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Ted Mooney, P.E. RET
Pine Beach, NJ
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for Metal Finishing since 1989
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Gold Color Finish for Hard Anodize
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Q. We are facing some similar color issues after hard anodizing II.
Our customer needs dark golden colour after hard anodizing process and we are now getting grey colour after hard anodizing.
Can you please advise me how to fix this types of issue.
Many thanks in advance.
Employee - Rajkot -India
November 22, 2021
A. Hi Sandeep.
Was that a typo in "hard anodizing II"? Not sure if you're doing type II or type III.
1. You could try type 2-1/2 anodizing or oxalic acid chemistry if it doesn't violate your specs.
2. Although hard anodize isn't usually sealed, you could try a chromic acid seal.
3. Although hard anodize isn't usually dyed, you could use a dye of the color you want.
Please return the favor by keeping us appraised of of your progress or lack of progress. Many thanks in advance.
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
November 2021
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A. Hi Sandeep. supervisor - Cicero, Illinois Saporito Finishing Co.   November 24, 2021 November 24, 2021
Q. Can you also advise me how to control aluminium sulphate in anodizing bath? Is aluminium sulphate the cause for burning issues or color variations? Engineer - Rajkot -India |
Dear Mooney sir ,A. Hi Sandeep. Philip's reply crossed in the mail with your posting. It has good ideas including dyeing. 25 microns (0.001") is fairly thin for type III hardcoat but very thick for type II. Even architectural and black anodizing is rarely over 0.0007". Also, 4 °C (40 °F) is neither conventional type II nor type III temperature.
It sounds to me like your customer is looking for and has become familiar with type 2-1/2 anodizing. Usually this will require a proprietary additive or additions of glycolic acid and glycerine rather than just sulfuric acid. Do a search for "MAE anodizing process". But read the rest of this thread first and there is interesting info about doping the aluminum before anodizing.
We want to help you out with all of your problems and not hassle you, but this site has hundreds of readers for every poster, and it's a disservice to the readers if the threads all wander to such a wide extent that it loses most of its usefulness as a research site. So please search the site for the issues that you mentioned that are not related to getting a gold coloration, like "controlling aluminum sulphate in anodizing", "burning in hardcoat anodizing", "estimating anodizing time vs. thickness" (search for "the 720 rule"), and post your continuing questions on relevant threads. Thanks!
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
November 2021
A. Hi Sandeep,
If you start with type III traditional hard anodize, your substrate is going to be some sort of grey or bronze, depending on alloy. So you need to talk to your customer about the limitations of the process, and how important added abrasion resistance vs. color is to them, and work to find a process that works, or if they are stubborn... return a no-quote. In my experience, true sulfuric hardcoat and any pale color are incompatible. And depending on the alloy, sometimes even the promised color of the dye will be nowhere near what you expect.
Best of luck.
Rachel Mackintosh
lab rat - Greenfield, Vermont
December 24, 2021
⇩ Related postings, oldest first ⇩
Q. We are an engineering company manufacturing factory automation part, and we have a customer's requirement that needs hard anodize parts with a gold finish. We've sent parts for anodizing to our suppliers and they usually come back with a dark finish. How can I get the gold finish?
Edward Layengineering - Kuala Lumpur, Malaysia
2004
A. What is your means of gold color, is it gold plating on the aluminum parts? Do you know different grade of aluminum will come out the different color after you do the anodizing?
Goh Boon Han- Muar, Johor, Malaysia
2004
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Aluminum How-To"Chromating - Anodizing - Hardcoating" by Robert Probert Also available in Spanish You'll love this book. Finishing.com has sold almost a thousand copies without a single return request :-) A. "Hard Anodizing" means different things to different people. To the Military Specification writers it merely means a heavier thickness, usually about 0.002 inches thick, and hardness it not addressed. To me it means a small pore which which is created by a cold temperature and high current density. So far your gold color is dark because the pore is very small and that tells me that you are getting one kind of "hard coat". By anodizing at a higher temperature with a glycolic/glycerin type additive you can get thickness (so called "hard coat") and a larger enough pore to get bright gold dye adsorption. Another way is to use what some call "Architectural Hard Coat" which takes place in an electrolyte that contains sulfatholic acid and derives it's gold color from the oxide formed from manganese that is alloyed (or mixed) into the metal. Here you buy a special metal from the aluminum supplier that is "doped" with an impurity (usually manganese) that comes out bright gold color when anodized in sulfuric with sulfatholic acid. Any of the four big aluminum suppliers can furnish the details.  Robert H Probert Robert H Probert Technical Services Garner, North Carolina  2004 A. Mr Goh It is not gold plating on the aluminum, rather gold color. the aluminum grade is 6061. I know different grades will affect the color. I've run test for black anodizing before. Even the country of origin affects the color. What I require is for a hard anodize treatment that will also yield a gold color finish. Edward Lay [returning]engineering - Kuala Lumpur, Malaysia 2004 |
A. Try having the parts hard anodized at lower current density (18 ASF) and only anodize .0005-.0008" thickness. A 5% nitric acid dip before dying might help also.
Good luck,
Bill GraysonMetal Finishing - San Jose, California
2004
A. The color of Hard coat is a factor of what alloy, that is being hard coated. A Gold color after hard coating means the alloy is a 7000 series, like 7075, A dark gray hard coat is 6000 series like 6061-T6, different heat treats different machining temps can cause different shades of color.
Chris Snyderplater - Charlotte, North Carolina
2004
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