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Light Fastness of Anodised Panel

Q. I work in the aluminium industry in Australia and would like to find out more regarding various marks and imperfections on anodised aluminium.

Can you recommend a technical journal or book that I could buy that would cover this?

I'm thinking of problems such as pitting, fishtails and white marks that we experience from time to time. Also is there anything on the net you're aware of ?

Kind Regards

Stephen Charlton
- Melbourne Australia

A. Arthur Brace (UK) wrote a book about "Surface Defects". This was information and pictures originally gathered by Alcan Aluminum. It is a good reference book and can be obtained from either AESF or Metal Finishing Magazine (both US).

Charlie Grubbs
- Alpharetta, Georgia

A. You may want to take a look at the revision of an old book: Aluminum: Technology, Applications, and Environment; ISBN number:0-87339-406-2. Published by The Aluminum Association and the Metals, Minerals and Materials Society.

Lee Branch
Richmond, Virginia


Q. Dear Reader,

Q. Well, I don't know exactly where to begin but just to assume that you are familiar with this process. This is about sealing process in the anodising(the last process in the anodising).

We have a product using clear anodise panel and the problem is,it get easily turn the surface from clear into yellowish or light fastness is poor.

We are looking at increasing sealing temperature to the normal temp, which is 96C to boiling but after light fastness test, the panel change color after 20 hours (Using Suntest apparatus from Heraus).

What do you think we should do to solve this yellowing panel.

Is it to do with the additives use in the sealing bath. Please let us know if you know what additive best for sealing bath.

On the other hand, are we really on the right track solving yellowing problem in the sealing bath? Maybe it has to do as well in the anodising bath?

By the way, we are not anodising company and just doing this research to help our vendor to cure the problem.

Is there a book you can recommend about anodising?

Cheers and best regards,


Butch Arcenal
audio electronics- Hong Kong

A. It appears that the normal vendor/customer relationship has been violated in this case. Your product should pass 30 hours lightfastness using the Suntest apparatus from Heraus, and the vendor should agree to supply this as a lot acceptance criteria under some sampling plan.

The lot size should not be larger than the amount of panels processed in any one eight hour shift.

If your vendor tells you that they can't supply it, look for another vendor. If your vendor accepts the condition, and the panels fail, then you have to go back to the vendor to find out what happened.

This falls under corrective action in ISO9000 because the panels fail the acceptance criteria. What explanation does your vendor give for the failure? -tom

tom pullizzi monitor   tom pullizi signature
Tom Pullizzi
Falls Township, Pennsylvania

A. I'm not familiar with the testing apparatus you're using, but I would guess that there is some residual contaminants in the anodic coating that is oxidizing upon exposure to UV light. I would look at your vendor's rinse stations first, before looking at the seal tank.

Gerald Janssen
- Chicago, Illinois

A. Regarding the problem of yellowing of the anodic film following sealing and UV testing. I suspect that the cause is related to impurities in the anodic film. I suggest investigating the iron concentration in the sulphuric acid in the anodising tank. Oxidation of small quantities of iron can give rise to a yellow appearance. I do not believe that the problem is a function of the seal temperature or contamination of the seal solution.

Brian Peter Anderson
surface treatment - England

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