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topic 0741

"Opalizing" of Aluminum


I'm looking after the meaning of "opalescence" or "opalizing" of Aluminum. I think it is a kind of "hard anodizing" of Aluminum, but I'm not sure.

Can somebody help me find more information about this way of anodizing?

Hans Hendriks
- The Netherlands


I did some anodizing of 3003 aluminum in 15% oxalic acid with a 3003 aluminum cathode. The results were very interesting. When the sample was rotated by about 45 degrees, in one angle it showed green, in the other angle it showed a reddish color. Many of my anodizing samples look opalescent.

Dave Fairbourn
- Sandy, Utah


Opalizing is a process invented by Philips in the early sixties. It is a kind of a hard anodizing process with a very specific color.

The color is caused by the combination of the material composition and the composition of the anodizing bath.

The main constituent of the anodizing bath is oxalic acid but there are some other elements involved as well.

The process is called "opalising" because the coating is not transparent (looks like enamel).

A similar process is a German process called Ematal.

Gijs Gerlagh
Philips galvanotechniek - Eindhoven, Netherlands


To: Gijs Gerlagh

Would you be kind enough to give us more information regarding the Philips and Ematal process?

Much thanks

Fred Yeung
- Hong Kong

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