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"Problem of white spots after Zinc Plating"

Current question:

White Patches observed 4-5 days after Alkaline Zinc Plating (Cr6 Free)

October 21, 2020 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Our components after alkaline zinc plating (Cr6 Free + Top Coat) are having white patches after 4-5 days even though the components are not exposed to environmental conditions in our plating shop, i.e., each component was packed with plastic cover separately and stored. Now that we are observing white patches on the component. Can anyone explain the reason?

Digvijay Bhosale
- Kolhapur, Maharashtra.

October 22, 2020

A. You are probably not neutralizing off the strong alkali from the alkaline zinc. Use a 1/4%/vol Nitric Acid between the plating and the chromate.

robert probert

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

September 8, 2021

A. Please make sure that you can store your finished product at humidity [not] more than 90.
Do not pack you material immediately as after spin dry; there will be a chance of retaining moisture which may act as a SST chamber when you pack your finished product immediately in PP bags

Rahul VP
- Pune Maharashtra

August 2, 2021

Q. Our components after alkaline zinc plating and black coating are having white patches after 4-5 days even though the components are not exposed to environmental conditions in our plating shop, i.e., each component was packed with plastic cover separately and stored. Now that we are observing white patches on the component. Can anyone explain the reason?


August 2021

A. Hi Ankit. You copied & pasted Digvijay Bhosale's question, but you have offered no comment to Robert Probert's answer to it. I hope I'm not overly judge-y but that seems kind of silly :-)

Please do us a favor and comment on Mr. Probert's proposed solution. Thanks!

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey

Closely related historical postings, oldest first:


Q. Dear Sir,

We are observing a problem of white spots after zinc plating. Can you please tell a solution for this problem? Thanking You, Yours Truly,

Pune , Maharashtra , India


Q. We are also facing similar problems occasionally. Answer to this question will help us also.


Sonu S Andrews
- Chennai, TN, India

affil. link
Zinc Plating
by Herb Geduld
from Abe Books


A. I am guessing that the white spots you are referring to is actually white rust, which means that the zinc layer has been corroded. If this happens right after plating, maybe the problem lies in the drying process (not completely dried up), leaving droplets of water on the surface of the plated parts. Other possibilities might be from poor final rinsing and poor chromate dip.

Hartarto Ciputra
- Surabaya, Indonesia


A. This is the common problem in White zinc. The most possible problems are in water rinses after plating & yellow passivation. First these things should be controlled. Secondly drying of the components is very important factor. Please look into that also. Very rarely there can be the problem of contaminations in the plating tank, which can be sorted out by various treatment you must be doing in your normal cleaning times. Please try & let me know.



? Dear sir,

Before we attempt to answer your query, it is very important to know what base metal are you plating? What is the pretreatment sequence? What type of zinc plating are you doing? Lastly where does the white spot occur i.e., HCD, lcd or random? Above will give better insight into the problem.

G.S. Sharma
- India

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 :-)

Non-Cyanide Zinc Plating Problem

January 9, 2009

Q. White patches seen after trivalent blue / yellow passivation in non-cyanide/alkaline zinc plating process. Please tell me that what will be root causes starting from degreasing to passivation.

Nitin Kapare
Plating Chemical Supplier - Pune, Maharashtra & India

January 14, 2009

A. Hi Nitin,

Do you observe the white patches after the passivations, cos many a times when the passivations parameters, like the ph, time, are not set it gives such appearance, secondly if you have a electrocleaner in the line for non cyanide zinc is preferable , cos the cleaning of components I quite important in case of non cyanide zinc, did you check the hull cell for the working bath , do you observe any white patches and at last it have the zinc dissolution tank and are you maintaining the zinc content very well in the bath.

praveen kumar
Praveen Kumar
    plating process supplier
Mumbai, India


January 29, 2009

A. Is usually due to the hardness of the water and remove additives patent provider additives.

Oscar Villaobos
chemical supplier - Guadalajara, Jalisco, Mexico

February 24, 2009

A. Check the Nitric Dip (activation prior to passivation).

With alkaline zinc you may need a strong (minimum 1% by volume) Nitric Acid Dip prior to passivation.

There can be many causes for patches, etc... but this seems to be the most common cause.

Thomas E. Kidd
- Budapest, Hungary

September 26, 2012

Q. Our components after alkaline zinc plating are having white patches after 20 days even though the components are not exposed to environmental conditions in our plating shop, i.e., each component was packed with plastic cover separately and stored for 20 days. Now that we are observing white patches on the component, can any one explain the reason?

Raghavendra BN
- Bangalore, Karnataka, India

October 1, 2012

A. Dear Mr. Raghavendra,

I think you are experiencing this because of a bad or absent chromating of the zinc plated parts. The white patches are zinc oxidation/corrosion. Zinc corrodes in air, so you must apply a chromate (hexavalent or trivalent, according to spec) conversion coating so it does not corrode a few days later.

Hope this can solve your issue, best regards!

Daniel Montanes
fasteners manufacturer - Cañuelas, Buenos Aires, Argentina

October 10, 2012

A. The area of post water swill (even pre and post chromating) and a final hot water swill may be helpful. Packing inside plastic bag should be after proper drying.

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

July 29, 2020

Q. Hello sir,

We are observing white patches right after zinc plating.

Bhaktesh Naik
- bangalore peenya, India

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