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How do you Objectively define Superficial Staining?

From FED-QQN-290 (replaced by AMSQQN290) , 3.4.2: "The nickel plating shall be smooth, fine grained, adherent, uniform in appearance, free from blisters, pits, nodules, excessive edge build-up and other defects." In the same paragraph it turns around and says, "Superficial staining which has been demonstrated as resulting from rinsing, or slight discoloration resulting from baking operations to relive embrittlement, as specified above (see 3.2.11), shall not be cause for rejection."

Similarly,

From ASTM B633, 7.5: "The surface of the electroplated article shall be uniform in appearance... The coating shall not be stained or discolored. However, superficial staining that results from rinsing or slight discoloration resulting from drying or baking operations to relieve hydrogen embrittlement, shall not be cause for rejection."

As a customer who receives a finished part, I am frequently receiving parts with stains/discolorations. How am I to determine what has caused the staining/discoloration? Furthermore, how am I to determine terms such as "slight" and "superficial"? We all know that workmanship is a very subjective thing, but to have competing requirements with no clear delineation defined in the specification is very frustrating, especially when you are not a process expert on finishing. Any thoughts/suggestions on ways to proceed?

Jonathan Severino
Aerospace Supplier - Piscataway, New Jersey
2005

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There is nothing that limits you to exactly QQ-N-290 or ASTM B633 and no more, especially when you speak of aesthetics. You can simply say "plate in accordance with ASTM B633, except that, in addition to and not withstanding any provision in that specification, staining must be held within the boundaries delineated in Appearance Standards Sample Board."

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2005