What happened to this coin?

Discussion in 'Ancient Coins' started by SeptimusT, Sep 15, 2019.

  1. SeptimusT

    SeptimusT Well-Known Member

    I'm curious what caused the strange appearance of the silver on the obverse of this coin. I assume it is some type of delimitation, but what could have caused Apollo's hair on the obverse to take the appearance of an exposed brain, while the other is so well preserved? I have to wonder what is beneath the 'flakes,' but as much as I'd like it to be an adhesion from another coin while would reveal a smooth surface underneath, I must assume that it is not attractive. At any rate, I still like the coin, and the reverse is of a very nice style (look at that dog!).

    Obverse: Heroic bust of Apollo left, preparing to hurl thunderbolt, ROMA monogram behind.
    Reverse: Two Lares seated right, each holding a staff, dog between them, head of Vulcan and tongs above.
    Crawford 298, struck at Rome 111/12 BC

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  3. Ryro

    Ryro You'll never be lovelier than you are now... Supporter

    I believe it's horn silvering (?) Just a guess. I have never delt with it myself but seen pics.
    Cool coin btw. I just picked one up about a month or two ago:
  4. dougsmit

    dougsmit Member Supporter

    Your dog is well done.

    My Quinctius below has a similar obverse problem. My guess (nothing more) is that coins of this type were hoarded with other coins and one side was protected by being against other coins while the bad side was exposed to the elements - perhaps in a leather bag that rotted away allowing the soil chemicals to touch the coin???
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  5. Roerbakmix

    Roerbakmix Well-Known Member

    I believe it's horn silver as well. I'm currently in the making of a detailed guide on horn silver, including a section on the recognition and the restoration of it, which I will post on CoinTalk later.

    You can try to chemically remove horn silver using sodium thiosulphate, which is not harmful to the silver, but will dissolve the horn silver (which is silver chloride or bromide - or a mixture of these).

    I'll not delve too much in detail now, but your coin looks like good candidate since it's a) a metallike type deposition, and b) clear breaking lines of these depositions can be seen which smooth and solid, unpitted silver below.

    See for comparison this Menander drachm:
  6. Alegandron

    Alegandron "ΤΩΙ ΚΡΑΤΙΣΤΩΙ..." ΜΕΓΑΣ ΑΛΕΞΑΝΔΡΟΣ, June 323 BCE Supporter

    Amazing what 2000 years can do to any coin.

    This coin’s reverse always reminds me of the final scenes from the film “Close Encounters of the Third Kind”...

    RR Lucius Caesius 112-111 BCE AR Den Apollo Lares Praestites Sear 175 Craw 298-1
  7. Rob Woodside

    Rob Woodside New Member

    Silver Chloride or Bromide or a mixture is not metallic. Horn silver leaves a greenish corrosion and in pokable amounts is is greenish white to light brown and brittle. What has been shown are silver deposited on silver for some unknown reason.
  8. Roerbakmix

    Roerbakmix Well-Known Member

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  9. SeptimusT

    SeptimusT Well-Known Member

    Interesting. So is the consensus that it is either horn silver or silver deposited from another source? I’m quite certain that at least some of it could easily be removed mechanically, but I am concerned about what is underneath. What I can see under the layers does look solid, though.

    Some nice coins on display here too!
    Chuck_A likes this.
  10. PeteB

    PeteB Well-Known Member

    Where can sodium thiosulphate be purchased?
    And how is it used?
    Looking forward to your article on this.
    TIF likes this.
  11. Roerbakmix

    Roerbakmix Well-Known Member

    I'm currently studying several archeological and numismatical articles on the restoration of ancient silver. There seems to be no consensus article on horn silver, which I aim to write.

    Sodium thiosulphate can be bought at some drug stores. It's relatively cheap: I bought 200 gram for €4,00. On the average coin with horn silver, I use approx. 2-3 gram.

    I will post the draft version of my article probably this month.

    A general advice to @SeptimusT: I would not clean the coin mechanically, but start chemically. Please note that every kind of cleaning will alter the patina of the coin: underneath the horn silver, there will be no patina. Sodium thiosulphate however reacts with the AgCl creating Na3[Ag(S2O3)2] and NaCl. The Na3[Ag(S2O3)2] has a nice, dark appearance which is common to 'cabinet toning' (which makes me wonder about artificial patina in general).

    In my opinion, although I prefer to see the coin in hand, you can safely start with sodium thiosulphate.
  12. Rob Woodside

    Rob Woodside New Member

    Thanks for the Wikipedia ref. No where does it say Chlorargyrite is metallic. It says:
    "Typically massive to columnar in occurrence it also has been found as colorless to variably yellow cubic crystals. The color changes to brown or purple on exposure to light."

    According to Mindat ( https://www.mindat.org/min-1014.html ) The lustre of Chlorargyrite is "Adamantine, Resinous, Waxy" and not Metallic.

    So the metallic blob is Silver or some metal and not Horn Silver. I think you'd have to have the coin in hand and perhaps other examples to see if the hair has corroded that way or is some added metal.
    Last edited: Oct 12, 2019
  13. Plumbata

    Plumbata Well-Known Member

    I don't know the composition of the material, on coins I've worked on it seems like re-deposited brittle microcrystalline metallic silver, though I've encountered nodules or crusts of waxy purple(ish) chloride on some coins like that as well.

    I'd like to submit before-pictures of a 21.5mm 8.3g Corinthian stater I picked up relatively recently for 110 euros shipped, not a steal given the first-glance appearance but I was able to remove practically everything mechanically so it's quite attractive now and definitely worth the price, I'll have to take pics to share with you the lovely results. Seller pics:

    cor1.jpg cor2.jpg
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  14. dougsmit

    dougsmit Member Supporter

    When we met I could have given you a bunch of it but no more. Sodium thiosulphate was common photo fixer. It dissolved unexposed and undeveloped silver halides (chloride, bromide etc.) leaving a more permanent image we called a photograph. That material would dissolve horn silver. Chloride would darken when exposed to light. Early photos faded or actually darkened to black until it was discovered that thiosulphate would dissolve unexposed halides and leave the darkened ones.

    Later, photo technology evolved and added a substance that hardened the film that reduced the effectiveness on coins. Then they invented what was called 'Rapid fixer' that was better for photography but did nothing for coins. Toward the end of my time in the Army, it was getting hard to find the old style fixer. In 2000, I bought a digital camera and never again owned any fixer. I'm sure you can buy the stuff in reagent purity today but back then the stuff was cheap as dirt in good enough for photo and coin quality. Well used photo fixer could be used to silver plate copper pennies. This was long before people decided that they should recover the silver from used photo chemicals. Another useful chemical for coin cleaning as I recall was called 'Farmer's Reducer'. It was used to lighten over exposed negatives to make them usable. It was a set of two baths Potassium fericyanide(?) and thiosulphate. I have forgotten when I used both and when I used just the fixer.

    All I remember about the practical use is that removing an evil (horn silver or other) was no guarantee that what was under the stuff was any better looking than it was to start.
  15. PeteB

    PeteB Well-Known Member

    Thanks, Doug.
  16. SeptimusT

    SeptimusT Well-Known Member

    How timely that this thread was brought back to the top! I was planning to post an update soon. I must confess that I did not follow @Roerbakmix's excellent advice to a T (sorry), since I did begin with some careful mechanical cleaning. The deposits on Apollo's hair came off with a bamboo skewer almost no effort applied, revealing the surfaces you'll see below underneath.

    After a brief soak in distilled water (there was a powdery residue beneath the adhesions), a level of detail I consider equal to the rest of the obverse was found preserved on the hair underneath, so I consider it a success. The question now becomes whether I should leave well enough alone, or whether I should use sodium thiosulphate to try and remove some of the other additional deposits which leave the obverse looking rough.

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  17. Roerbakmix

    Roerbakmix Well-Known Member

    No offence taken ;) I still believe this coin would greatly benefit from a sodium thiosulphate immersion: I would definitely do it. Mechanical cleaning is, in my opinion perfectly okay if done properly (i.e. correct use of force with the correct tools). Though a bamboo skewer will likely not harm the coin, I noticed some scratches on the coin that were not there before. On this coin of a likely high silver concentration, I would personally refrain from doing so and stick to the chemical arsenal.

    However, what @dougsmit says is correct:
    You won't know what's beneath the corrosion until you remove it. However, as I pointed out in my first post, the breaking lines in the horn silver are a good indication of a solid, smooth surface below.
    E.g., the deposit depicted here, with clear breaking lines:
    fig 5c.JPG
    was easy to remove, while the rough deposits without clear breaking lines (below), were not.
    fig 6c.JPG

    In conclusion: you already have a coin with a rough appearance, with a decent chance of a smooth surface below, and a relatively smaller chance of a rough surface below (i.e. your starting point). The 'pure' silver, nor the silver sulphate patina will be altered by the sodium thiosulphate - it reacts with the chlorides or bromides only. I would still do it. It's fun :)
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