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topic 30658

How Does Copper Sulfate Test for Passivation Work?

adv.    koslow passivation test kit

A discussion started in 2004 but continuing through 2017


Q. Dear Readers,

I have heard that a way to check for iron on the surface of a passivated stainless steel part is with the copper sulfate test. From what I can gather the copper replaces the iron due to the fact that the iron is more easily oxidized. Chromium is more easily oxidized than iron, so why doesn't the copper also replace the chromium?

Thanks for your input.

Shaun C [last name deleted for privacy by Editor]
manufacturing w/ in-house plating - Sheridan, Indiana


A. Chromium and nickel will not be replaced with the Copper sulfate test solution (which also contains sulfuric acid), only the Fe or other less noble metals. If there is free iron on the surface it will be replaced by the copper, forming the distinctive copper color on the surface in this 6 minute test.

Of course, this test should only be used on austenitic stainless steel. Some people use it on other grades, but you can get false failures.

lee kremer
kremer signature
Lee Kremer
Stellar Solutions, Inc.
supporting advertiser
McHenry, Illinois
stellar solutions banner


Q. Why is it that Fe is less noble than Chromium? From their locations it appears that Iron is more noble.

Chris L [last name deleted for privacy by Editor]
co-op/manufacturing engineering - Sharon, Massachusetts

A. Hi Chris. It's possible that you are misinterpreting the chart. Platinum and Gold are on the noble end of the seawater series, magnesium is on the active end. Nickel and chromium are closer to platinum than steel is.


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

April 16, 2008

Q. I need to determine effectiveness (pass/fail) of an up-coming passivation procedure. I have read that using copper sulfate is a proper method, however, I have not found a test kit, only the copper sulfate itself. How do I go about constructing a procedure or test method?

John Stiglbauer
- Columbia, South Carolina

May 4, 2008

A. To answer John's question, I'd look up a standard test and use that, rather than make my own. Primarily because I'm lazy, but you can also argue that something published by a known organization probably has had some thought behind it, maybe it's been vetted as well.

So I'd go to Assist Quicksearch by typing that into Google and hitting "I'm feeling lucky". Then I'd type "753" into the number box, and click on the icon that will display Mil-STD-202, Method 101 [link is to free spec at Defense Logistics Agency,] revision C [replaced by AMS-STD-753 [link by ed. to spec at TechStreet]]. Then I'd read that one, and if it met my needs, I'd use it.

lee gearhart
Lee Gearhart

April 2, 2009

Q. Once or twice a year my company use copper sulfate to check for surface free iron on 300 series stainless steel.
The copper sulfate [linked by editor to product info at Amazon] is in powder (crystal) form that is made into a solution.
We misplaced the instructions on how to make the solution.
What is the proper way to test for surface free iron and how is the solution made?

Thank you,

Bob Hildebrand
material fabricator - West Islip, New York

June 23, 2009

A. If you need instructions / information look up ASTM A380 [link is to the practice at TechStreet] section7.2.5.3 Copper Sulfate Test.

A company that makes and sells kits for this is Koslow Scientific Company in Englewood, New Jersey.

Francisco Robles
- Denver, Colorado USA

July 24, 2012

A. Copper sulfate solution is a saturated solution. It should be kept fresh.
Be sure to carefully remove all of the copper deposits. This is a slightly destructive process.
Koslow Scientific company sells a color spot test kit that does not require any mixing of chemicals. It is called the Passivation Color Kit 1626. The color reaction takes place not on the metal surface but on a sensitive test paper.

Gary Huller
Koslow Scientific Company
supporting advertiser  
Englewood, New Jersey
koslow banner

June 7, 2015

Q. What is the aim of the copper sulfate test in martensitic stainless steel used in dental hand instruments? What is it testing?

Dr.Hany Elwahsh
Acrostone - Cairo, Egypt

January 11, 2016

Q. Is it a requirement to be an A2LA certified to perform a passivation test for Stainless Steel?

Randy Phillips
- Richfield, Wisconsin, USA

January 2016

thumbs up sign Hi Randy. It's an interesting question, but I'm not sure that it's worded quite clearly enough.

I should think that anyone who can safely perform a passivation test is welcome to perform one, but that we can't put much credence in their results if we don't have reason to trust their qualifications :-)

Can we have the situation? Thanks!


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

January 11, 2016

A. Randy,
The question is, is it a requirement by whom? The ASTM and SAE standards on passivation don't say anything about certification. If your customer asks for A2LA though, then you need to have it.

ray kremer
Ray Kremer
Stellar Solutions, Inc.
McHenry, Illinois

Remove copper deposit after stainless passivation testing

September 12, 2016

Q. After performing the copper sulfate test, which might be the best way to get rid of the copper deposits on the SS surface.

Angel Espinosa
electronics - Swindon UK

September 12, 2016

A. Good day Angel.

If you are passivating in the nitric based solutions, give the parts a dip in the passivating solution. Keep this solution off line for this purpose only, to avoid contaminating the process solution with copper.


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

simultaneous September 12, 2016

A. Angel

Your question implies that the test parts failed. Dial in your passivation process and you won't have deposited copper to remove.

Willie Alexander
- Green Mountain Falls, Colorado

September 13, 2016

Q. Hi Eric,

Thanks for the reply. I am planning to perform the test during maintenance activities after cleaning the plates. Is there a way to remove the copper deposits without dipping? Thanks again. Angel

Angel Espinosa [returning]
electronics - Swindon UK

September 13, 2016

A. Angel,
Sodium persulfate with a little bit of acid in it makes a good copper stripper that isn't very hazardous to work with.

ray kremer
Ray Kremer
Stellar Solutions, Inc.
McHenry, Illinois

November 8, 2017

Q. I have some parts (stainless steel) that they have already been chrome plated or electropolished. My question is, after passivation, do I have to perform the Copper Sulfate test on those parts which already been chrome plated?

John Zhou
Medical Device Manufacturer - West Hills, California, USA

November 10, 2017

A. We've talked already about this, but I will answer here also for the benefit of other readers.

First I will note that chrome plating and electropolishing are very different things.

Chrome plating is not normally done with stainless, and if it is, I see no reason to passivate or run a passivation test because the stainless has been covered over. Copper sulfate is often used to check for gaps in plating over carbon steel though.

Electropolished stainless can be citric passivated for extra good corrosion resistance, at which point it's certainly fine to run copper sulfate testing in order to comply with the relevant standards. If you don't have to comply with the standards, then it's pretty much up to you.

ray kremer
Ray Kremer
Stellar Solutions, Inc.
McHenry, Illinois

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