Anodizing Titanium Alloys in Gold and Other Colors

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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

Tom Pullizzi Falls Township, Pennsylvania

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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.

James Watts
- Navarre, Florida

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A. 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 Watts, by the voltage. The voltage is critical.

Good luck.

J.H. Pennings
TNO INSTITUTE OF INDUSTRIAL TECHNOLOGY - Netherlands

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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.

Dave Brackenridge
aerospace plating - Germiston, South Africa

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A. Oxalic Acid, Phosphoric Acid (Coke Cola) Sulfate of Ammonium (Fertilizer), TSP (trisodium phosphate [linked by editor to product info at Amazon])

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

Bernie Wire
wire works

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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.

Kent Backus Fort Worth, Texas, USA

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A. Robert,

I use a trisodium phosphate [linked by editor to product info at Amazon] 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 Fahrenheit. 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.

Howard Bailey