The Dreaded Speck O' Green

Discussion in 'Ancient Coins' started by Clavdivs, Jan 26, 2020.

  1. Clavdivs

    Clavdivs Well-Known Member

    While handling a few coins I have neglected for the last few months I found this on my coin of Agrippa:

    Agrippa_Merge.JPG
    Better image:
    Agrippa Green.JPG
    This is only the second time I have found what I believe may be "bronze disease" - oddly enough both instances have been found on coins of Agrippa!

    My first coin has/had a more serious "infection" (that came with the coin.. and had taken hold very seriously prior to me owning the coin!) I thought I had that cured but it returned with a vengeance and may or may not destroy the coin. ..TBD.

    This instance was found quite early so I feel should have a better chance of success.

    Here is what I have done tonight:

    1) separated the coin from my collection
    2) put the coin in a glass of Distilled water

    I do own Verdicare - although I had not applied it to this particular coin ..

    So is my best process to change the distilled water daily and see if I can brush/scrape off the green? Continue this for many weeks/months until I see things clear up - then add Verdicare?

    Thanks for your advice in advance....
     
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  3. ominus1

    ominus1 Well-Known Member

    ..my advice...quickly and often...i'm glad you posted this..imma gonna go thru my bunch too now...:)
     
    Last edited: Jan 26, 2020
  4. thejewk

    thejewk Well-Known Member

    I think the first course of action is manual removal of all of the green with a toothpick, and then whatever soaking treatment you decide on. That seems to be the accepted method I've seen, but I have no experience myself yet.

    Good luck!
     
    TIF likes this.
  5. Nicholas Molinari

    Nicholas Molinari Well-Known Member

    You need to neutralize the reaction with sodium sesquicarbonate.
     
  6. gsimonel

    gsimonel Supporter! Supporter

    Yes, if you haven't already removed to green powder manually, do so immediately. Then continue soaking the coin in fresh batches of distilled water, changing it every day or two for the next few weeks. I usually go around 6 weeks.

    BTW, if the green does not brush off easily, it's not bronze disease.

    I don't think you need Verdicare, but it shouldn't hurt the coin as long as you let it dry thoroughly before you apply it. However, I think you should let the coin sit out in the open some place where you will see it often for about 3-6 months to make sure that the bronze disease does not return before you apply anything to the surface. You don't want to seal the BD inside the coin. Every now and then I've had BD return--probably because I was too impatient in treating it and didn't get it all--and had to do a second round of soaks. So far--knock on wood--I've never had BD return a third time.

    I've never used sodium sesquicarbonate, but it's a relatively safe chemical to handle, and it may speed up the process. I have heard other people recommend it, I've just never needed it.

    Good luck treating your coin.
     
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  7. Nicholas Molinari

    Nicholas Molinari Well-Known Member

    It’ll turn the spot red, which is a stable state.
     
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  8. JulesUK

    JulesUK Active Member

    I’m dreading my first Bronze Disease. Mainly in case i miss it.
    How often should one check for BD?
    How quickly can it spread from coin-to-coin?
     
  9. Bing

    Bing Illegitimi non carborundum Supporter

    Many years ago I purchased the coin shown below. It was hard to miss the disease when it was received. I treated it immediately and for several months and I examine it periodically to make sure it does not make a reappearance. So far, so good. However, as you can see, the BD had already done much damage. Even though the image shows some green, the coin no longer does (I'm just too lazy to take another image).
    Agrippa 2.jpg
    AGRIPPA
    AE As
    OBVERSE: M AGRIPPA L F COSIII - Head left, wearing rostral crown
    REVERSE: No legend - Neptune standing left, holding dolphin and trident; S C across fields
    Rome 37-41 AD
    11.0g, 28mm
    RIC58, BMC 161, BN77, C3
     
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  10. gsimonel

    gsimonel Supporter! Supporter

    You should look over your bronze coins at least once every 6 months or so. If BD is going to appear, it is most likely to show up within 6 months of a coin being cleaned. If it hasn't shown up by then, chances are your coin won't get it.

    I've not heard of it spreading from one coin to another.
     
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  11. otlichnik

    otlichnik Member

    BD is a pain. Here is my reaction to a possible case of BD:

    1) Is it BD?? Lots of people mistake different hard corrosion/reaction products - like malachite - for BD. BD is soft and powdery not hard and crystalline. In the case of the coin here it certainly does appear to be BD.

    2) Remove the current BD. Most should be removable with soft tools - toothpick, bamboo skewer, hard (cut-down) toothbrush or other nylon brush. Try to get all of it off. When you think it is all gone keep working it with a softer brush, q-tip, micro-fibre cloth etc. to make sure. Sometimes it is necessary to use stronger tools - steel pins, soft brass brush, etc.

    3) When BD is removed soak in DW (distilled water) for 24 hours. Then dry. Then bake dry in oven (not microwave!!!) at low temperature (say 200 F for 15-20 minutes) to remove all moisture.

    4) Leave the coin for weeks and monitor it. Do not coat the coin with anything at this stage! This will just seal in whatever is there - including remaining BD if it is not all gone. And the BD can still be there invisibly - that is why this waiting stage.

    5) If the BD returns repeat. Or repeat + add sodium sesquicarbonate boil. Or, if really stubborn, repeat + treat with benzotriazole (a potentially carcinogenic substance so research well and use properly!!!).

    Warning: Other than the returning BD, there are two bad scenarios.

    The first is the extensive BD under a solid-looking crust. I do have some concerns that this might apply to the coin shown in this thread. In these cases, the BD is not confined to a "pit" but is more like the lake under a frozen surface. The surface will often be flakey and break during cleaning. I have no good solution for this nightmare scenario though I would avoid any tools and stick to soaks.

    The second is the powdery surface - where the entire surface suffers from a BD-like decay and any treatment - sometimes even a DW soak - removes all detail leaving a slug. This is usually found on late Roman bronzes from areas where lots of fertilizer was used (Britain, France, etc.) or highly acidic soil (some "Holy-land" coins). In my experience, all that can be done with these coins is to identify them before treatment and either leave them as is, or sometimes rub them gently between thumb and finger - I know that sounds odd but this can sometimes slightly stabilize the surface a bit, though any subsequent treatment, brushing or soak will still destroy the surface.

    SC
     
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  12. Clavdivs

    Clavdivs Well-Known Member

    Ok - excellent advice here. I have used a toothpick and removed what I could - this did come off in a flaky manner quite easily. The coin is now soaking in DW.. I will leave it for 24 hours and take it out and let it dry. Then see if any more green stuff remains .. hopefully I got it all. If not I will remove.
    I will then return to fresh DW and keep changing that daily for the next 6 weeks.
    Will post my progress.

    Thanks to all who responded with advice.
     
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