Looks like burnt paint for patina what do you think?

Discussion in 'Ancient Coins' started by bcuda, Aug 23, 2020.

  1. fomovore

    fomovore Supporter! Supporter

    Sure, you can remove the oxidation which will result in a pitted surface. If the surface isn't pitted, it wasn't oxidation hence not horn silver.
     
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  3. RichardT

    RichardT Well-Known Member

    I may be wrong, but to me it just looks like a denarius which has tarnished/toned to black. It is quite common for silver coins to tarnish unevenly.
     
  4. bcuda

    bcuda Supporter! Supporter


    No way in hell is it a tarnished coin!
     
  5. RichardT

    RichardT Well-Known Member

    I certainly wasn't expecting such a strong reaction, or language.

    What makes you sure it isn't it a tarnished coin?

    I don't know what "burnt paint patina" is, but I'm pretty sure this coin hasn't been in a fire if that's what you're saying.
     
  6. dltsrq

    dltsrq Grumpy Old Man

    Horn silver (AgCl) comes in a variety of textures and colors. Sometimes it looks a bit like tar, as on this coin.
     
    Last edited: Aug 23, 2020
  7. fomovore

    fomovore Supporter! Supporter

  8. Roerbakmix

    Roerbakmix Well-Known Member

    I wrote a thing or two about horn silver and restoration of coins with horn silver.

    The patina of this coin is very characteristic of horn silver. Please find my elaboration on horn silver here:
    https://www.cointalk.com/threads/wh...-admission-49-532-49-533.362851/#post-4607392

    I would characterize this type of horn silver as type I:
    upload_2020-8-24_9-15-50.png

    By the way: I would not treat this coin. I expect severe pitting underneath the horn silver.
     
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  9. EWC3

    EWC3 (mood: stubborn)

    Correct
     
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  10. RichardT

    RichardT Well-Known Member

  11. Roerbakmix

    Roerbakmix Well-Known Member

    Basically, horn silver can form on any silver coin, if exposed to high concentrations of Chloride or Bromium (AgCl or AgBr) for a sufficient period of time. I've seen it on medieval coins (this is the same type of HS as the coin of OP):
    [11128] Diederik van der Ahr - Utrecht, the Netherlands (AR penny, 1197-1212) [uncleaned].jpg [11128] Diederik van der Ahr - Utrecht, the Netherlands (AR penny, 1197-1212).jpg

    ... Roman (this is the metallic type):
    [1151] Hadrianus - Rome, Italy (AR denarius, 134-138 AD) (uncleaned).jpg [1151] Hadrianus - Rome, Italy (AR denarius, 134-138 AD) (cleaned).jpg

    [1155] Hadrianus - Caesarea, Cappadocia (AR didrachm, 128-138 AD) [uncleaned].png
    [1155] Hadrianus - Caesarea, Cappadocia (AR didrachm, 128-138 AD).jpg

    Greek (still have to clean this one):
    WhatsApp Image 2020-08-17 at 08.51.00.jpeg

    ... Carolingian (didn't clean it, as it was too unstable):
    [11127] Charles II le Chauve - Melle, France (AR Denier, 843-877).jpeg
    ... Anglo-Saxon (again the metallic type):
    upload_2020-8-24_11-11-30.png

    etc.

    Restoration of horn silver can be lucrative, if you know what you're doing. Uncleaned coins usually sell for way lower prices.
     
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  12. justus

    justus New Member

    I think it is quite possible that this could be a former antique patina burned in a fire. Some decades ago I was able to acquire a cast or bronze denarius (Limes denarius), which could be recovered from the fire debris of a ruin years after the firestorm of the allied bombing raids on Hamburg in 1944/45. The similarity seems obvious to me.
     
  13. RichardT

    RichardT Well-Known Member

    Thanks Roerbakmix for sharing those images. I stand corrected.
     
  14. Roerbakmix

    Roerbakmix Well-Known Member

    There doesn't really have to be a difference between 'burnt patina' and horn silver: the chemical reaction leading to the formation of AgCl or AgBr could have been formed during a fire, or during centuries in favorable conditions: the results are the same (horn silver)
     
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  15. justus

    justus New Member

    Thanks for the information. This was not known to me until now!
     
  16. Co1ns

    Co1ns Active Member

    Thanks for sharing Roer, great stuff. Off and read all your other posts on this topic after that. I knew the metallic deposits were horn silver, but I always thought that black waxy stuff was just dirt/clay/muck.

    Question re: sodium thiosulphate, does this have any effect on the stubborn green and red gunk found on bronzes?
     
  17. Roerbakmix

    Roerbakmix Well-Known Member

    @Co1ns, thanks! Appreciate the compliment.

    No, I would not think so. These deposits are something different than AgCl and/or AgBr, so it's not 'one treatment fits all'.
    I must say, I find bronze very hard to treat well and usually refrain from doing so. The only caveat of silver coin restoration is the often very soft patina (and underlying metal) in combination with the usually very hard deposits.
     
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  18. EWC3

    EWC3 (mood: stubborn)

    For cleaning purposes I would say there are two kinds of coins with horn silver deposits

    A) Ones where the silver derives from the host coin itself - which means there will be pitting underneath proportional to the encrustation on top.

    B) Ones where a different coin in the ground - close by - corroded and the deposit is composed of material transferred onto the host coin

    Obviously cleaning type B is a good idea, type A - less so.

    So the key question is not how to clean - but whether to clean.

    Obviously too - if horn silver is "chipping off" - it points towards at least some of the deposit being transferred.....

    R
     
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  19. Roerbakmix

    Roerbakmix Well-Known Member

    @EWC3 classifies it in the same way as I see it. If horn silver is deposited on the coin (e.g. part of a coin hoard where the outer coins degrade), the results are usually fine. In another thread, I just posted the cleaning process of a coin which I suspect was part of a hoard:

    before:
    upload_2020-8-26_9-49-46.png
    after:
    upload_2020-8-26_9-49-49.png
    This one would fit in the first category: the horn silver is upon the coin, and the surface below is smooth.

    This one however is different:
    before:
    upload_2020-8-26_9-50-50.png
    after:
    upload_2020-8-26_9-51-0.png

    Note that on some places (e.g. on the obverse at 7 o clock; on the reverse ate 9 - 11 o'clock), there is pitting, while on other places (e.g. on obverse at 3-5 'o clock; reverse in the field and legend) the metal is smooth. I expect degradation of the places with pitting, and deposition of the AgCl on the other parts of the coin.

    Same with this one:
    before:
    upload_2020-8-26_9-53-4.png
    after:
    upload_2020-8-26_9-53-9.png
    a pitted obverse, with a very sharp reverse.
     

    Attached Files:

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  20. EWC3

    EWC3 (mood: stubborn)

    A rare event and cause for celebration :)

    Aside from cleaning (very many) such coins I have been paid by trade to clean their own (4 figure value) coins but also paid to merely give an opinion on whether to clean. But I find this track record counts for little in our new web based form of democracy

    R
     
  21. RichardT

    RichardT Well-Known Member

    I do apologise if I have offended anyone with my doubts and questions. Sorry.
     
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