Anodizing titanium to green color -- Q&A's

A. It takes very nearly 200 volts to get green. This is serious voltage. Make sure that you have an isolation transformer in the circuit and you have quick blow fuses of the appropriate amperage on the output side. A volt or two will make a fairly significant difference in the color for whatever solution that you use, so experiment.

A. My experience with Titanium anodizing showed that you get different colours with the same voltage, on different titanium alloys. Therefore one cannot exactly say at what voltage you'll get what colour unless he has experience with the same alloy. Also, different colours will be obtained depending on what has been done to your part -- e.g., embossing will badly affect the colour which you'll get.

A. Color anodize on titanium is fairly straight forward. What is not is obtaining a coating that is biocompatible. Contrary to popular belief the solution and cell play a role. I for one am fearful that shops jumping into the market will kill it by offering any finish produced as implantable. This is not a paperclip or nut and bolt market.

(harrumph)
Parts is parts.

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

A. In USA you can buy small quantities of titanium from Reactive metals studio. They sell anodizing equipment and booklet too. Good luck!

A. To get a green colour on titanium is hard - it is the last colour you get with anodising as you raise the voltage before the oxide layer goes grey, and with some alloys you don't get a green at all. It usually takes about 70-90 volts DC, which can give you a nasty shock, so wear rubber rubber gloves ⇦ this on eBay or Amazon [affil links] and avoid anything that could cause a short circuit. However, if you are fully aware of the safety precautions, then try it, with adult help. You need to make the titanium the anode and use a piece of stainless steel as the cathode. For the electrolyte I use dilute sodium or ammonium sulphate ⇦ this on eBay or Amazon [affil links] or phosphate solution. I estimate that a strength of about 1 gram per 100 ml would be enough. If it is too concentrated, a large current will flow and you can get sparking as you lower the sword into the electrolyte - quite dramatic, but not good for the oxide colours! The best way to get the colour you want is to gradually increase the voltage while taking the metal out to check it. Sometimes each colour takes a couple of minutes to develop. The sequence of colours from 5 volts up is brown, purple, dark blue (20 V), light blue, yellow (40 V), gold, pink (50 V), magenta (pinky purple), emerald green (70 V), apple green, grey. Good luck !

A. Hi Jeff. I don't believe that the problem stems from the shape. Perhaps the tooling that does the flaring involves heat or oils that are spoiling the effort. I would scrub the flared area with powdered pumice and detergent and see if it makes a difference. Maybe see if it's possible to bend that tube by hand, and if the stretching alone has caused some metallurgical dislocation that causes blackening at the bend. Good luck.

Regards,

A. Hi, cousin Arivazhagan.
Jeremy has told us earlier on what voltage to apply, and that he uses dilute sodium or ammonium sulphate or phosphate solution as the electrolyte. I think the answer to your question then is to use dilute sodium or ammonium sulphate or phosphate solution at the voltage he suggests, rather than to ask what voltage and what ratio to use for sulfuric acid :-)

Good luck!

? Hi cousin Prashant. Please try your best to frame your question in terms of the answers already offered on this page preceding your question. For example, are you using the alloys and the processing solutions previously described? Thanks!

Regards,

A. Hi Rahul. As you see, we appended your inquiry to a thread on the subject, which should offer some helpful info. Thread 1265 also addresses this -- see the postings on that thread from Jon Quirt and Anna Berkovich. Good luck!

Regards,

A. Green is very difficult to obtain. I start by buffing the material to a very shiny state, then removing all buffing compound with acetone ⇦ this on eBay or Amazon [affil links] Warning! highly Flammable! , alcohol and ammonia.

When it is very very shiny and surgically clean, I suspend in distilled water. I do not touch with hands anymore -- use medical disposable gloves from thereon.

You'll need to etch it next. I use Multietch at about 150 °F with a fish tank air bubbler for agitation. I then etch in this solution (make sure it's fresh, can't reuse it more than once or twice). I let it etch for about 7 seconds, then quickly remove and immerse in distilled water, then wipe it down with a lint free cloth (etching too long removes the finish).

After it's clean again (remember, no touching) -- I reuse the ammonia; here it goes back in distilled water.

To get green I find I need somewhere between 95 and 120 volts DC depending on alloy and other factors (such as preparation). I use 7% phosphoric acid in distilled water. I refrigerate this and even place acid bath in a container of ice so it stays cold.

Put in the piece, use voltage like I said, don't let any part of the electric lead get wet (this can be tricky and require creation of creative fixtures.)

Remove it, it should be green. Start with low end of voltage range and increase until you get the green you want. If you prepare the items for this process methodically, same way every time, you should be able to achieve similar results on similar alloys.

A. Wow! That was a detailed description, Christopher, thanks!

Luck & Regards,

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

A. Problem of achieving green colour is in the solution. At higher voltage you must keep high diffusion. I recommend solution of 0.1 H3PO4 or any NaH2PO4, Na2HPO4 works best, and easily achieves green at about 120 V. By addition of Fluoride salts you may drop down voltage into 90 V. But remember to keep the low amount of acid around 0.1-0.2M.

Hi Marcin. Thanks for the great specifics!

Regards,

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

A. We do 2-tone (blue/grey) anodize on Titanium as a proprietary special process, and the biggest advice I have is to really think through your masking- engineer it well, and don't skimp on the construction. In our case, this meant machining clamp-on masking fixtures with Viton o-rings that then compress tightly against the part and don't allow leakage. Each part has to be literally BOLTED into the masking fixture, and then the whole thing gets tossed in the tank.The high pressure exerted by the fixture on the sealing surface is critical to get a nice clean line between the two different colored regions.