to Gold Color

A. I have seen these beautiful objects, and perhaps there are several solutions that can be used. Do you have the facilities to run some tests

A. I have heard that the color changes with the voltage rather than the amperage. The exact alloy will very probably make a large difference in the exact voltage. Try 10-15% sulfuric.

A. A bath that can be used for anodizing titanium is:

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

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

Good luck.

A. 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 ± 60 volts . 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 diffraction of the light waves.

A. Oxalic Acid, Phosphoric Acid (Coke Cola) sulphate of Ammonium (Fertilizer), TSP (trisodium phosphate ⇦ this on eBay or Amazon [affil links] )

All of the above mentioned chemicals will anodize refractory metals.

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

A. 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. Good luck.

A. Robert,

I use a trisodium phosphate ⇦ this on eBay or Amazon [affil links] 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 °F. 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 remember 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.

A. Keep adding batteries in series until you get a goldish color. From a test piece on 0 to 200 volts, gold is near the middle. 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. As the batteries age, you will not get the exact color that you once did.

A. Dear Mr. Tse: I don't know whether titanium or stainless is a better spring material for you, although stainless steel seems much more common. Either can be effectively colorized, but I don't think that the typical decorative anodizing processes will give you consistent homogeneous gold or black. They are not among the typical diffraction (rainbow) colors; and while there are proprietary processes for obtaining it in both titanium and stainless, I personally don't know of any generic way.

A. Hi, Guillermo. I personally haven't heard the term "hard anodizing" applied to titanium. But what you are calling "hard anodizing", I have heard called "alkaline anodizing". It is described in specification AMS 2488, which will give you some good information about the process. The exact conditions for good anodizing seem to be held as trade secret, so it is hard to find hints in print. If you search the site for "alkaline anodizing of titanium" or "Tiodize" (which is a company famous for this process), however, you will find many threads from which you can glean some info. Good luck.

Regards,

A. If the objects are titanium then you can anodize at 24 - 30 v,10 % phosphoric acid electrolyte (or any other electrolyte, even Coca-cola can be used). If objects are low alloyed steel then you can heat them to 300 ° C (with hot air gun). If objects are stainless steel then you can anodize them in potassium dichromate/sulfuric acid electrolyte. Good source of infos can be next download free booklet: attachments.wetpaintserv.us/ZLSnLKosv0l3CnE9hGDi7w488720

Hope it helps and good luck!

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. The item on the picture is a folding pocket knife handmade by Warren Thomas. If I'm not mistaken, it is made of a layered compound of titanium and other metals, called "Timascus" for its similarity to Damascus layered steel.

So, that effect you see is not achieved through anodization alone - the purple-violet shade is anodized titanium, but the ripples and swirls on the surface are in fact the edges of layers made of other metals. That effect is also known as "mokume" or "mokume gane".

That knife also has carbide on the edge of the blade to make it harder and longer-lasting.

----
Ed. note: Thanks for the terrific explanation, David. Thanks also for sourcing the picture so we can credit it (the pic was on a photo sharing site and we couldn't find notes of where the photo came from).

A. Hi Paul.
adv.
One vendor who I believe licenses this process is Russamer Lab [a finishing.com supporting advertiser]

Regards,

A. Matt,

You need to:

a) make sure the temperature is low - if many rounds of coloring happen prior to gold coloring, your tank may be warmed up.
b) make sure that there is mechanical swinging of holders or some electrolyte circulation - power of 60V locally heats up electrolyte, and some areas can be warmer than others.
c) better to slowly raise voltage - 30 seconds duration to reach 60V. This way you do not overheat parts locally. Most rectifiers have this option of slow voltage raise.
d) if racks surface submerged into electrolyte is significant, it is better to mask racks, so they do not attract much of the power.

Thank You Anna, for the good info.

We have slowed the ramp rate, as you indicated, and have some improvement. We'll be trying the other items you listed in the near future.

Thanks again,
Matt

A. According to Oppi Untrachts book Jewelry Concepts and Technology 5 -10 volts must be ok. Any electrolyte must work ... Hope it helps and Good Luck!

A. All alkaline formed titanium anodizing must be blasted to remove the common white powdery deposit.

A. Robert,

Not all titanium type II anodizing processes create white powdery deposits.
adv: Our proprietary anodizing creates a smooth surface of black (if grade 5) or gray (grade 1-4) surface that does not require blasting.

A. Hi Alex,

I suspect the solution is overheated.

A. The possible ways:
1. cooling down the solution;
2. Masking holders as much as possible, so they do not participate in the process;
3. move electrolyte by swinging holders or liquid; use larger tank.

Make sure you raise voltage very-very slow - up to 30 seconds until it reaches 60V.