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topic 28863

Problems in cyanide copper plating

A discussion started in 2004 & continuing through 2017 . . .


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
Popat Patel
    Howard Finishing
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
Galva, Illinois

November 24, 2011

Q. We run a cyanide copper flash process and are getting a blackish deposit which seems thinner than usual at the high current density on parts and test panels. The copper content is mid range at 49 g/l and the cyanide level is just above mid range at 32 g/l. We have changed all the anode bags and peroxide treated potential iron contamination.

I'm running out of ideas fast and would appreciate any thoughts on this!!


Emily Gardiner
- Poole, Dorset

November 25, 2011

A. Hi Emily,

Problem could due to too high carbonate content (> 120 g/l) which reduce cathode efficiency, or organic/sulfur contamination. Perform carbon treatment or bath dilution may help.


David Shiu
David Shiu
- Singapore

November 29, 2011

thumbs up signThanks,

We have been filtering through a carbon filter for 4 days. There is a marked improvement. I will also test the carbonate level to make sure this is not an issue.

Emily Gardiner [returning]
- Poole, Dorset, UK

November 29, 2011

thumbs up signThe problem has been solved on Brass components with carbon filtration but not on Steel. I have since tested the carbonate level and found it to be 102 g/l. So in the lab have performed a half dilution and a hull cell. It looks much better on both materials.

Emily Gardiner [returning]
- Poole, Dorset, UK

January 8, 2013

Q. We use Copper cyanide bath for copper flashing on steel parts. Recently, in my absence from plant we are experiencing a problem. What used to take 2 minutes now takes 10 minutes to plate. Concentration of free cyanide is 2.4 oz/g, pH is about 12 and carbonate 36 g/l. Please help me resolve this problem.

Veena Mandlay
- Carpinteria, California, USA

January 11, 2013

A. Hi Veena.
The free cyanide/pH/carbonate contents sounds about right. Two questions come to mind.
1. What is your copper cyanide content?
2. Is this a 'sodium' or 'potassium' base cyanide copper bath?

SK Cheah
- Penang, Malaysia

January 18, 2013

Q. Mr. Cheah,
I have the same doubts you have about Copper Cyanide content but I don't know how to determine that. I was thinking of adding a little portion of Copper Cyanide in the bath to see if there is any improvement. I have carbon filter in the bath which is helping little bit. Also my bath is Sodium Cyanide base. I appreciate your help.

Veena Mandlay [returning]
- Carpinteria, California, USA

January 23, 2013

A. Hi Veena.
1.Copper Cyanide content can be determined by titration.
Take 2 ml of sample solution. Add 15 ml of conc. Nitric Acid. Heat to blue color (this to be done in an exhaust hood). Add 100 ml of DI water. Add conc. ammonia to blue color. Heat to 140 °F. Add PAN indicator. Titrate against 0.1M EDTA. Color change from purple to green.

CuCn ( oz/gal ) = ml x 5.971 x M

2.Take care when adding Copper Cyanide . An addition of 1 kg CuCN needs an addition of 1.1 kg Sodium Cyanide with no increase in free cyanide.
Good Luck.

SK Cheah
- Penang, Malaysia

February 1, 2013

thumbs up signThank you Mr.Cheah. My tank is getting better.

I have another problem in my Nickel Sulfamate tank. I'm getting some black/burned spots after electrolytic plating. And specially where the parts get in contact were current is passing. Most component in my tanks are at an optimum level except Nickel which is between 11.5-12.5 oz/gal. I performed carbon treatment, added stress reducer and plated dummies before plating good parts. My plating is on 1030 steel and I copper flash before nickel plate. Please advise. Your answers are always so useful.

Veena Mandlay [returning]
- Carpinteria, California, USA

March 3, 2013

Q. I have a related Question I wish you can help me, I made a small in my lab as a test I wanted to simulate the plating unit in my factory the bath consisting of cyanide copper bath, a flash one of (120 g/L CuCN) and (138 g/L NaCN) and it went very well, but when I add 40 g/L NaOH to simulate the thick deposit bath the anode became black and passive ! it only works fine if I lowered the current but if I did the deposited layer become similar to flash bath so what is the advantage ! is there something missing !? it just work properly in the factory plating unit so I hope you tell my what have I done wrong

Ahmed Samir
- Cairo, Egypt

March 7, 2013

A. Good day Ahmed.
I think that you have a formulation problem.You might want to look at these formulations as a guide.

General Purpose strike:
CuCN - 30 g/l
NaCN - 48 g/l (Total Cyanide)
FNaCN - 11.25-15 g/l(Free Cyanide)
NaOH - 3.75-7.5 g/l
Na2CO3 - 15 g/l
Rochelle - 30 g/l (Tartaric Acid-Aids in anode corrosion and adjusts Cu Metal Conc. and acts as a grain refiner)
Ph - 12.5-13.5 Use Dilute Acetic/NaOH to Adjust

Strike-Plate Bath:
CuCN - 42 g/l
NaCN - 52 g/l
FNaCN - 5.7 g/l
Na2CO3 - 30 g/l
Rochelle - 60 g/l
Ph - 10.2-10.5

Hope this helps.

Eric Bogner
- Toronto, Ontario, Canada

October 10, 2013

Q. To Experts,

I have problem in my Cyanide copper plating baths. The problem is red spot and red patches. How to solve this issue? Kindly give me suggestion to solve. Copper metal is 50 g/l, free potassium cyanide 25 g/l in the plating solution.

Thank you

- Singapore

February 25, 2015

Q. Hello, we are having trouble with the free cyanide concentration in our copper cyanide electroplating procedure.

We have 10 baths 1 m3 each, with about 9,5 g/l free CN, 61 g/l Cu and 130 g/l CO3. We have titanium baskets with solid Cu as anode.

Each day we add almost 1m3 H2O from the first rinse, we add almost 350 kg Cu in the baskets and almost 30 kg NaCN. We make chemical analysis of the bath every day. Lately we have black spots after the polishing and we can't bring the appropriate balance to the bath (concentration of Cu and CN). Any idea how we could increase the concentration of the CN and have the same concentration of the Cu (60 g/l) in the solution? Why do we have so many fluctuations of the Ampere-hours that we need to electroplate the same amount of Cu? (We put in the barrel 100kg and it takes 2500 - 2800 Ah to succeed 25[?]m)
Thank you for your help.
Matina Tsolaki


March 20, 2015

Q. I am a newcomer for cyanide copper plating industry. I am badly in need of having standards for following. Please help me sir.

1) CN concentration in bath
2) Cu Concentration in bath
3) pH value
4) Desired density in plating bath.

5) What are details (bath status) can be taken about plating bath, by looking at density value?

6)What are the details can be taken about plating bath, by looking at pH value?

7)How to measure Anode cathode current density? what are the details can be taken by looking of this value?

8) what is the importance of temperature?

I am looking forward to hear from you at the earliest.

L.K. Wijerathne
- Sri lanka

March 2015

A. Hi L.K.,
Please view the cyanide copper plating section of the digital version of the Metal Finishing Guidebook, which addresses those issues with a nice 4-page introduction, then get back to us with your remaining questions. That on-line book is no longer supported as Elsevier Science has ceased publication of Metal Finishing, so view it while you can :-)
Good luck.


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

July 27, 2015

Hi, Wijerathne
Your cyanide plate bath have anodes polarise problem because of the ph is not right. Once your anodes polarise you lose coverage on parts. Make sure caustic concentration in cyanide bath is right.

popat patel
Popat Patel
    plating shop
Roseville, Michigan

March 30, 2015 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Dear sir
We are having cyanide copper bath which seems to be declining day by day. We are making all our efforts to increase the concentration above 60 gm/Lt but it's not working. After adding lots of chemicals they are getting wasted because the annodes are getting black after two days with applying current 2amp/DM square. So, sir, kindly reply if this problem has some solution.

kirti ranjan patra
- vadodara, gujrat, india

March 30, 2015

A. A possible cause is low free cyanide concentration.

Lyle Kirman
Consultant - Cleveland Ohio USA

Black film on anodes in cyanide copper plating leading to decrease in copper coating

April 7, 2015

Q. Hi everyone,

For about a year now we have been facing major problems with our cyanide copper plating tanks.
We normally do a 15 minute copper plating and then the final finish which might be brass on nickel.
But since a year we have been noticing that after we do a clear powder coat (heated) after a while black patches start showing up on the item. Items are manufactured in Mild Steel Sheet.
Also, The copper anodes get covered in a thick black film very quickly after cleaning.

We have tried the following to improve the condition :
1) Maintaining pH levels at 10.
2)Addition of Acetic Acid.
3)Carbon packing and running of filters.
4)Increasing copper metal through Rochelle copper salt addition.
5)Increasing water cleaning decreasing & polishing processes before copper plating.
6)Diluted sulfuric acid and water cleaning before and after plating.
7)Cleaning of plating tanks thoroughly by taking copper water out.
8)Heavy Sodium Dichromate dip for clear finishes.

But still no result, plating is weak and prone to failure. Plates turn black quickly and Amps stay low. Current being passed has dropped compared to year back.

Please advise.


Bharat Krishna
- Delhi,India

May 1, 2015

A. Please check anode alloy composition. Prior to cyanide copper, cyanide activation is compulsory.


Karthikeyan Ponnusamy
- Bangalore, Karnataka, India

May 2, 2015

A. Good day Bharat.

You have not given information about the concentrations of the copper solution.
I would suspect that at a pH value of 10, it would indicate a very low sodium hydroxide concentration.
Why are you adding acetic acid? I would suggest a pH value of minimum 12.5,giving you approximately 1.25 oz/gal sodium hydroxide.
The acetic will lower the pH, and cause the bath to lose conductivity and retard anode disolution = the anodes will not remain active and can polarize, causing the black film. This will lower the copper concentration, and adding Rochelle salts is only successful for copper increasing IF the anodes can function at a proper pH value.
Concerning the black patches, I would suspect a bleed out situation from the copper solution, or your reference to a heavy dichromate dip.
How heavy is this, and what is your process?
Hope this helps, but more data from you could solve the problem.


Eric Bogner
Lab Tech. - Whitby, On. Canada

May 12, 2015

A. Hi.
For cyanide copper plating,
1. Black anode films indicate low hydroxide and low free cyanide.
2. Black/brownish mark after brass plating indicate cyanide bleed out. After brass plating, a sulfuric acid dip would help.
Good Luck.

SK Cheah
- Penang Malaysia

May 9, 2016

Q. Hello...
Actually I am copper plating zinc based castings.
I am bath fitting manufacturer. I am copper plating faucet heads and, later on, nickel and chrome plating is done.
The problem I am facing is that after plating small dots appear on the surface of castings. These small pores appear like small shining stars.
What I feel is material gets etched. Due to that I am facing this problem. Can someone suggest me how to reduce my precleaning of the buffing compound?. Because more cleaning leads to this problem.
I am rinsing the material with H2SO4 after cleaning process. Are there any mild acids for rinsing?

Also I am facing problem of throwing of copper with deep edges.
How to increase my cyanide copper conductivity.?

Like we use H2SO4 to increase conductivity of copper acid.
Is there any alternate for cyanide copper also?
Does sodium thiosulphate increases its conductivity?

nikhil sharma
- india

May 9, 2016

A. Hello Nikhil, If you are adamant in your belief that the etching / cleaning cycle is the culprit of your problems go to that process and examine the fixtures after etch and pre- clean to see if there are imperfections on the surface. The parts may not be etching completely. As far as the CN Cu bath have the bath analyzed completely for free CN, CN Cu, sodium or potassium hydroxide, and carbonates. If all the chemistry is within spec and you still get poor throwing power in recessed areas you may have to carbon treat the bath. There are alternatives to CN Cu plating, alkaline Cu solutions are commonly used. Contact a reputable supplier of plating solutions, and they can help you.

Mark Baker
Process Engineering - Phoenix, Arizona USA

May 12, 2016

A. I have never been able to "sell" this idea to anyone else, but when I have to plate onto zinc base die cast, I prefer to pure zinc plate first, then go on to the copper-nickel-chrome.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina

Editor's note: Mr. Probert is the author of Aluminum How-To / Aluminio El Como

May 18, 2016

A. More cyanide? That solves most problems with that bath.

dave wichern
Dave Wichern
Consultant - The Bronx, New York

October 29, 2016

Q. Hello... In copper cyanide plating I am facing multiple issues.

At first I was facing issue of low throwing power. At low current density areas I was facing issues of low coverage.
After that I decided to add 1 kg of sodium cyanide to the solution.
After this the issue of covering has been solved. But now the job is having burnt likes patches. I cannot recognize it as burning or something else. But you can say that it is like roughness all over the job.

The tank is of 650 litres.
Should I add copper cyanide to the bath.

I had never made addition of caustic to the solution.
Does caustic helps in increasing throwing power.
Does caustic causes roughness on the job?

What is the main sodium thiosulphate in cyanide bath.
Is there any regular addition required.

Nikhil Sharma [returning]
- jalandhar, punjab, india

December 1, 2016

A. If your free cyanide is OK (1 - 1.5 oz/gal, if memory serves) you might try adding some Rochelle salts (sodium potassium tartrate).

This is not easy to test for; a modest addition (0.5 oz/gal) will not hurt.

dave wichern
Dave Wichern
Consultant - The Bronx, New York

December 6, 2016

A. Good day Sikhil.

From your photo, it is apparent that this bath is an acid copper. The anode bags appear to be blue in colour. If this is true, do not add any more cyanide.
In cyanide copper baths, hydroxide will increase bath conductivity, aide in anode dissolution, causing the metal content to rise. Watch the pH here.
Rochelle salts act as a grain refiner, and also aid in anode dissolution, causing the metal also to rise.
In acid copper baths, the ratio of sulfuric to sulfate is important eg: 1:4 max., as sulfate has a limited solubility. What is the chloride content, and are you within range of the brighteners/carrier concentrations?
Come back with more specific info.


Eric Bogner, Lab. Tech
Aerotek Mfg. Ltd. - Whitby, Ontario, Canada

December 1, 2016

Q. Hi,
I'd like to have more information regarding Mr Robert H Probert's suggestion to use pure zinc to plate on zinc cast alloy's. Is it melting zinc or is it acid zinc?


anders sundman
Anders Sundman
3rd Generation in Plating
Consultant - Arvika, Sweden

December 2016

Hi Anders. I'm sure Robert is speaking of zinc electroplating not hot-dip galvanizing. Electroplating of zinc castings with zinc is also often done before chromate conversion coating instead of trying to directly chromate conversion coat the casting.


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

December 5, 2016

Q. Hi Ted,

Did you know if it in cyanide, acid or alkali zinc they plate zinc castings?


anders sundman
Anders Sundman, 4th Generation Surface Engineering
    Sundman & Nylander AB
Arvika, Sweden

December 2016

A. Hi Anders. Several respondents on letter 16200 recommend alkaline zinc plating of zinc diecastings before chromating. Although I am not personally familiar with Robert's idea of zinc plating zinc die-castings before copper plating, from that it would seem that alkaline zinc would be the best process.


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

Cyanide copper plating pits in low current density areas

December 15, 2016

Q. I have tried carbon treating my cyanide bath. It has helped a bit. But the problem is not solved completely. At low current density areas. There is pitting-like patterns. The problem is coming on flat surfaces at low current density areas.
At high current density areas, there is no pitting.
The pitting looks like small dots all over the surfaces of low current density areas.

I am not using Rochelle salt at all.
My bath is completely based on copper cyanide and sodium cyanide.

There was no such problem in the beginning.

Whenever problem arises I add 5 kgs of copper cyanide and 7.5 kgs of sodium cyanide. It generally resolved my issues in the past.

But now carbon treating and additions of copper cyanide and sodium cyanide is not helping.

While carbon treating I had used 500 grams to 650 litres of solution.
It is adamant to the solution?

I had also tried dummying.

In the dummy also small bubbles like roughness is appearing on low current density areas.
Is this pitting because of impurity or I need to add some copper cyanide and sodium cyanide to the solution?
Please help me out.

Nikhil Sharma [returning]
- jalandhar, punjab, india

March 20, 2017

Q. Hi.

Sorry, I have another request about copper cyanide bath: after plating and hot drying, the workpiece's color converts to orange.
Can you help me about this problem?

Asmaa el-sayed
Chemical Engineer - Alexandria, egypt

April 11, 2017

Q. Hi,
I am Facing problem each time I put sodium cyanide in copper cyanide bath, it converts to brass deposit.
Analysis sodium cyanide 99.9% and there isn't zinc, and if we put sodium in another copper bath it's ok
Can you help me about this problem in the bath and the source of zinc ions?

Asmaa el-sayed
Chemical Engineer - Alexandria, egypt

April 17, 2017

A. Hi Asmaa,

Zinc ions might come from copper anode or other plating accessories like anode basket, heater, circulation pump, etc.


David Shiu
David Shiu
- Singapore

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