Corrosion on some of my silver coins? what to do?

Discussion in 'Ancient Coins' started by iameatingjam, Sep 10, 2022.

  1. iameatingjam

    iameatingjam Well-Known Member

    I haven't looked at my coins in a good 6 months, when I pulled them out the other day a couple had ... something... on them. Looked kind of like bronze disease but also kind of different. This is what it looks like, its the bluish stuff:


    This denarius had some on it too, I forgot to take a picture but even from this you can see that it looks like its been harshly cleaned in some areas, and thats where it came in, so maybe it had it before?


    Anyway some acetone took it off really easy. Now I just want to try and prevent it from coming back. I've already put some silicia packs in with them... Would verdi-care be right for this? Or something else? Also, what is it? Bronze disease? Or from pvc maybe? It didn't seem as crumbly as the bronze disease that I've seen before...

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  3. Cherd

    Cherd Junior Member Supporter

    I'm no expert on the subject, but isn't verdigris specific to copper or copper containing alloys? I know that Roman silver wasn't pure, and I'm pretty sure that they mixed some % of copper into them, but my intuition is that coins of the republic or even up to Pius would not contain enough copper to have verdigris sprouting up like that. Then again, I could be completely wrong.

    If it is verdigris, then you should be able to detect some mass loss under the spots where it was located (etched looking and/or pitted surface). If the surfaces under green substance looks unaltered compared to the rest of the surfaces, then I'd say that it was not verdigris. But, again again, I could be wrong.
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  4. iameatingjam

    iameatingjam Well-Known Member

    Yeah thats what I thought too but I found a thread on here that said silver can get it too...? The denarius is Caracalla by the way, so there's definitely some copper in there. Enough ? Don't know.

    To your second point... yes thanks for reminding me, I was going to bring that up. It didn't seem like whatever it was, was eating away at the metal in the same way bronze disease does. The coins looked pretty much the same after I cleaned them as before this happened... but thought maybe thats because I caught it early?

    Do you know what else it could be? I did have the stater in a pvc slip for a while ( 2 months maybe) when I first started collecting and didn't know any better. But that was a long time before this happened. I don't think the denarius ever was while in my possession.
    Mr.MonkeySwag96 likes this.
  5. johnmilton

    johnmilton Well-Known Member

    Silver can corrode if it has not been stored properly, like in the ground. Usually the corrosion is black or dark brown and porous. The green stuff has to be from the copper that’s in the piece.
  6. Collecting Nut

    Collecting Nut Borderline Hoarder

    Nice looking coin. Hope you get to the bottom of what’s going on.
    iameatingjam likes this.
  7. sand

    sand Well-Known Member

    @iameatingjam I wonder if it's PVC. How do you store your coins? Do you store your coins in coin flips? Are the coin flips PVC free?
    svessien and Insider like this.
  8. Cherd

    Cherd Junior Member Supporter

    There's a reason that I don't do my own coin attributions :)

    The bust didn't look like any Pius that I'd ever seen, but the name is plainly spelled out on the coin. Guess that's not very informative when they all perpetually recycled the same names!

    I did a quick search on PVC damaged silver coins, and the photos suggest to me that this is a good candidate for your issues. Maybe some residue was left on the coin? Or the problematic gases managed to penetrate some micro-porosity? The discoloration seems to be restricted to only the high points on the coin, so that further supports this theory IMO.

    Seems to me that, if this type of thing was on the surface, then the acetone would have removed it. Hopefully that did the trick ;)
    iameatingjam and sand like this.
  9. johnmilton

    johnmilton Well-Known Member

    Yes, it could be, but that is usually green. If you can push it off, do so. I've also done with Goo-Gone and it didn't hurt the medalet a bit.

    Here's two examples. The original buyer bought these Lincoln pieces in an auction and left them in the original flip for years. The PVC flips did their thing, but the medales

    came out okay.

    AL 1864-8 O.jpg AL 1864-8 R.jpg

    AL 1860-12 O a.jpg AL 1860-12 R a.jpg
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  10. RichardT

    RichardT Well-Known Member

    If the stuff was blue, like you said, then it was likely to be natural toning (aka tarnishing) of silver. Silver reacts with sulfur in the air, turning a variety of shades (blue, orange, brown) before turning black eventually.

    Sulfur is everywhere, partly due to combustion engines. Trying to prevent the blue stuff from appearing again would be very difficult, unless the coin is kept in an air-free environment somehow. Not practical I would say.

    Speaking generally, this toning tends to be desired on ancient coins. It proves that the coin has been out of the ground for some time.

    True verdigris is rock hard and can't be removed by acetone.
  11. iameatingjam

    iameatingjam Well-Known Member

    I have them in proper fabric trays now, but when I first started collecting I had them in pvc slips for a while ( bad I know ) but only the stater was in there. The infection definitely looked more advanced on the denarius, possibly even something different I don't know... I should have taken a picture of that.

    I hadn't considered that it was just a patina. It didn't strike me as that, but I could be wrong.
    sand likes this.
  12. robinjojo

    robinjojo Well-Known Member

    I would definitely get rid of any flips that might have PVC, and move the coins to safety flips. The old PVC flips are quite soft, while safety flips are rigid. You might consider buying a box of safety flips that you can use as needed.
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