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Black spots in cyanide copper plating

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Q. On a copper-plated MS Screw, I am facing black marks. To ensure a lengthy shelf life, we need a suitable remedy for the black stains.

Amit Kadam
employee - Pune, India
May 15, 2023

"Electroplating and Electroless Plating of Copper and Its Alloys"
by N. Kanani
from Abe Books
or Amazon
(affil links)

A. Hi Amit. Copper is not a tarnish-resistant surface. You can try a dip in a proprietary benzotriazole copper preservative if you feel the problem is simply the insufficient shelf life of the copper.

But sulfur [affil link] in the environment will cause blackening of copper. And as mentioned on this page already, cyanide copper will often get blackish bleed-out stains.

Please send pics to for posting here, and give us at least your general treatment cycle. Thanks. Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

⇩ Closely related postings, oldest first ⇩

Q. We're into cyanide copper plating, we are facing a problem as mentioned below:-
After plating MS screws in cyanide copper plating by barrel method, after some time on the threaded portion we are finding some black dots on the plated surface. what could be the reason

warm regards,

V Thyagaraj V Thyagaraj
plating shop employee - Bangalore, Karnataka, INDIA
July 1, 2010

A. Hi, V. When cyanide-based plating exhibits dark spots or dark areas after some time, it is usually "cyanide bleedout". The way to solve it is better rinsing: possibly alternating hold and cold rinses, or an ultrasonic generator in a rinse tank, or a neutralizing agent like sodium metabisulfite or at least sodium bicarbonate, possibly a final D.I. rinse. Good luck.


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

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