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Analyze Chrome Plating Bath; Determine sulphates

Q. Sir,
As I joined newly a chrome plant,
Please provide me the link or something by which I can check concentration of Cr2O4 and H2SO4 and how to set current density in bath and maintain smooth working of process

Anil Chauhan
Employee - Dammam, Saudi Arabia
June 4, 2022

June 2022

A. Hi Anil. We appended your inquiry to one of our threads on the subject.
Current density is more difficult. Never less that 1 Amp per square inch, usually 50 to 100% more, although even higher in some cases.

How to "maintain smooth working of process" is the subject of large books, it's not something that can be fully dispatched here ... but give an example of a single problem and readers will be able to tell you how to avoid it :-)

Luck & Regards,

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

⇩ Related postings, oldest first ⇩


Q. Dear Sirs,

We would really appreciate if you could help us on the following problem which we are facing in our labs ( Hellenic Aerospace Industry - Physical Science Labs):

In our labs we have to determine Sulfuric Acid in Chromium plating bath.The limits for Chromic Acid in the bath is 225-270 gr/l and for Sulfuric Acid is 2.25-2.70 gr/l (a very small concentration range of 2.70 - 2.25 = 0.45 g/l) . We tried two methods for the determination of Sulfuric Acid in the solution but taking into account the very small limits range of Sulfuric Acid in the solution and the time the methods need, we are not satisfied by the results of both methods

More specifically:

A. The first (titration) method is as follows:

In above method (A), a difference of 0.1 ml of 0.1 Magnesium Chloride (titrant) results in a deviation of result equal to 0.1 gr/l Sulfuric Acid (that is, a very high deviation of approximately 22% in comparison with the very small limits range of 0.45 g/l of Sulfuric Acid).

B. The second (weighing) method is as follows:

In above method (B) we face the difficulty to clean up the filter from the Chromium during filtration. Additionally a small difference of 0.002 gr in weighing gives a deviation of result equal to 0.084 gr/l of Sulfuric Acid ( that is, again a very high deviation of approximately 19% in comparison with the very small limits range of 0.45 g/l of Sulfuric Acid).

We tried to perform above analyses using a higher quantity of sample to eliminate the error, but we faced difficulty during the reduction of Chromium due to rapid expansion (explosion) of the solution during the reaction.

Angela Nikolaou
aerospace - Tanagra, Viotia, Greece

"Hard Chromium plating"
by Robert K. Guffie

on AbeBooks

or Amazon

(currently UTL on eBay)

(affil links)

"Chromium VI Handbook"
by Guertin, Jacobs, Avakian

on AbeBooks

or eBay or


(affil links)

"Chrome Plating Simplified"
by Clarence H. Peger
(You're unlikely to find this for sale ... but copies are in select libraries)
from AbeBooks
** rarely available **

or eBay
** rarely available ** or

** rarely available **

(affil links)

simultaneous replies

A. I think that you have set your limits tighter than necessary. Chrome is constantly depleting with plating. sulphate is only lost to drag out, so the ratio is constantly changing throughout the day.

The Kocour centrifuge method is fairly quick, simple, reasonably repeatable and more than accurate for chrome plating needs. Use the electric centrifuge and not the hand one. If you like, you can do a correlation of the centrifuge method and your lab method as well as samples from reagent grade materials to establish a correction factor if you really think that it is required. My centrifuge tubes were calibrated in oz rather than grams. They may offer one in grams, but if not it is a very simple conversion. I am a chemist and truly appreciated this adequate method.

James Watts
- Navarre, Florida

A. My method of choice would be (b). That's the standard accepted method. I do not know that barium sulphate would completely dissolve even in a solution containing EDTA, as it is notoriously insoluble in just about anything. If you are determined to avoid the gravimetric method, it might work to fuse the recovered barium sulphate with sodium carbonate / washing soda [affil links], dissolve the melt in dilute nitric acid, then adjust the pH to about 10 with ammonium hydroxide. The EDTA could then be added, then titrated away with your standard magnesium solution.

If I were you, I would just do the gravimetry. The boiling over you describe can be avoided by adding the ethanol slowly to the mixture, and heating it gradually. And, it is not necessary to ignite the precipitate. It is good enough to filter it with a Gooch crucible and glass filter mat and dry it at 105 °C.

dave wichern
Dave Wichern
Consultant - The Bronx, New York

simultaneous replies

A. A quick and easy way to measure sulphate is precipitation with barium chloride, then centrifuge and measure volume of precipitate. Kocour company makes a centrifuge and graduated tubes for this purpose. it is quite accurate.

jeffrey holmes
Jeffrey Holmes, CEF
Spartanburg, South Carolina

A. GO FOR IC TECHNIQUES IT CAN DETERMINE sulphateS TO ppm levels. Otherwise the techniques you use are the ones commonly used in industry. TRY KOCOUR sulphate testing kits .

vikram dogra
Vikram Dogra
Irusha India - Chandigarh, India

A. 1. The deviation is not much of a problem. There is little or no difference in performance of the chromium plating solution with the small error in the analysis. To do a simple analysis, Kokour Co. provides a Kit that includes a centrifuge that runs at a specified RPM The procedure is simple and quick and may even be more precise than the ones you have mentioned. sulphate is precipitated by a barium salt in a centrifuge tube with a small diameter tip that is calibrated. Simply read the number after centrifuging.

don baudrand
Don Baudrand
Consultant - Poulsbo, Washington
(Don is co-author of "Plating on Plastics" [on Amazon or AbeBooks affil links]
           and "Plating ABS Plastics" [on Amazon or eBay or AbeBooks affil links])


Q. Thank you all very much for responding. Here are some very questions and comments

1. Could I have some info as concerns the supply of the Kocour Kit? Could you describe briefly, what the kit consists of. Is any "Kocour solution" included in the kit and what is it exactly?

2. Have in mind that the hexavalent Chrome must be reduced to trivalent, otherwise insoluble Barium Chromate would form along with the sulphate.

3. The sulphate limits are really tight, but this is because of our clients' specifications.

4. Do you think that the 19-20% deviation in the sulphate determination is a small one?

4. The precipitate has to be ignited at 600 °C because it holds water strongly, as it is suggested in the Electroplaters' Process Control Handbook [on on Amazon (adv.)], edited by Gardner Foulke.

Thanks again,


Angela Nikolaou [returning]
aerospace - Tanagra, Viotia, Greece

simultaneous replies

A. The kit comes with 2 solutions, the centrifuge of choice and special centrifuge vials.You can get the desired information from Kocour or your plating supply vendor.

As far as the accuracy of the kit, I will hazard a guess that over 95% of chrome platers use that method as it is sufficiently accurate to maintain a 100:1 plating solution.As I said in my first post, the ratio is constantly changing and it is the ratio that is important.

James Watts
- Navarre, Florida

Q. Hi again, Please give me the address, web site, fax and/or e-mail of Kocour company, to come in contact with. I tried the web site [but it didn't work].


Angela Nikolaou [returning]
aerospace - Tanagra, Viotia, Greece

Their URL is, Angela.
Update Dec. 2019: That link doesn't work any more either. Please remind them that lacking presence on the world's most popular finishing website, and making you wait until their competitors get around to providing you their updated contact info makes things hard for you :-)

A. If you use the Kocour method and want very accurate results, you will want to calibrate the tubes yourself against a prepared 100:1 chromic/sulphate standard. You will find that you will need to apply your own correction factor to most tubes. Repeat the calibration every three months on each tube. This will account for interior scratches that tend to occur with use and cleaning.

Jon Barrows
Jon Barrows, MSF, EHSSC
GOAD Company
supporting advertiser
Independence, Missouri

Q. Dear all
I've heard that there is a centrifuge method for determining sulphate concentration in chrome plating solution. However, I don't know how it works and what shall I do. I'll be grateful if anybody could advise.


Sani [last name deleted for privacy by Editor]
- London, UK

Multiple threads merged: please forgive chronology errors :-)

Q. We are having Chrome plating plant, for which we measure the temperature and the density of the bath to control the process. However we wish to do a monthly analysis of the bath to ensure everything is OK. Please let us know what the elements to be checked and the method of analysis.



A. George,

I hope you have a excellent supplier for your hard chrome solution. The people here at this forum can't not give you the right answer for your hard chrome supplier:). But I like to get a analysis of this, trivalent chrome, sulfuric acid ratio to chrome, iron, copper, and if you use a SRHS Chrome the content's of fluoric silicate.


Anders Sundman
Anders Sundman
4th Generation Surface Engineering
Consultant - Arvika,



You must weekly not monthly make a chemical analysis for your tank and add the chemical compounds if the tank needs that . In chemical analysis you must check chromic acid content and sulfuric acid content and the ratio between chromic acid and sulfuric acid . About the method of chemical analysis you can ask your chemical suppler to give you the data sheet . Also you can daily check the (Be) baumé (it is hygrometer scale for density) for the solution in the tank and compare it to the standard point.

Aly Gomaa
- Cairo, Egypt

A. Dear George,

You must check chromic and sulfuric acid content, baumé, trivalent chrome and most common impurities (iron, copper, zinc,etc.).


Christos Sigalas
- Athens, Greece

Quick Analysis of Chrome Bath

Q. Is there a procedure available for checking Cr +6, Cr + 3 in chrome bath using spectrophotometer? What is the wave length at which one can detect Chrome?

Kaushik Magiawala
plating shop employee - Gandhinagar, India

A. You may want to get the book Colorimetric Analsis of Metal Finishing Solutions ..." [on Amazon, AbeBooks (adv.)] by Aubrey Knowles that will describe various methods. If not, you can try a simple direct method with hex chrome at 370nm and tri chrome at 640 nm. Dissolved iron will likely interfere with the hex chrome measurement, but it may be accurate enough for your purposes.

Jon Barrows
Jon Barrows, MSF, EHSSC
GOAD Company
supporting advertiser
Independence, Missouri

A. The Kocour test is easy and very accurate. Repeatable if you follow the steps accurately. I personally have used it 16 years off and on as they had some others testing the baths over the years. Our company has used it for 20 something years and our tanks stay optimum.

I put the entire testing process on my site, here is the link. Hope it helps:

Rodney Stephens
industrial plating - Anniston, Alabama
May 19, 2009

Ed. note: Sorry readers, that link is broken :-(

Most links break in a few months or years, making them difficult to maintain across our quarter million postings. If you provide a link, please give title & author or other info so we have a fighting chance to fix broken links. But we urge you to put your stuff directly here (we have all the room in the world) rather than at a link that will almost surely soon fail :-)
We thank Rodney for his input, but we heard the librarian whisper that he's on her "naughty" list for ripping out and swallowing a page of this reference work :-)

⇦ (tip: readers usually show little interest in abstract questions,
but your actual situation will usually bring responses
)   smiley face

Q. Can anyone can send the procedure for solution analysis of chrome.

I would like to check - Chromic acid, sulphate, iron value.

Ramesh VS
employee - Chennai, Tamil Nadu, India
June 2, 2010

Q. I determine the concentration of sulfuric acid in chromium bath using a centrifuge using HCl and barium chloride 20% .
I need another way to determine the concentration of sulfuric acid in chromium bath other than centrifuge.

Thanks in advance.

Hanan Fathy
- Egypt Cairo
July 4, 2021

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