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topic 9084

Discolouration of red and orange coloured anodising layer


Q. We have some anodised Aluminum parts that's dyed in orange and red. After exposure to sunlight (a few days), we've found the colours had gone lighter. I understand some organic dyes are not UV resistant, but can it be improved? And is there any type of dye we can use? Which kinds of colours are not recommended for UV exposure?

WY Wong
- HK


A. If the dyes are not UV resistant, you can not do much about it. However, you can try the following methods to improve your situation:

- Increase the depth of the shade can increase the lightfastness.

- Increase the thickness of anodic coating and/or lower dye concentration and dye at 60 °C (you may need to increase the dye time).

- Increase seal time and seal at boil.

Good Luck.

S. Y. Yuen
- Hong Kong, China


A. Most dyes that all the major makers of dyes make are not to be used for outside exposure. They are recommended only for internal. Clariant has a section of dyes that go by the title of Sandalor (when they were Sandoz chemical) and then the subsequent color they attach to it, for example Sandalor Red, etc etc. These are the only suitable dyes for exterior use and even still their abilities to withstand light are unknown in terms of long term exposure. If anyone has information on test done to confirm lifespan on dyes I'd love to see it myself.

Matthew Stiltner
- Toledo, Ohio

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