what causes parallel ridges on a coins surface?

Discussion in 'US Coins Forum' started by WingedLiberty, May 11, 2014.

Page 2 of 2
  1. coppertoning

    coppertoning Well-Known Member

    WL ;) knew who I was referring to
     
    coppertoning, May 11, 2014
    #21 + Quote Reply
  2. Avatar

    Guest User Guest



    to hide this ad.
  3. GDJMSP

    GDJMSP Numismatist Moderator

    That's debatable. It is generally agreed that heat is what causes the blisters, but the heat from annealing is much greater than the heat generated from the strike, and thought to be the culprit. So they would be there before the strike.

    Also, most blisters are round or roundish in shape and haphazard, not in a parallel series of narrow lines. I readily agree that round blisters typically do not break, nor is it uncommon to find them on the devices, and in the fields.

    As I said earlier, whatever it is that caused the lines, I definitely suspect they were on the zinc planchet before it was ever plated. If you look closely, the lines left of the bust line up with those on the right. In other words, they are one continuous line. And because the zinc is so soft, that would explain why the lines are not visible on the devices - they were obliterated by the strike.

    That is the only thing that makes sense to me. Even so, that is conjecture as I have never seen a coin like this.
     
    GDJMSP, May 12, 2014
    #22 + Quote Reply
  4. LindeDad

    LindeDad His Walker.

    Could also be a problem of the two coats of copper adhering to each other as proofs are doubled plated.
     
    LindeDad, May 12, 2014
    #23 + Quote Reply
  5. jallengomez

    jallengomez Cessna 152 Jockey

    I can only speak for Lincoln Cents such as the one posted because that's my specialty, but I can say that with copper plated Cents, linear plating disturbances caused by gas trapped between the core and the plating are not uncommon at all.

    Regarding the cause of the blisters, when it comes to Lincoln Cents, everything points to them being caused by the strike, because with off-center cents where blisters are present, the unstruck part of the planchet does not show the blisters. One might exist, but I've yet to see an unstruck planchet or unstruck portion of a planchet that exhibits plating problems. It it's debatable, then these would certainly have to exist.
     
    jallengomez, May 12, 2014
    #24 + Quote Reply
  6. rlm's cents

    rlm's cents Numismatist

    These are anything but rare. A quick check found these. They are all business strikes, but I also have several proofs. And these lines run through the devises.

    BTW, I suspect Doug is on the right track saying they originate from the zinc core, but I can guess no more.

    1984- O.JPG 1984-D O.JPG 1985- O.JPG 1986- O.JPG
     
    rlm's cents, May 12, 2014
    #25 + Quote Reply
  7. GDJMSP

    GDJMSP Numismatist Moderator

    Those I've seen, but in all of them the lines are on the devices too. It's none being on the devices in OP's post that makes me wonder. But I wouldn't say those are attributable to blisters either, but something wrong with the zinc planchet before it was plated.
     
    GDJMSP, May 12, 2014
    #26 + Quote Reply
  8. rlm's cents

    rlm's cents Numismatist

    My proofs are going to be a lot harder to catch, but my 85-S, 87-S, 88-S, 89-S and 90-S all have the lines and all end at the devises. So the devise portion of this must have something to do with the minting process.
     
    rlm's cents, May 12, 2014
    #27 + Quote Reply
  9. GDJMSP

    GDJMSP Numismatist Moderator

    Could be Dick, I suppose it's entirely possible that when the lines are not as bad as they are on some coins that the strike-up could be obliterating them, flattening them out in other words.
     
    GDJMSP, May 12, 2014
    #28 + Quote Reply
  10. rlm's cents

    rlm's cents Numismatist

    Lousy pictures, but I think it shows the lines. And this one is bad - line-wise.

    1988-S O.JPG 1988-S Oa.JPG
     
    rlm's cents, May 12, 2014
    #29 + Quote Reply
  11. jallengomez

    jallengomez Cessna 152 Jockey

    I imagine it has something to do with the minting process of proofs. For some reason, the lines tend to be less pronounced and less likely to extend to the devices on proof issues.
     
    jallengomez, May 12, 2014
    #30 + Quote Reply
  12. GDJMSP

    GDJMSP Numismatist Moderator

    Well, I was thinking that it might be because Proofs are struck with higher pressures than business strikes. But the part of the planchet the undergoes all the pressure is the fields. So you would think if pressure was it that the ridges in the field areas would get flattened out. But they obviously don't.

    Proofs are also struck at least twice and sometimes more than twice, so maybe that's what it takes to obliterate the ridges in the device areas ??? I dunno, it really doesn't make sense to me as to why it happens, but it obviously happens.
     
    GDJMSP, May 13, 2014
    #31 + Quote Reply
  13. WingedLiberty

    WingedLiberty Well-Known Member

    Interesting discussion ... thanks for all the ideas.
     
    WingedLiberty, May 13, 2014
    #32 + Quote Reply
  14. robec

    robec Junior Member

    I think these are on proofs, but because of the cameo finish they are difficult to see.

    [​IMG]

    [​IMG]
     
    robec, May 13, 2014
    #33 + Quote Reply
    jallengomez likes this.
  15. GDJMSP

    GDJMSP Numismatist Moderator

    They're sure on the devices on those, no question. And it makes it even harder to figure out o_O
     
    GDJMSP, May 13, 2014
    #34 + Quote Reply
  16. bdunnse

    bdunnse Who dat?

    Is it actually ridges or is it just coloring/luster/material striations? No clue in general, just tossing out a random thought.
     
    bdunnse, May 13, 2014
    #35 + Quote Reply
Page 2 of 2
Draft saved Draft deleted

Share This Page