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Want easy way to tell if a clear anodized part is properly sealed

I have a label on an anodized part that once removed is leaving a mark that cannot be cleaned off. We have attempted several cleaners but none have made a difference. I think that this part may not have been properly sealed and the adhesive from the label is etching the coating. I would like to know of an easy way to tell if a clear anodized part is properly sealed.

Scott Huffman
Synetics Solutions Inc - Portland, Oregon, USA
2005

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First of two simultaneous responses --

ASTM B136 is a seal integrity test that will quickly show if an anodized surface is sealed. Easier yet is coffee or any other staining media - if it is adsorbed by the anodize, if isn't sealed! Usually an unsealed anodize feels sticky to touch.

A good seal is the difference between a good anodizer and a "pore" anodizer!

Milt Stevenson, Jr.
Syracuse, New York
2005

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Second of two simultaneous responses --

Splash on some dye and rinse off, if the dye color stays, it ain't sealed. Many job shop anodizers do not take the trouble to properly control their seal tanks, The seal is a very dilute solution therefore it is very very susceptible to slight drag-in of impurities (tap water calcium and chlorides) which prevent the aluminum oxide from becoming fully hydrated. Have your anodizer make-up a new seal in a 4 liter beaker in the lab with distilled water and whatever sealing compound he uses. Run parts in the tank and the beaker and evaluate. If he will not do this, find another anodizer.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2005