Spot test to Verify Zinc Plating. ASTM A239 / Preece Test / Copper sulphate

A. Check the Advanced Knowledge Technologies department at the University of Aberdeen (Scotland). Professor Alun Preece is one of those involved with that project. This is the only reference that appears close, but you did not indicate the type of process or material you were needing to test - sorry.

A. Preece test is the following ASTM test:

A191- Discontinued 1942: Test Method for Uniformity of CoatIng by the Preece Test (copper sulphate ⇦ this on eBay or Amazon [affil links] Dip) on Zinc-Coated (Galvanized) Iron or Steel Articles.
Replaced byASTM A239.

A. Test still appears as referenced standard for items galvanized. See for example kortick.com catalog references to hot galvanized hardware they make. Others also cite so - it is still alive and well either as shorthand for current standards or still employed as original.

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Editor's update Aug 2020: "Preece" no longer seems to appear in that kortick.com catalog.

"Zinc Plating"
by Herb Geduld

on AbeBooks

or eBay or

Amazon

(affil links)

A. The copper sulphate 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.

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.

A. Todd -

I would suggest a portable XRF.

!! 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 sulphate 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 hardware and big box stores. 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; rubber gloves ⇦ this on eBay or Amazon [affil links] , apron ⇦ this on eBay or Amazon [affil links] , and Eye Protection [affil links] 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.

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Thanks Jessie. But the first reply to Todd (from a very highly experienced Past President of the American Electroplaters society, not someone with a vested interest) expressed concern whether a quick & simple copper sulphate test by line operators could work in Todd's case, and he explained why (it reacts with bare steel as well as with zinc); and two others with no vested interest also tried to answer his question of how to best achieve his goal.
If someone asks what candy bars they should eat because the doctor told them they need more protein, suggestions that they eat meat or beans instead is not quite "no one answered" -- let alone justification to assert that their attempts to help might be "related to a product they sell" :-)

There may be uses for garden store copper sulphate in a plating shop, so we appreciate the advice on inexpensive sources, but Todd's "Big Three" may not get a "warm and fuzzy feeling" about the commitment to quality of a shop that uses Root Killer instead of reagent quality chemicals. Thanks for the help, and good luck with your experiments!

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2003

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A. copper sulphate can distinguish zinc from cold rolled steel. We have successfully used it in a bore analysis test to measure zinc coating weight on galvanized sheet. The copper turns zinc black and iron a copper colour.

Stan S.
Metal Research - Hamilton, Ontario
January 26, 2022

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Editor's update: See entry from Marvin Sevilla re. Preece Test below.

A. That ASTM standard would be ASTM A262, copper sulphate test designed primarily to test for ferrite formations in austenitic stainless steel. Enjoy!

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.

A. Dear Chris :
Peace be upon you,

5% copper sulphate CuSO4 is a good solution for that, where it forms black color with zinc and red with steel.

Best Regards

A. The mixture can be found in ASTM A967 Chemical Passivation for Stainless Steel Parts

4 gm copper sulphate 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.

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 sulphate, 500 grams of powder for $15.96 and 90% Sulfuric Acid from Sciencestuff.com in Austin,Texas. They supply mainly to schools.

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

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!

Regards,

A. Such test exists; the name of the test is The Preece test.

Here is a quote from a 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
http://nvlpubs.nist.gov/nistpubs/jres/12/jresv12n6p785_A2b.pdf

XRF Coating Thickness Analyzer

on eBay or

Amazon

(affil links)

Thanks for the knowledge you have shared with us on so many threads, Marvin! You're broad experience is amazing. Even still, in this particular case I tend to agree with the other responders that methods like X-Ray Fluorescence (which didn't exist when that paper was written in 1934) may be more practical. Thanks again for the resources you bring to this site.

Luck & Regards,

A. The modern form of the Preece Test seems to be ASTM A239.

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

Thanks to Marvin Sevilla for identifying this one for us.

ASTM A90 also seems to be relevant to people who need to confirm the quality of a zinc coating over steel.

A. ASTM A239 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.

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. So trying to prove the presence (let alone quality) of zinc plating on a steel part with copper sulphate seems doubtful if you are inexperienced in chemistry and not using laboratory grade equipment. But Marvin has listed the URL of the relevant reference which you can consult.

Considering that zinc plating will not function correctly without a chromate conversion coating, and that you apparently haven't been told the history of the part in question, and that this test will not tell you the thickness or suitability, I'm intrigued with why you are asking. Tell us a bit about what's going on please.

Thanks & Regards,

A. Dear Silvio Grando,

Look this up:

https://pubs.acs.org/doi/pdf/10.1021/ie50028a009

It might help you in the right direction; it seems the test is susceptible for many parameters. (I have "0" experience with it.)

Also if you type in "hot dip galvanizing" in google or at the website of a well-known large store that started as a online bookstore, there are lots of resources available. Order a few. If you're new in the field, a painful process. Sometimes paying a consultant is worth the money.

Good Luck,

Harry.