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"Our copper plating anodes are turning black"

Current question:

September 29, 2021 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. We are using Cyanide Copper strike bath. Bath is continuously heated, circulated, and filtered. Concentrations (especially Carbonates) are tightly monitored.

Anodes are bagged Copper elliptic rods (Oxygen Free Copper).
Few inches above the liquid level anodes rods are bolted to Copper hooks using steel bolts. There is always accumulation of dark black substance/residue at the upper part of the anode bar, in the bolt holes, and around the bolts ==>

There are no signs of black residue under the liquid level. Also, the steel bolts are not damaged (not etched).

Any ideas WHAT is this black substance and WHY it is formed?
(on the photo only remaining residue is shown; majority of it was rinsed away)

Leon Gusak
- Winnipeg, Canada

Closely related Q&A's, oldest first:


Q. I have a problem with copper anodes turning black in the copper plating bath. at 40 amps and higher.

potassium hydroxide
potassium cyanide
free potassium cyanide
copper cyanide
plating on copper and kovar and nickel parts

Thank you,

Randy Aguilera
- California

"Electroplating and Electroless Plating of Copper and Its Alloys"
by N. Kanani
from Abe Books
info on Amazon


A. Randy,

Your cyanide copper bath anodes turning to black, I would like to check potassium hydroxide & potassium cyanide concentration (may be too low). Looks like you loss conductivity in your bath. Check contacts on your anode baskets on copper buss bar (maybe did not make good contact). If you add copper anodes in baskets every week that means you have good contact. Usually if you do not plate it's going to black automatically, and when you start to plate, black layer came out from the anodes.

popat patel
Popatbhai B. Patel
electroplating consultant - Roseville, Michigan

To minimize search efforts and to offer multiple viewpoints, we combined previously separate threads onto this page. Please forgive any resultant repetition, failures of chronological order, or what may look like readers disrespecting previous responses -- those other responses may not have been on the page at the time :-)


Q. In our factory we use the cyanide bright copper electrolyte which is based on potassium cyanide and is used for depositing bright copper layers on zinc die cast,the problem here are:
1- Lower deposition rate in the low current density areas(abdominal cavities)
2- Spotting parts on the surface of the article 3-Dark brown or black color on the anode surface. Please tell me how I can fix these problems.

Ashraf Abbas
chemist - Alex, Montaza, Egypt


A. ASHRAF, you have problem in your copper cyanide bath, low coverage, check the caustic potash concentration in copper cyanide bath looks like it's too low.
Second, spotting problem: check raw material.
Third, black color anodes: 1) you have polarized anodes in your copper cyanide bath, reason for black-- check caustic potash or soda concentration and rochelle salt concentration in copper cyanide bath. If black color anode in beginning to plate is normal only after plate is pink color. After plate still black color anode , I think you have really conductivity problem in your copper cyanide bath.

popat patel
Popatbhai B. Patel
electroplating consultant - Roseville, Michigan



I think you have a different problems in your copper cyanide tank so let us deal with the tank from the beginning

1- first you must check by the chemical analysis of the tank solution the copper content and the free cyanide content . and add the rochelle salt
2- you must check the pH of the solution it must be from 12.2 to 12.8 points (NaOH), maybe with zinc die casting from 9.5 to 11 points
3- you must remove the organic contamination from your tank by active carbon filtration
4- you must check your copper anodes and add if it need
5- you must filtration your tank to remove any colloid matter in your tank
6- you must check the degree of agitation 5- you must remove zinc resulting from die casting by electrolyzing at 2-3 amp/sq ft.

Finally after these points I think the bath will give you abetter quality, thanks.

Aly Gomaa
- Cairo, Egypt


A. Hello,

The previous two gentlemen had very good points. Just for kicks, I would also check your Carbonate concentration. High carbonates with low agitation has caused anode polarization in my facility.

Good Luck

Trent Kaufman
Trent Kaufman
   electroplater - Galva, Illinois

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