Crystallized silver

Discussion in 'Ancient Coins' started by hotwheelsearl, Mar 5, 2021.

  1. hotwheelsearl

    hotwheelsearl Well-Known Member

    Thought I’d share a mega close up of crystallize silver on a broken RR denarius.

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  3. YoloBagels

    YoloBagels Well-Known Member

    I had a denarius crystalized just like this one. Broke after I took it out of a 2x2 Mylar. Sold it to a friend for $3.
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  4. JayAg47

    JayAg47 Well-Known Member

    Is crystallized silver meaning the silver reacted with the air forming layers of silver salt, or just metallic silver hardening over time, thus shrinking and creating small cracks resembling a crystal structure?
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  5. hotwheelsearl

    hotwheelsearl Well-Known Member

    Honestly, I'm not sure. I just know that some silver coins break easily because the silver "crystallizes." I feel like @desertgem may be the chem guy in the house.

    The crystalized part looks unlike regular silver, it has a crystalline structure although why that is is beyond me.

    The coin in question is L Memmius Galeria:
    L Memmius Galeria (2020_11_18 03_38_31 UTC).JPG
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  6. David Betts

    David Betts Elle Mae Clampett cruising with Dad

    Back when I was in construction we'd take a bunch of silver coins and purge with Liquid Oxygen -325* degrees and put in bag and smash on steel beams I'll look for the remnants! awesome
  7. Kentucky

    Kentucky Supporter! Supporter

    Most materials can be crystalline or amorphous. Metals tend to form crystals. The material is 100% (or whatever) silver, it's just in its crystalline form rather than its amorphous form.
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  8. otlichnik

    otlichnik Well-Known Member

    It's a process called "embrittlement" whereby there is a very slow reaction between different elements in the metal matrix that were imperfectly mixed (or in some cases that were insoluble vis-a-vis each other). In silver coins it usually forms along the grain boundaries between silver and lead and/or silver and copper. The boundaries between these grains in effect form microscopic cracks. The exact nature of the alloy - its contents, the degree to which it was mixed, the way it cooled - all contribute, as does the conditions of its burial. So presumably, while some issues may be more susceptible, the real factors are unique to each individual coin.

  9. Marsyas Mike

    Marsyas Mike Well-Known Member

    Here's a budget hemidrachm from Kallatis that appears to have crystalized internally - a big chip off the edge shows the granular-looking interior. Although the surface looks fairly normal and smooth, there is also a big, shallow crack that threatens to make the face fall off. Safe to say this one is "fragile"!

    Sorry for the worse-than-usual photo - got a bit of sun glare on this one:

    Kallitas - Hemidrachm Nov 2020a (0).jpg

    Kallitas - Hemidrachm Nov 2020a (1).JPG

    Thrace, Kallatis Hemidrachm
    (c. 300-101 B.C.)

    Head of Herakles right wearing lion skin headdress /ΚΑΛΛΑ, club and ear of barley below, bow in bow case (gorytos) above.
    AMNG I-I, 201.
    (2.13 grams / 14 mm)

    Attribution Note:
    These often have a letter in the field (Φ, A, O, Σ etc.), which might be off flan on this specimen.

    Attribution from Numista, with no letters noted.
  10. robinjojo

    robinjojo Supporter! Supporter

    Nice photo!

    The silver looks as if it totally altered to a silver oxide (Ag2O).
  11. Kentucky

    Kentucky Supporter! Supporter

    except that Ag2O is black.
  12. otlichnik

    otlichnik Well-Known Member

    Yes Ag2O is a surface oxidization product, not the cause of embrittlement or crystallization.

  13. Kentucky

    Kentucky Supporter! Supporter

    Side story, many organic chemicals are hard to make crystallize and there was a well known chemist who would scratch his beard over a solution to make the dissolved organic start to crystallize... :)
  14. desertgem

    desertgem MODERATOR Senior Errer Collecktor Moderator

  15. robinjojo

    robinjojo Supporter! Supporter

    That's true, the embrittlement is a combination of oxidation and the leaching of copper alloy, leaving a dark, brittle crystalline surface that over time becomes increasingly thicker, until the entire coin is altered.

    Now I have a tetradrachm that had very heavy oxidation that did penetrate fairly deeply, much to my dismay when I attempted to remove some of, only to see a lot of the detail melt away.
  16. Marsyas Mike

    Marsyas Mike Well-Known Member

    While taking do-over photos of my Severan silver, I came across this denarius of Severus Alexander. It has an edge chip revealing what looks to be internal crystallization, although the surfaces are pretty nice.

    Severus Alex. - Den. Salus RIC 178 AZ c. 1999 (0).jpg

    Severus Alex. - Den. Salus RIC 178 AZ c. 1999 (0det).JPG
    Severus Alexander Denarius
    (c. 222 A.D.)
    Rome Mint

    IMP C M AVR SEV ALEXAND AVG, laureate, draped bust right / SALVS PVBLICA, Salus seated left, with patera, feeding serpent rising from altar.
    RIC 178; Sear 7952.
    (2.38 grams / 19 mm)
  17. Mr.Q

    Mr.Q Well-Known Member

    I learn something new everyday on CT, thanks everyone.
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  18. fullhart

    fullhart Junior Member

    Can the crystal be changed back into solid silver? By heat, or chemical reaction? Would the coin be damaged if an attempt was made to change from crystal to solid?
  19. desertgem

    desertgem MODERATOR Senior Errer Collecktor Moderator

    The silver might revert, but the method would be extreme enough to ruin the coin. The crystallization might be the major part holding the coin together. I would certainly leave it as is. IMO, Jim
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  20. Kentucky

    Kentucky Supporter! Supporter

    You could think of it as honey in a jar that sometimes crystallizes. The only way to liquify it is to heat it up. Don't try that with coins.
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  21. Rob Woodside

    Rob Woodside Member

    1) I don't think silvers oxidizes to Ag2O but rather to Ag2S which is black and irridescent in thin films

    2) you are looking at age hardening that can embrittle the coin severely. If the alloy is severely debased it may be unstable and the impurities diffuse to the grain boundaries embrttling the coin. On the fracture you see a typical brittle fracture that looks like the pictures. Basically the alloy is recrystallizing to stable compounds.

    With the advent of electron microscopes in the '60s it became possible to identify metals in a micron sized patch. When they did this to lab crystallized Pt alloys they couldn't find the same compounds occuring in ancient Pt nuggets. This was explained by saying the lab grown stuff wasn't in equlibrium as it hadn't the millions of years for the alloys to diffuse to their most stable state. I'm amused that classical coins have been around long enough to do so.
    Last edited: Mar 7, 2021
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