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Chemists? NO picture but the experts shoud know.

I have a twenty year old Alligator key fob with brass snaps. There is a thick green scum around the snaps where it touches the leather. A friend has lincoln cents in her dad's blue folder with the same gren scum. What is the chemical name of the green scum? Copper___________? It comes off easily (if not too thick) with a toothpick or acetone. Thanks in advance!

PS How would a chemist write the reaction? XX + XX... = XX

Comments

  • DeplorableDanDeplorableDan Posts: 2,474 ✭✭✭✭✭

    Verdigris?

  • CaptHenwayCaptHenway Posts: 31,436 ✭✭✭✭✭

    Commonly called verdigris, though I think there are several forms of verdigris.

    Numismatist. 50 year member ANA. Winner of four ANA Heath Literary Awards; three Wayte and Olga Raymond Literary Awards; Numismatist of the Year Award 2009, and Lifetime Achievement Award 2020. Winner numerous NLG Literary Awards.
  • jmski52jmski52 Posts: 22,263 ✭✭✭✭✭

    Copper sulfate

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  • lkeneficlkenefic Posts: 7,617 ✭✭✭✭✭

    Copper sulfates (CuSO4) are usually blue when purified in crystalline form, but will likely be seen as green when still on the substrate (the copper coin).

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  • jonathanbjonathanb Posts: 3,386 ✭✭✭✭✭

    Copper chloride is the simplest guess. Chlorides are available all over the place, including sweat, etc.

    The real answer is that you've probably got a mixture with all sorts of stuff contributing.

  • BarberianBarberian Posts: 2,883 ✭✭✭✭✭
    edited February 1, 2024 1:03PM

    My understanding is hydrochloric acid (HCl) is a by-product in PVC polymerization and needs to be neutralized during manufacture. I figured the green salts formed on coins might be cupric chloride from residual HCl.

    Here are some cupric salt crystals and the light corrosion spots often associated with them on a top pop CC coin.

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  • ShamikaShamika Posts: 18,758 ✭✭✭✭

    The simply answer is that verdigris is not necessarily just one molecular compound. It is usually a combination of copper sulfides, chlorides, and oxides.

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  • silviosisilviosi Posts: 444 ✭✭✭

    Interesting question because is not only one kind of Verdigris.

    Composition and Properties of Verdigris
    Verdigris is not a unique chemical substance but is a collective name for various copper acetates. Their color varies from blue to green.

    It reacts with binding media such as oils and resins and forms transparent oleates or resinates. This property has been utilized for preparing transparent green glazes called copper resinates by dissolving verdigris in warm turpentine resin mixed with mastic and wax.

    Neutral verdigris is neutral copper acetate with the formula Cu(CH3COO)2·H2O. It can be prepared by solving basic verdigris in acetic acid.

    **Basic verdigris **can contain several forms of copper acetates such as [Cu(CH3COO)2]2·Cu(OH)2·5 H2O or Cu(CH3COO)2·Cu(OH)2·5 H2O which are both blue. The following copper acetate shows green color: Cu(CH3COO)2·[Cu(OH)2]3·2 H2O.

    The pigment, in general, is not very stable and decomposes on heating, they are soluble in dilute acids and react with alkalis forming copper hydroxide.

    **Origins: name **vert de Grice green of Greece ,Old French vere grez  Middle English vertegrez

    **Types: **
    1.  consisting principally of basic copper sulfate.
    2. a green or bluish patina formed on copper, brass, or bronze and consisting of a basic salt of copper containing both copper oxide and a copper salt
    3. a green or blue crystalline substance obtained by the action of acetic acid on copper and used as a fungicide and pigment; basic copper acetate

    For those interested: XRF Spectrum in the Free XRF Spectroscopy Database of Pigments Checker, CHSOS website.
    https://chsopensource.org/verdigris-k-44450/

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  • Married2CoinsMarried2Coins Posts: 136 ✭✭✭

    @Barberian said:
    My understanding is hydrochloric acid (HCl) is a by-product in PVC polymerization and needs to be neutralized during manufacture. I figured the green salts formed on coins might be cupric chloride from residual HCl.

    Here are some cupric salt crystals and the light corrosion spots often associated with them on a top pop CC coin.

    I am not a chemist; however:

    1. The green crude in the wing looks exactly like the sludge on the copper.
    2. I suspect that the stuff on silver has a different chemical composition than the sludg found on copper.
  • Married2CoinsMarried2Coins Posts: 136 ✭✭✭

    @Shamika said:
    The simply answer is that verdigris is not necessarily just one molecular compound. It is usually a combination of copper sulfides, chlorides, and oxides.

    I was under the impression that "verdigris" is a "catch word" for several compounds. It is like the "xerox" for every SOFT, GREEN, CHEMICAL REACTION RESIDUE. Is this correct?

  • Married2CoinsMarried2Coins Posts: 136 ✭✭✭

    @silviosi said:
    Interesting question because is not only one kind of Verdigris.

    Composition and Properties of Verdigris
    Verdigris is not a unique chemical substance but is a collective name for various copper acetates. Their color varies from blue to green.

    It reacts with binding media such as oils and resins and forms transparent oleates or resinates. This property has been utilized for preparing transparent green glazes called copper resinates by dissolving verdigris in warm turpentine resin mixed with mastic and wax.

    Neutral verdigris is neutral copper acetate with the formula Cu(CH3COO)2·H2O. It can be prepared by solving basic verdigris in acetic acid.

    **Basic verdigris **can contain several forms of copper acetates such as [Cu(CH3COO)2]2·Cu(OH)2·5 H2O or Cu(CH3COO)2·Cu(OH)2·5 H2O which are both blue. The following copper acetate shows green color: Cu(CH3COO)2·[Cu(OH)2]3·2 H2O.

    The pigment, in general, is not very stable and decomposes on heating, they are soluble in dilute acids and react with alkalis forming copper hydroxide.

    **Origins: name **vert de Grice green of Greece ,Old French vere grez  Middle English vertegrez

    **Types: **
    1.  consisting principally of basic copper sulfate.
    2. a green or bluish patina formed on copper, brass, or bronze and consisting of a basic salt of copper containing both copper oxide and a copper salt
    3. a green or blue crystalline substance obtained by the action of acetic acid on copper and used as a fungicide and pigment; basic copper acetate

    For those interested: XRF Spectrum in the Free XRF Spectroscopy Database of Pigments Checker, CHSOS website.
    https://chsopensource.org/verdigris-k-44450/

    g

    I have a bad habit of starting at the top of a thread and posting more questions and opinions before reading everything first. I think all the info I need will be in your post. Thanks. Now I need to digest it!

  • SapyxSapyx Posts: 1,960 ✭✭✭✭✭

    The verdigris that forms on coins is not copper acetate - at least, it won't be unless your coins are stored with jars of vinegar. The pale green paint pigment also known as "verdigris" is made from copper acetate. Same word, different contexts - and different compositions.

    Exactly what the "green scum" that forms is made of, is dependent on which acid did the corroding. Hydrochloric acid will give copper chloride, sulfuric acid will give copper sulfate, that sort of thing. Copper has complex chemistry, and "a coin corroding" is a real-world scenario, with complex and competing chemistries occurring simultaneously - it's not a single neat chemical reaction like you'd get in the lab if you dropped a piece of pure copper into a beaker of pure acid. Other metals alloyed with the copper (such as zinc and tin) will be undergoing their own chemical reactions, contributing to the final corrosion product.

    When leather is made, they usually treat the animal hide with acid to soften it. The acid usually used is sulfuric acid, though sometimes formic acid is used instead. Depending on the exact method of processing the leather, some of this acid is retained in the leather and slowly outgasses over time. So, the resultant copper salt from a piece of copper (or copper alloy, such as brass or bronze) from being in prolonged contact with a piece of leather will be copper sulfate - the same salt that forms from PVC damage.

    @Barberian said:
    My understanding is hydrochloric acid (HCl) is a by-product in PVC polymerization and needs to be neutralized during manufacture. I figured the green salts formed on coins might be cupric chloride from residual HCl.

    There's probably a little bit of residual hydrochloric acid in PVC, but most of the acid damage from PVC comes from sulfuric acid, which is added to the PVC alongside the phthalate plasticizer. So the primary cause of the green-ness of PVC goo is copper sulfate. It's green, not blue, because it's dissolved in phthalates, not water.

    The green corrosion that slowly forms on copper objects exposed to the outdoors - think the Statue of Liberty, or the green roofs of neo-gothic buildings like the Canadian parliament - is usually made of a mixture of copper oxide and insoluble copper salts, such as copper carbonate, copper sesquicarbonate and copper hydroxide. The thick dark green patina that ancient copper coins usually feature is made of malachite; the coin is gradually turning back into the copper ore from whence it came.

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  • Namvet69Namvet69 Posts: 8,592 ✭✭✭✭✭
    edited February 1, 2024 4:27PM

    Solder flux also creates Verdigris after a while. Good luck. Peace Roy

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  • jacrispiesjacrispies Posts: 669 ✭✭✭✭✭

    I see that same verdigris on old cameras in leather cases. Nasty stuff but comes off pretty easy.

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  • Insider3Insider3 Posts: 154 ✭✭✭

    Interesting. I know the crud and if it is still soft, acetone removes it; however, if left on the coin it will etch the surface. Ill bet the snaps on the key case are no longer shiny brass. It is found on gold coins too, especially in the recesses of incuse $5 & $2 1/2 Indians.

  • BarberianBarberian Posts: 2,883 ✭✭✭✭✭

    @Married2Coins said:

    @Barberian said:
    My understanding is hydrochloric acid (HCl) is a by-product in PVC polymerization and needs to be neutralized during manufacture. I figured the green salts formed on coins might be cupric chloride from residual HCl.

    Here are some cupric salt crystals and the light corrosion spots often associated with them on a top pop CC coin.

    I am not a chemist; however:

    1. The green crude in the wing looks exactly like the sludge on the copper.
    2. I suspect that the stuff on silver has a different chemical composition than the sludg found on copper.

    Remember that most US silver coins are 10% copper.

    3 rim nicks away from Good
  • RobertScotLoverRobertScotLover Posts: 510 ✭✭✭✭

    Just starred this thread, excellent info on the green crystals commonly found on a great many of our coins. Since they are typically pretty tiny in size the grading companies will ignore them as well as CAC again if tiny

  • silviosisilviosi Posts: 444 ✭✭✭

    On silver and gold, the acetic acid will remove complet.

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  • Married2CoinsMarried2Coins Posts: 136 ✭✭✭

    @RobertScotLover said:
    Just starred this thread, excellent info on the green crystals commonly found on a great many of our coins. Since they are typically pretty tiny in size the grading companies will ignore them as well as CAC again if tiny

    Won't they look liek the green PVC haze? Won't they eventually etch the surface. Are you speaking for CAC and the TPG'ers or just posting something you think is true?

  • RobertScotLoverRobertScotLover Posts: 510 ✭✭✭✭

    In my experience I have sent coins with the tiny green crystal like appearance to all grading companies and they have come back graded 100% of the time. Please understandI am speaking about tiny fly specs of green crystals, and they always got graded and stickered

  • SapyxSapyx Posts: 1,960 ✭✭✭✭✭

    As I mentioned above, a piece of shiny copper metal turning back into a little green rock is chemically inevitable, in the long term; this planet simply doesn't like bright shiny copper. Trying to keep a piece of copper shiny and green-free forever is to fight against the Second Law of Thermodynamics.

    What this means, essentially, is that the TPGs are more lenient towards "little flecks of green" on copper coins the further back in time you go. Green flecks on a Lincoln Memorial cent? No, they'll probably bodybag it. Green flecks on a Fugio cent? They'll probably accept it. Green flecks on an ancient Greek or Roman coin? Absolutely acceptable - they'd probably bodybag an ancient Greek coin that didn't have any green on it, since that would be a sign that it would have been overcleaned.

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