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Question About Concave Crystals

  1. Modest_Proposal Trying too hard to be one of the cool kids Oct 13, 2017

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    When I first saw a pocket watch crystal with a concave dimple , I just assumed it was gouged by an unfortunate accident. But I later found other examples with the same pattern... and I really can't explain them. I only ever find them on older pocket watches. Thoughts?
     
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  2. gwzymytk Oct 14, 2017

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    http://www.pocketwatchrepair.com/how-to/crystals.php

    Apparently they are called "High-Dome Bullseye Crystal", either English-style (earlier, late 1700's-early 1800's) or American (later - early 1900's).
    It also seems nobody knows for sure what their purpose is...
     
  3. Tony C. Ωf Jury member Oct 14, 2017

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    I have seen them, albeit rarely, on wristwatches as well.
     
  4. TropicConnie Oct 14, 2017

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    I suspect it's something to do with the manufacturing process, like antique crown glass window panes.
     
  5. Archer Omega Qualified Watchmaker Oct 14, 2017

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    I don't believe there is a consensus on the nature of the Bullseye crystals. Some believe it is an artifact of the manufacturing process, and some believe it was just a style that was popular. I personally don't believe that it was part of the manufacturing process - I have yet to see a convincing argument supporting that idea. I think it was just a style.

    Cheers, Al
     
  6. Archer Omega Qualified Watchmaker Oct 14, 2017

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    Seen that explanation, but still not convinced personally. If the stem were used to spin the glass and grind it round, then I would not expect to see so may off center bullseyes...
     
  7. Tony C. Ωf Jury member Oct 14, 2017

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    Nah, I'm not going for the spun-glass explanation, either. I've owned a wristwatch from the '50s with this type of crystal.
     
  8. Canuck Oct 14, 2017

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    Post deleted. So many “experts”! ::facepalm2::
     
  9. jimmyd13 Oct 14, 2017

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    I too have seen these and simply assumed they were a "fashion" carry-over from the half hunter cases?
     
  10. Tony C. Ωf Jury member Oct 14, 2017

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    I don't think that anyone is claiming to be an expert, but why on earth would such an anachronistic and expensive process have been used as recently as the mid-20th century?
     
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  11. Deafboy His Holiness Puer Surdus Oct 14, 2017

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    Maybe these glasses were meant for half-hunter type watches. Used to magnify, like a Rolex Cylcops.

    [​IMG]
     
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  12. Canuck Oct 14, 2017

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  13. Archer Omega Qualified Watchmaker Oct 14, 2017

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    I understand completely the process involved in glass blowing, and have many objects of blown glass with the pontil mark. That really isn't the problem with this explanation - what no one has satisfactorily done in my opinion is make the direct connection from glass blowing to the crystals shown by the OP.

    As Tony points out, making crystals this way in the mid-20th century doesn't make a lot of sense. Until that can be explained somehow in a more concrete way, I'm not ready to accept that as the reasoning for this style.

    Cheers, Al
     
  14. Canuck Oct 14, 2017

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    None so deaf as those who refuse to hear!
     
  15. Archer Omega Qualified Watchmaker Oct 14, 2017

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    I agree completely...
     
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