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Is Blue Alodine Bad?

An ongoing discussion beginning back in ...

TUTORIAL:
(to provide context, hopefully helping readers more quickly understand the Q&A's)

"Alodine" is a Henkel trade name for their chromate conversion coatings for aluminum.
"Iridite" is Macdermid's trade name for theirs.
The slang "chem-film" is often used in the USA.

MIL-DTL-5541 [affil link or DLA] is the most common specification for the process.

Aluminum How-To
"Chromating - Anodizing - Hardcoating"
by Robert Probert

finishing.com has sold 800+ copies without a single return request :-)

2002

I have been acid etching and treating Stearman Biplane parts with Alodine 1201 [linked by editor to info/product on Amazon] . Castings and panels have been coming out of the solution a bright to dark blue color. Is the solution bad or is the color due to copper content of the aluminum? (which is world war II vintage and unknown.) Is a blue conversion coating safe to prime?

Luis F. Villar MD
- Stuart, Florida

November 17, 2021

A. Taken fron Henkel Bulletin ...

"Variations in color result from different alloys, metal hardness,
metal age, method of cleaning, etc."

Alexander Saborio
Painter - San Jose Costa Rica

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