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topic 224

Inorganic gold dyes for anodized aluminum (ferric ammonium oxalate)


(1996)

Q. I have a problem with which I suspect you may be able to help me. Some ten to twelve years ago, I had a customer who required a light-fast gold anodize on some extruded sections. We supplied him with samples dyed in a hot ferrous ammonium oxalate solution, and he was quite happy. We got the job, but it only ran for a few months, and since we had no other call for it, we dismantled the bath in favor of our regular Sandoz gold.

Now I have occasion to use the bath again and I can't remember the make-up. I VAGUELY recall that we adjusted the pH to between 5-6, but I'm not really certain about this. I've looked through all of my notes and my references, and I can't find the formulation. Would sure appreciate your help on this.

Regards

Gene Dodge


A. Hello, Gene. Fred Pearlstein, writing in Plating & Surface finishing 2/79, tells us "the most commonly used inorganic pigment is produced by immersing the freshly anodized part in a 20 g/L ferric ammonium oxalate solution at pH 5.0 and 50 °C; this provides an attractive, metallic gold appearance..."

It is often called FAO Gold dye. Perhaps AESF (www.nasf.org) can provide a reprint of the article.

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



May 13, 2015-- apologies, finishing.com misfiled this submittal, and didn't post it until May 28

Q. Hi Ted,

I've visited this site a few times now in order to help me get started with my own anodizing set up. I'm trying to explore gold anodizing and saw your post. I'm wondering how you adjust the pH of a dye solution? Do you just use some common acids/bases to lower/raise the pH of your dye solution?

Thanks very much for your help!

Best,

Raj

Raj Selagamsetty
Boston University - Boston, Massachusetts, USA


Surface Treatment & Finishing of Aluminium and Its Alloys
Wernick, Pinner & Sheasby

May 2015

A. Hi Raj. Since Hurricane Sandy, some of my older trade journals like the referenced issue are in the basement of my son's house and not readily available; so I can't refer to that Pearlstein article for you. You reputedly can get access to it with a subscription to nmfrc.org.

But to answer your specific question, according to Wernick, Pinner & Sheasby: "additions of oxalic acid or ammonia as required" =>

Good luck.

Regards,

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


May 28, 2015

Good day Raj.

I would contact your dye supplier.
I have a black dye and a nickel acetate cold seal, and use dilute NaOH and acetic for pH control.
DYING to try it?

Regards,

Eric Bogner
Lab Tech. - Whitby, On., Canada


May 2015

thumbs up signHi Eric. I assumed that Raj was talking about inorganic FAO dye because of the thread to which he attached his inquiry. But he didn't actually say that, and you might be right that he just wants gold color the easiest way.

Regards,

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


May 30, 2015

A. Hi

Use Oxalic acid and Ammonia to adjust pH.

Good luck
S. Basu

Srimay Basu
Emirates Global Aluminium, U.A.E. - Asansol, West Bengal, India


June 1, 2015

thumbs up signHi,

Thanks very much for your feedback. I was indeed referring specifically to inorganic FAO dye since that is what I'm using to get a gold anodize.

I will attempt to use ammonia/oxalic acid for pH control and see what the results are.

Thanks again for your help with this! Very much appreciated!

Best,

Raj

Raj Selagamsetty
Boston University - Boston, Massachusetts, USA



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