Summary for mil-a-8625 color consistency Discussion
Mil-A-8625 color consistency is the key issue here: the poster asks whether the spec gives acceptable/rejectable criteria for uneven anodize color, with areas trending blue and others charcoal or dull. James Watts says the part may be a thin Type II dyed anodize and suggests checking dye color fastness, dye-tank concentration, pH, temperature, and racking; if those are in control, he says the problem likely lies with the anodize process itself. Jeff points to section 3.6 of the specification for guidance, while Robert H. Probert asks for more information about the alloy and process. The thread ends with a note that Willie Alexander was the only one who directly addressed the original question, implying the spec guidance is the main place to look rather than a simple universal color-appearance limit.
Q. Within the spec, is there acceptable / rejectable criteria based on the appearance of the color uniformity? I have seen discoloration trending toward blue, and other areas that look as if it is a charcoal / dark, dull finish.
Jeff Amdahl
Aerospace manufacturing Q.A. – Lakeville, Minnesota, USA
April 21, 2009
 | April 23, 2009 Is this type 2 or type 3 ? I think that this is a type 2 dyed, and the dye is already fading. Check to see what color fastness is for the dye that they are using. Also ask them what test are they using for the amount of dyestuff in there dye tank. Also pH and Temp. If this is all OK, then it virtually has to be an anodize problem. I would be interested to see their racking for the black in some recessed areas and faint violet in others. James Watts Jeff See section 3.6 of the specification for guidance. Willie Alexander Hi Please give a little more information about the alloy and process. Sunny regards
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The color consistency consists two aspects:
1. Within the same part, the color difference is limited;
2. Different production lots from the same anodizer and or from different anodizing supplier produce parts with color difference (of course for the same spec.) is limited.
In your case, the shades at different location of the same part varied so much which I do not think is normal.
John Hu
– Singapore
I see (1) low thickness and (2) work hardening in some areas.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
April 28, 2009
Congratulations, Willie – you’re the only one who addressed the original poster’s question
Bill Reynolds [deceased]
consultant metallurgist – Ballarat, Victoria, Australia
We sadly relate the news that Bill passed away on Jan. 29, 2010.
April 28, 2009
Willie did answer the question directly and correctly, but just in case the original poster (or any future readers) don’t have MIL-A-8625 handy, here is the actual wording:
“3.6 Class 2. When class 2 is specified in the contract or purchase order (see 6.2), the anodic coating shall be uniformly dyed or pigmented by exposure to a solution of a suitable type dye or stain. The color on wrought alloys shall be uniform. Cast alloys may exhibit dye bleed-out or lack of color (or color uniformity) associated with the inherent porosity of the casting. The dyes and pigments used shall not be damaging to the anodic coatings.”
So, the original poster is certainly correct in telling their anodizer that the parts are not according to spec – regardless of cause.
Jim Gorsich
Compton, California, USA
May 26, 2009