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Zinc-Nickel Plating? What are the colors possible?


Q. Presently we are operating a Barrel Zinc plating plant. I would like to know about the Zinc-Nickel plating to enhance the corrosion resistance. My questions are: 1.What is zinc-Nickel plating? 2. What modifications are required to incorporate zinc-Nickel plating? 3. What are the different color finishes possible with zinc-nickel plating? It would be of great help.

v g rajendran
V. G. Rajendran
- Trichy, Tamilnadu, India


A. Hi VG. Zinc-nickel plating is the plating of an alloy of nickel and zinc. One supplier (or more) claims that about 6% nickel is the magic number to get the electrochemical potential where it needs to be for best corrosion resistance.

To my knowledge, zinc-nickel is only available as a proprietary process, so you need to pick a supplier and work with them. But it is available either as an acid or an alkaline process, and you have not said what kind of process you are using for zinc plating so it is hard to generalize on the changes needed to your plating line.

This is a cathodic, protective plating, not a decorative process, so the 'colors' of the conversion coatings are not exactly picked; rather they result from the chromate conversion coating. Some people call the color "purplish" compared to a conventional yellow chromate. But I believe black is also an option, and clear as well. Good luck.

Ted Mooney,
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

Can't get jet black passivation on Zinc-nickel plated parts


Q. My customer spec. is to have jet black passivation, whereas our process that produces brownish tint with black colour after passivation. What is the possible remedy to get jet black colour?

Manager - Chennai, Tamil Nadu, India


A. Does it have to be zinc-nickel plating, Parthasarathy? I think you'll find that reliable blacks are easier to obtain if the plating is zinc-iron because of the iron content. Good luck.

Ted Mooney,
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey


A. Hi!
In your letter there is no clear picture about plating. The substrate should be Zinc (acid) plated, followed by nickel plating. Then the thickness should be more than 20 micron. If the substrate is plated like that you can achieve the desired colour.

- Bangalore, Karnataka, India.


A. Please verify with your chemical supplier; the latest developments in trivalent chromates will help you to achieve with 80 to 90% Jet black finish (acceptable level)

p gurumoorthi
P. Gurumoorthi
    electroplating process chemicals
Chennai, Tamilnadu, India


A. Parthasarathy,
Please give more details about your customer spec. and also full details of what is your plating process. There are lots of developments happening in Zinc plating.
Alkaline cyanide-free Zinc-iron plating, followed by trivalent passivation is the answer. If you come out with more details, you will get good suggestions.
P.S. It is nice to see Gurumoorthi back!

t k mohan
T.K. Mohan
    plating process supplier 
Mumbai, India


A. Dear Mr Parthasarathy,

Try doing an XRF analysis of the Nickel - Zinc percentages on the parts that don't look so good with black. You may find that they have a higher percentage of Nickel in them
and you may have to increase 2-3% of Zinc in the plated alloy to get a pleasing black.

Khozem Vahaanwala
Saify Ind supporting advertiser
Bangalore, Karnataka, India

saify logo

Color Variation on Zinc Nickel Plating


Q. I have a plating supplier that sent me some parts with a good corrosion protection but the parts we have been getting have been gray finished. Now we received a new batch of material "blue" -- the supplier is stating it is a normal process variation and should not affect the functionality of the parts. What do you all think?

Ruben Duran
- Juarez, Mexico


A. Buenas Diaz,

He should let you know what's the difference between the "grey" ones and the "blue" ones.

Saludos cordiales,

Dominik Michalek
- Mexico City, Mexico


A. Ruben Duran

This may be due to latest trivalent chromate over zinc nickel plating available in the market. However normally zinc nickel alloy with trivalent blue produces blue nuances are accepted. This will not alter functional application of zinc nickel plating. We are facing similar problem in India. The coated piece shall exhibit base metal colour (grey) or blue nuance (both are accepted colour).

p gurumoorthi
P. Gurumoorthi
    electroplating process chemicals
Chennai, Tamilnadu, India

March 10, 2012

Q. Facing problem in zinc nickel --

After doing zinc nickel plating the component becomes black after dipping in trivalent passivation.

- Ludhiana, Punjab, India

March 26, 2012

A. Vikram,
Alkaline Zinc-Nickel plating process may be considered as a typical Alkaline zinc plating process with added "impurities" of Nickel in ppms say from 600 ppm to 12-1500 ppm.So you can expect a color change in passivation and it will have a blackish tint but without patches. Also remember there are special chromates for Zinc-Nickel process. Ed Budman rightly said that excess Nickel plays havoc with passivation color. The buyer has also to be educated and shown the color before finalizing the acceptance level of the color. Even the so-called giants in Automobile Industries still go for aesthetics in Trivalent blacks and Zinc Nickel passivation colors. Plating Voltage plays a big role in this system. It is advised to give lesser volts say 3-3.5 to get an even mix of Zinc & Nickel with acceptable percentage. Remember if you increase the voltage you will get a good shining plate color which will not give the property of Zinc- Nickel plating and you will have more Nickel on the HCD (flaking deposit) and less on the LCD.....

t k mohan
T.K. Mohan
    plating process supplier 
Mumbai, India

Nitric acid dip turns the Zinc-Nickel plating black

May 19, 2013

Q. Sir,
I have just started alkaline zinc-nickel plating bath. My problem is Plating gets dull/black in nitric acid.

At present the bath is having 12 gms/lts zinc and 1.8 gms/lts nickel. But I haven't use it for 2-3 months after the bath make up; does it affect the quality?

Tarang Guru
Plating shop - Gujarat, India

June 19, 2013

A. Hello Mr. Tarang,

I hope you solved your problem already, but if you didn't, you should add some (0.5 cc/liter) purifier (your vendor should have alkaline bath purifier for this use) and use the bath for a couple of hours to electrolyse (at low voltage and current, 2-3 Volts) the brighteners and levelers. Then you should run a Hull test and titrations to add sodium hydroxide, zinc and nickel if it needs to...

Just when you have done all of this, start with your production with actual parts. I do not recommend to use left aside baths without electrolysis, because you could get some impurities into the surface of your part. The black spots could be free nickel, so you may need to add some nickel leveler. All this may appear in the Hull test!

Hope this is not too messy and helps you! Regards,

Daniel Montanes
- Cañuelas, Buenos Aires, Argentina

June 22, 2013

Q. Sir,
Thanks. I did the same and already started the plating, but my chemical supplier has suggested to me to avoid nitric dip before passivation. Is it advisable?

Tarang Guru
Plating shop - Gujarat, India

March 19, 2014

Q. 1- What is the best bath composition an operating condition for electroplating of bright Zn-Ni? (for a thesis project)

2- What is the solution for dark appearance of electrodeposited Zn-Ni alloy?

I have some options as below :

mostafa dezfooli
- Iran

Electrodeposition of Alloys
by Abner Brenner

March 2014

A. Hi Mostafa. You haven't told us what you are up to and trying to do, which makes it a bit tricky to reply. As you can probably tell from this and other threads, the usual approach in the Americas, Europe, and India is to buy packaged solutions from companies who have done the development work and who hold their formulations proprietary.

An early question must be what alloy composition do you seek? Most typically, zinc-nickel plating has a few percent of nickel, say about 6%, chosen for best corrosion resistance ... but is that what you're looking for?

Brenner lists about two dozen formulations but does not claim that they all work; and they deposit varying ratios of zinc to nickel; few supposedly deposit over 90% zinc. Some contain cyanide, which you probably don't want.

His "Bath 6" from Schoch and Hirsch supposedly deposits 96% zinc, and consists of 47 g/l NiSO4.7H20, 20 g/l ZnSO4.7H20, and 22 g/l Al2(SO4)3.
His "Bath 15A" from Sathyanarayana and Rama Char supposedly deposits 93% zinc, and consists of 29.3 g/l Ni and 32.7 g/l Zi as sulfamates, with 16 g/l Na acetate.


Ted Mooney,
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

March 27, 2014

Q. Dear ted mooney,
thanks for your kind reply.
This is my master of science thesis. I want to achieve a coating with below conditions on low carbon steel substrate
1. the nickel wt% is between 8 to 14, and the rest is zinc
2. the deposition technique is pulse plating
3. the temperature is 50 °C
4. pH is 3
5. current density 1 to 100 mA/cm2
6. duty cycle is 5% to 80%
7. we use chloride bath with HCl (for correcting the pH), KCl and H3BO3 acids and ZnCl2 and NiCl2.6H2O

Your help would be appreciated
Thanks & Kindest regards,

mostafa dezfooli [returning]
- Ahvaz, Khuzestan, Iran

March 2014

A. Hi again. I am not a chemist, let alone a zinc-nickel chemist and can't help too much except to say:

- You might try to locate a copy of Brenner's "Electrodeposition of Alloys" in a library (or try to buy one) because it is both the principal authority and the bibliography on the subject. Pages 196-199 briefly list almost 2 dozen formulations for Zinc-Nickel baths, along with their operating conditions; and pages 236-238 list the references where the formulations were found.
- You might also try to get access to, which is a searchable database of patents, journal articles and technical conference proceedings from the metal finishing industry, and includes some references to zinc-nickel plating.
- I would suggest shooting for your midrange current density of 10 ma/cm2, with no pulse plating, and try to get a sound and not black deposit as a starting point before worrying about the percentage of nickel or trying to tame the additional variable of pulse plating. Until you accomplish sound plating of some sort, all the rest should wait. Best of luck.


Ted Mooney,
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

April 17, 2014

A. Anselm Kuhn does a great job with his information resources. I would also recommend two free ways to access information relevant to your query - (the U.S. Patent Office) and The vast majority of available relevant information on zinc-nickel plating is in U.S. Patents. These sites are not difficult to use; they're not easy, either. Both of these sites offer a number of search tools and a researcher would be well-advised to familiarize himself or herself with most of them. Keep in mind a few things - first of all, you cannot 'make, use, or sell' any processes which the patent claims if the patent is still in force (usually 17 years); and secondly, the patentee is required to provide within the text of the patent the 'best mode' of practicing the invention. He or she doesn't have to identify it as such - there is no 'lookie, lookie here is my best mode,' and it is sort of a game to hide it as best can be done.

Having said all of this, if there is no equivalent patent in any country, people in that country are free to practice the teachings of the patent.

Patents can be great, fun reading (in my opinion).

My answer is relevant to many, many other queries.

This is not legal advice; I am not a lawyer. This is just my opinion.

Tom Rochester
Plating Systems & Technologies, Inc.  

Jackson, Michigan, USA

Inconsistent finish of Zinc-Nickel Plating with Yellow Chromate

October 31, 2014

Q. I am facing Quality problems with Zinc Nickel Plating with Yellow Chromate. The Finishing is inconsistent. Please advice on concentration and timing. We are selling Nuts and Bolts. Currently using Chromate Powder.

Paul Netto
Coating Manager - Johor , MALAYSIA

November 2014

A. Hi Paul. We'd all like to help you, but people devote decades of their lives towards solving such problems. Have you called in your zinc-nickel plating process supplier? If you can narrow it down to one particular problem you encounter, and give us your complete plating cycle, we may be able to help. Presumably these nuts & bolts are hardened steel -- can you tell us the grade, etc.? Thanks.


Ted Mooney,
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

November 2, 2014

Q. After Degreasing and Acid Pickling, the studs and nuts (B7/L7) are placed in the Zinc Nickel barrel for approx. 1 hr to obtain thickness above 15 µm. The temp control for the Rectifier is 10-11 amp. Than the nuts and studs are dipped into Nitric Acid, Hot Water, Yellow Chromate solution (90 °C) and Hot Water again before they are blown dry using compressed air. The colour required is Rainbow colour but at times, very dull and rusty.

Paul Netto [returning]
Coating Manager - johor bahru, malaysia

November 6, 2014

A. Obtain your chemical manufacturer's Technical Data Sheets and ensure you are following every detail. Amperage is not temp control. You say your parts are looking dull and rusty. I suspect that's not rust, but a thicker chromate layer which makes the end product look more like a dark orange/brown hexavalent chrome compared to the "rainbow" look you say you're after. Using your vendor's Technical Data Sheet, ensure you have the right concentration, temperature, and time in your chromate tank.

Art Campbell
- OKC Oklahoma

April 19, 2017

Q. I am facing the problem in blackness in fastener plated alkaline zinc nickel.

Arvind Tayal
- Rohtak Haryana

Zinc-Nickel Plating turned dark in 10 days

May 15, 2017

Q. Hi guys, I am noob in Plating, I am working in a plating company in my city and I have a some questions, why the color of plating changed. For example I produced some parts one day, and 10 days after, the color is different? I had light parts with zinc-nickel coverage but later the parts are dark or brown.

Edgar Garcia
- San Luis Potosa, Mexico

May 2017

Hi Edgar. I realize that you admit to being a noobie, but it's still difficult to figure out the cause of a problem that is only verbally described (no pictures) and when we have no process information at all. First question: the parts are presumably chromated; tell us about the chromating step. Thanks.


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

May 26, 2017

Q. Hi Ted, thanks for your answer.

We receive casting from our area of machines, the process is as follows:

Ultrasonic degrease
Hot degrease
Zinc-Nickel Plating (pH 5.2-5.6, Temp 33 °C)

It's the complete process to our product. (Acid Zinc Nickel)

Edgar Garcia [returning]
- San Luis Potosi, Mexico

June 8, 2017

A. Hi Edgar!

As Ted said, please take some pictures of the parts before and after discoloration.

Do you test your plating bath in Hull cell? Does this defect appear in this test too?

Hope we can help you solve this!


Daniel Montanes
TEL - N FERRARIS - Canuelas, Buenos Aires, Argentina

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