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Brown Stains on plated zinc diecastings

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My nature of work is Vendor In-Coming Technician. Why does zinc die casting surface having brown stains after Copper - Electroless Nickel or copper - Brass plating.

Thank you.

Mustafa Taib
- Singapore

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Sounds like cyanide bleedout to me, in which case you would need excellent rinsing, preferably alternating hot and cold several times.

Ted Mooney, P.E.
finishing.com
Brick, New Jersey

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