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double rim effects

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  • Mike Diamond
    To expedite matters, I have copied post #2007, taking the opportunity to add some other entries.
    Message 1 of 4 , May 5, 2003
      To expedite matters, I have copied post #2007, taking the opportunity
      to add some other entries.

      <<It's very common to come across error coins, and even ordinary
      coins,
      that appear to have a "double rim". A true double rim is, of course,
      impossible, as there is only a single rim gutter in the die face.
      There is more than one cause for this effect:

      1. Finning. When striking pressure is a bit too high, or one of the
      dies is slightly tilted, metal is forced up into the gap between the
      die neck and the working face of the collar. This is called a "fin"
      or a "finned rim". Anyway, the fin lies outside the true rim and, if
      it is low, appears to constitute an extra rim.

      2. A false rim is sometimes seen in misaligned dies and minor,
      uncentered broadstrikes. Coin metal rises into the rim gutter,
      marking the location of the true rim, but a false rim is created
      lateral to that as metal is pushed against the collar (in the case of
      an in-collar misalignment), or it simply bulges out lateral to the
      true rim line (in the case of an uncentered broadstrike).

      3. In the case of a misalignment, or a coin struck in an oversized
      collar (rare), you sometimes see a pressure ridge internal to what
      looks like the true rim. Neither is a rim in the truest sense. Both
      are pressure ridges created by the die being too far from the working
      face of the collar. The inside pressure ridge marks the location of
      the rim gutter (although it hasn't filled it), and the outside
      pressure ridge marks where metal has piled up against the working
      face of the collar.

      4. Die fatigue. Sometimes in late die states, the working face of
      the die deforms in such a way as to create a false rim internal to
      the true rim. This is best seen in copper-plated zinc cents.

      5. Collar clash. When a die collides with the top of the collar, this
      is known as "collar clash". In denominations with smooth edges, it
      can show up as a "double rim". In denominations with reeded edges,
      the top of the rim will show a characteristic serrated pattern.

      6. Partial collar. If the collar is only partly deployed, then metal
      can expand over the top of the collar, creating a false rim lateral
      to the true rim created by coin metal filling the rim gutter of the
      hammer die.


      --- In errorcoininformationexchange@yahoogroups.com, "Mike Diamond"
      <mdia1@a...> wrote:

      > There are many causes for incomplete "double rims" on US coins, but
      > these are always concentrated on one side of the coin, never
      forming
      > a complete ring. Search the archives under keyword "double rim"
      for
      > more information.
    • Mike Diamond
      I took a second, closer look at your photo. I am now quite confident that this is an example of die fatigue. The most peripheral design elements ride up onto
      Message 2 of 4 , May 5, 2003
        I took a second, closer look at your photo. I am now quite confident
        that this is an example of die fatigue. The most peripheral design
        elements ride up onto the inner raised ring. That indicates that the
        die face was distorted. All the other causes I cited require that
        the peripheral design elements lie inside the inner ring.

        --- In errorcoininformationexchange@yahoogroups.com, "Mike Diamond"
        <mdia1@a...> wrote:
        > Interesting. There are a number of possibilities.
        >
        > The most likely explanation is that the circular ridge internal to,
        > and paralleling the rim is caused by die fatigue. You find similar
        > features developing in our copper-plated zinc cents, although
        they're
        > seldom so narrow, complete, and even throughout.
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