Metal finishing Q&As since 1989

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Appearance of the clear tri-valent chromate over zinc per ASTM B633

December 3, 2009

Hello I have a question regarding the appearance of the clear tri-valent chromate over zinc per ASTM B633, this is because we have 2 different supplier (platers) one for the front and one for the back part, so the supplier # 1 provide a shiny clear color with little of blue color you can see this with naked eyes, and the supplier # 2 provide the parts with a shiny clear color with a little of yellow and light brown, my questions are why those color cannot be the same, and if this is a normal on this type of plating.

Thanks a lot for reading my question

Alex Gavino
SQE - Nogales, Sonora, Mexico

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Hi, Alex. All trivalent chromate conversion coatings are proprietary and supplied by different suppliers, and based on different technologies. Your two plating shop are probably using chromates from two different suppliers and the technology may be different. If you need a color match you are going to have to ask one of the plating shops to change suppliers -- and even then, that is no guarantee of a color match as they may be using different zinc plating baths as well.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
December 4, 2009