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topic 20173

Copper Sulfate Test Method to Verify Zinc Plating?


Q. My company produces car springs and stabilizer bars, approximately 1 million a month. I have been assigned a project to "Verify Zinc Deposition" on our parts. So I am seeking a method to visually see surface coverage of zinc on our parts. I have heard of a test using Copper Sulfate and submersing the parts in this solution for x time and upon retrieval from the solution the Copper Sulfate shows true zinc coverage. I have searched the web seeking an article on this method but cannot seem to find one. Can you offer any web site suggestions or describe this test method more for me so I may try it. We obviously produce components for the Big Three and would like to incorporate a test method in order to give them a warm fuzzy feeling that our zinc plating line is as good as we say it is. I have an SEM in house but would like a more simple test method for our floor operators to preform, as well the SEM can only look at a small portion of the spring I am looking for the entire surface.


Todd S [last name deleted for privacy by Editor]
- Florence, Kentucky

affil. link
Zinc Plating
by Herb Geduld
from Abe Books
info on Amazon


A. The copper sulfate test in not unique to zinc. The copper simply replaces / exchanges for a more reactive metal. XRF would give you a spectrum of the metals present.

Fred Mueller
- Southampton, Pennsylvania, USA


A. Why don't you consider a magnetic thickness tester. It is a nondestructive test and you can check the plating thickness any place you can place a probe. A simple desk top unit is less than $3K. Fischer Technology makes an excellent unit.

Karl Weyermann
- Lebanon, Kentucky, USA


A. Todd -

I would suggest a portable XRF.

Terry Tomt
- Auburn, Washington

Copper sulphate spot test


!! Todd,

Sorry to see that no one answered your question. I am looking for the same information and have had no luck finding any written procedure. Just as you got, everyone seems to have some other idea (maybe relating to a product that they use or sell) but either don't know or aren't willing to say what I need to know. I will give you what little help that I can.

First thing, copper sulfate is very easy and inexpensive to get. It is the blue salt used to kill roots that grow in your plumbing. 32 oz for $6-$7 at Wal-Mart. I have read that you can get it for less, in larger amounts, from farm supply stores. I got the 32 oz one, and due to lack of information, will start to experiment with it soon. Warning this is potentially dangerous stuff. Use caution if you do use it; Protective Gloves [affiliate link to product info on Amazon], apron [affiliate link to product info on Amazon], and Eye Protection [affiliate link to product info on Amazon] along with good ventilation. My need is to test steel, so the test will be different as will the results. I am thinking that a chemistry textbook may be a source of information if all other avenues are dead ends.

Good luck.

Jessie A [last name deleted for privacy by Editor]
- Waukegan, Illinois, USA


thumbs up signHi Jessie. Thanks. But the first answer noted that unfortunately the copper sulphate test would not work in Todd's case, and three people with no vested interests did try to answer his question of how to verify zinc deposition.

Test solutions should start with reagent grade copper sulphate. Using an undocumented concentration of possibly contaminated copper sulphate, intended for use as Root Killer [affiliate link to product info on Amazon], can give your QA department a headache; although there may be uses for garden store copper sulphate in a plating shop, Todd's "Big Three" certainly won't accept the use of Root Killer. There is an ASTM standard for the copper sulphate spot test. Thanks for trying to help, and good luck.

Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha

Ed. note: See entry from Marvin Sevilla re. Preece Test. Apparently Fred and myself are in error, and copper sulphate can be used to verify zinc plating on steel.


A. That ASTM standard would be ASTM A262-13 [affil. link to spec at Techstreet] , copper-copper sulfate test designed primarily to test for ferrite formations in austenitic stainless steel. Enjoy!

Jeff Swayze
- Kelowna, B.C., Canada


A. We use Zinc tracer to detect Zinc contamination on stainless steels. 2/100% Dithizone + 10% NaOH in demineralized water. It turns pink if Zn is present.

Robert R [last name deleted for privacy by Editor]
petrochemical - The Hague, The Netherlands

Recipe for copper sulphate test solution


Q. Can anyone provide the recipe for copper sulphate solution? I found some crystals and someone told me to just mix it with water but weren't sure how much. I need a quick answer and would prefer to cut through the red tape and avoid purchasing the purchasing ASTM A262 test procedure one poster linked to this thread. I need to check some stainless steel mold parts for ferrous content now and also want to use it to determine the presence of chrome or lack thereof on injection blow mold tooling.

Ron Myers
plastics - Jackson, Tennessee USA

February 5, 2008

A. The mixture can be found in ASTM A967 [affil. link to spec at Techstreet] Chemical Passivation for Stainless Steel Parts

4 gm copper sulfate pentahydrate CuSO4.5H20 (we use reagent grade)
250 ml of distilled water
1 ml sulfuric acid H2SO4 (specific gravity 1.84).

Solution is swabbed on part, let stand for 6 minutes minimum part should be carefully rinsed and dried ... if copper deposit is observed then free iron is on the surface of part.

Dennis Cope
- Ontario, California

February 14, 2008

A. I agree with Dennis Cope. I am looking at A967-05 and he has the exact formula and time of exposure. Dennis gets the prize for your question. I am looking at getting lab grade powder of Cupric Sulfate, 500 grams of powder for $15.96 and 90% Sulfuric Acid from in Austin,Texas. They supply mainly to schools.

You can buy copper Sulfate test solution through Stellar Solutions [a supporting advertiser], the makers of Citrisurf. It is $10 for a two ounce bottle, ready made. Good Luck

Ken McElroy
medical - Austin, Texas

September 30, 2009

Q. Does this copper sulphate test solution embrittle high strength steel?

Jo Fortin
- Montreal

Difference between copper sulphate and copper sulphate pentahydrate

April 19, 2014

Q. Hi , actually 2 people did answer Ron's Question, Dennis & Ken and answer it well. They informed him that: 1. Dennis - Copper Sulphate Pentahydrate , 2. Ken - Cupric Sulfate.
... Till I got confused which one is correct among Copper Sulphate Pentahydrate or Cupric Sulfate or both to copper sulphate test solution. Suggest me.

Surya Narayana
Process Engineer - Tumkur , karnataka . INDIA.

April 2014

A. Hi Surya.

Copper Sulphate Pentahydrate or Cupric Sulphate Pentahydrate is the correct long-form of the chemical name. Cupric means copper in oxidation state "+2", which it always is when combined with sulphate, so it doesn't matter whether you say "copper" or "cupric". And "pentahydrate" means that this hydroscopic compound will absorb 5 parts of hydration water if you let it (if you don't seal it away from the air), forming the familiar blue crystals. Copper sulphate is just a short form which people understand to mean cupric sulphate pentahydrate: CuSO4 · 5H2O

Good luck.


Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha

January 9, 2016

A. Such test exist the name of the test is The Preece test.

Here is a quote from the PDF file I was able to find.

"The Preece test is applied by dipping the zinc-coated article, which has previously been cleaned from grease or other foreign material, into a "neutral" solution of copper sulphate of a specified concentration (1.27 mole). This concentration is usually denned by its specific gravity (1.186 at 18 °C), and the solution is maintained at a temperature of 18 °C during the test. (6) The sample is immersed in the solution for 1 minute, removed, washed in running water, and freed from the loosely precipitated copper by light rubbing. The 1-minute immersions and cleanings are repeated until an endpoint is obtained in the form of a bright adherent deposit of copper. This indicates that the iron has been exposed there. The number of immersions (dips) reported for each sample is one less than that required for the appearance of adherent copper"

here is the PDF with Plenty of detailed information

Marvin Sevilla
- Managua, Nicaragua

November 7, 2017

A. The modern form of the Preece Test seems to be ASTM A239 [affil. link to spec at Techstreet].

Do not refer to ASTM A967 or A262 as referenced above, those are different formulations of copper sulfate used for entirely different tests on stainless steel.

Thanks to Marvin Sevilla for identifying this one for us.

ASTM A90 [affil. link to spec at Techstreet] also seems to be relevant to people who need to confirm the quality of a zinc coating over steel.

ray kremer
Ray Kremer
Stellar Solutions, Inc.
supporting advertiser
McHenry, Illinois
stellar solutions banner

November 9, 2017

A. ASTM A239 [affil. link to spec at Techstreet] is entitled "Standard Practice for Locating the Thinnest Spot in a Zinc (Galvanized) Coating on Iron or Steel Articles." That's all it is. The Preece Test used to be an acceptable method for crudely estimating the coating weight, but now the consensus, as noted in this practice under X3 is "... this practice cannot be used for determining the weight of the zinc coating ..." There are many, many excellent tests for the determining the thickness of zinc on steel.

Tom Rochester
Plating Systems & Technologies, Inc.  
supporting advertiser
Jackson, Michigan, USA
plating systems & technologies banner ad

October 24, 2019

Q. I have a steel part that has been zinc plated but looks more like it has been DA sanded. I want to test the part to see if it has in fact been zinc plated. I bought some Copper sulfate and wanted to know how much water to mix with it to test and if those are the only 2 items I would need to test this. Any thoughts?

Chris Springer
- Hamilton Indiana

October 2019

A. Hi Chris. In high school you may have seen the experiment where an iron nail placed in blue copper sulphate gets an orange copper coating. Despite Marvin's mention of Preece test, trying to prove the presence (let alone quality) of zinc plating on a steel part seems doubtful if you are inexperienced and not using laboratory grade equipment.

Considering that zinc plating will not function correctly without chromate conversion coating, and that you apparently have no history about the surface finishing of this part, and that the test will not tell you the thickness or suitability, the question becomes "why do you care?". Tell us a bit about what's going on please.


pic of Ted Mooney
Ted Mooney, P.E. RET - Pine Beach, New Jersey
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