Bulls eye glass

Discussion in 'European & Other Pocket Watches' started by Les harland, Aug 6, 2017.

  1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.
  1. Les harland

    Les harland Registered User

    Apr 10, 2008
    747
    1
    18
    Hertfordshire England
    Country Flag:
    Region Flag:
    Were the "bulls eye glasses" used in older pocket watches a fashion or was it something to do with the way they were made?
     
  2. novicetimekeeper

    novicetimekeeper Registered User
    Donor

    Jul 26, 2015
    4,821
    9
    38
    retired and on my second career
    Dorset
    Country Flag:
    Region Flag:
    This earlier thread seems to have come to no conclusion. We are used to seeing pontil marks ground out on glassware but that may just have contributed to it as a fashion

    http://mb.nawcc.org/showthread.php?6376-Glass-Bullseye-PW-Crystals
     
  3. Les harland

    Les harland Registered User

    Apr 10, 2008
    747
    1
    18
    Hertfordshire England
    Country Flag:
    Region Flag:
    It is an interesting thread, Thanks Nick
    I tried the Forum Search feature but did not find it because I searched for "Bulls eye" not "Bullseye"
     
  4. novicetimekeeper

    novicetimekeeper Registered User
    Donor

    Jul 26, 2015
    4,821
    9
    38
    retired and on my second career
    Dorset
    Country Flag:
    Region Flag:
    I searched google and that was one of the results.
     
  5. gmorse

    gmorse Registered User
    NAWCC Member

    Jan 7, 2011
    7,202
    22
    38
    Male
    Retired from Xerox
    Breamore, Hampshire, UK
    Country Flag:
    Region Flag:
    Hi Les,

    I believe that it was more to do with fashion, and was mostly a late 18th and 19th century thing, because the earlier crystals were plain, without the ground flat portion in the centre. These high domed crystals were cut from a large blown glass sphere, so pontil marks weren't involved in the manufacturing process.

    Regards,

    Graham
     
  6. eri231

    eri231 Registered User

    Jan 13, 2012
    1,048
    6
    38
    torino italy
    Country Flag:
    Region Flag:
    if I remember correctly, this Liebig image was posted by Tom McIntyre.

    makingcrystalsfront.jpg

    regards enrico
     
  7. John Matthews

    John Matthews Registered User

    Sep 22, 2015
    410
    3
    18
    Retired Systems Architect
    France
    Country Flag:
    Region Flag:
    At the beginning of the C19th given a blown glass sphere how would you produce a watch lens?

    1. set a diamond tipped compass to the radius of the required lens
    2. use a hard pointed implement to create a small indentation in the surface of the sphere
    3. use this as the centre and score a circle with the diamond tipped compass
    4. repeat 3 over the useable surface of the sphere
    5. carefully break out the circular pieces of glass
    6. grind and then polish out the indentations and finish the lens edge
    Result – bulls eye lens.

    Just a thought … I find it difficult to believe it was solely down to fashion and prefer to believe it was in some way related to the manufacturing process – but not necessarily my 'top of the head' suggestion.

    John
     
  8. gmorse

    gmorse Registered User
    NAWCC Member

    Jan 7, 2011
    7,202
    22
    38
    Male
    Retired from Xerox
    Breamore, Hampshire, UK
    Country Flag:
    Region Flag:
    Hi John,

    Your suggestion is possible, but the illustration clearly shows the work being done from the inside of the spheres.

    Regards,

    Graham
     
  9. eri231

    eri231 Registered User

    Jan 13, 2012
    1,048
    6
    38
    torino italy
    Country Flag:
    Region Flag:
    It is obvious that , working from the inside the cut was flat, to be inserted in the bezel.
    regards enrico
     
  10. Omexa

    Omexa Registered User

    Feb 28, 2010
    3,362
    5
    38
    #10 Omexa, Aug 6, 2017
    Last edited: Aug 6, 2017
    Hi John, having worked in the Optical Trade, (Did my Apprenticeship) in the 1950's with E Wood & Co., I think that this method would result in lots of shattered Spheres. In the Movies it looks easy, but it is not. I looked in a Drawer and I still have a Circular Cutter, the Rubber Pad has perished. I might fix it up as I need a Glass for a Mercer Bulkhead Clock that I am fixing up. Regards Ray
     
  11. Tom McIntyre

    Tom McIntyre Technical Admin
    Staff Member Donor Sponsor NAWCC Member

    Aug 24, 2000
    77,850
    396
    146
    Male
    retired SW dev
    Boston
    Country Flag:
    Region Flag:
    The thing that amazes me is that I have seen pictures of surviving spheres with most of the crystals cut from them but the sphere intact. That seems to prove that some of them were cut from the outside.

    I agree with the view that the bulls eye was a fashion trend of the late 18th and first half of the 19th century.

    The other thing one could do to understand this process better would be to measure the height and diameter of some of the very high dome crystals that still exist on the market and are often seen on the early 18 century watches. I suspect that those spheres were pretty small to start with to get the extreme curvature.
     
  12. gmorse

    gmorse Registered User
    NAWCC Member

    Jan 7, 2011
    7,202
    22
    38
    Male
    Retired from Xerox
    Breamore, Hampshire, UK
    Country Flag:
    Region Flag:
    Hi Tom,

    Yes indeed, only around 3 or 4 inches in diameter, or even less.

    It's not easy to make out the exact nature of the tools being used in that image in post #6.

    Philip Priestley wrote an article on the subject in the December 2009 issue of the Bulletin.

    Regards,

    Graham
     
  13. novicetimekeeper

    novicetimekeeper Registered User
    Donor

    Jul 26, 2015
    4,821
    9
    38
    retired and on my second career
    Dorset
    Country Flag:
    Region Flag:
    I love glass, but I'm rubbish at working it. I find the idea of making the spheres and cutting the circles amazing. I've seen watch glasses made by the slump method, such skill.

    I love finding glass in a longcase showing the circular rings from production.
     
  14. Omexa

    Omexa Registered User

    Feb 28, 2010
    3,362
    5
    38
    Hi Tom, that sure must take some Skill.
    Here is a Photo of how we cut different shaped Lens; you put different templates on the bottom View attachment 352727 . We edged on a Sandstone Wheel going away from you in rotation using water on the Stone. We later used Diamond impregnated Wheels. Regards Ray
     
  15. Tom McIntyre

    Tom McIntyre Technical Admin
    Staff Member Donor Sponsor NAWCC Member

    Aug 24, 2000
    77,850
    396
    146
    Male
    retired SW dev
    Boston
    Country Flag:
    Region Flag:
    I am not sure that anyone other than a chemist would recognize the term "watch glass" as a small dish used to monitor the evaporation process of a solution.

    I once bought a watch from a friend who had ground a "watch glass" to make a crystal for a late 18th century watch case. It was awfully thick and I replaced it with a correct crystal eventually.
     
  16. novicetimekeeper

    novicetimekeeper Registered User
    Donor

    Jul 26, 2015
    4,821
    9
    38
    retired and on my second career
    Dorset
    Country Flag:
    Region Flag:
    We use them at school, so pretty much anybody who goes to secondary school in the UK will be familiar with them.
     
  17. Jim Shewchuk

    Jim Shewchuk Registered User

    Jul 31, 2014
    5
    0
    0
    #17 Jim Shewchuk, Aug 8, 2017
    Last edited: Aug 8, 2017
    While sorting some ancient glass crystals that had jumped between bins during a move, I have also encountered the term "Bullseye" used in reference to some pocket watch crystals with a roughly 1cm diameter thicker portion in the middle inner surface. (for "hunter case" pocket watches that had a hole in the middle of the cover to view the time without opening)

    While the re-ground "watch glass" lens mentioned yesterday might not have been appropriate for the watch it got mounted in, it seems that some pocket watch models from my grandparents era were designed for window-glass thicknesses: some of those ancient 20 ligne crystals were 4mm thick with a 60 degree beveled edge.

    Although that is where the term still survives, "watch glass" has not always been confined to the chemical sciences. Some of the older watch parts catalogs from the early 1960s also referred to the smaller domed clock crystals in the 2 inch area as "watch glasses"
     
  18. novicetimekeeper

    novicetimekeeper Registered User
    Donor

    Jul 26, 2015
    4,821
    9
    38
    retired and on my second career
    Dorset
    Country Flag:
    Region Flag:
    watch glasses for use in Chemistry are generally around 2mm thick, just under. We use them in Physics at school as bearings for electrostatic rods.
     
  19. Jim Shewchuk

    Jim Shewchuk Registered User

    Jul 31, 2014
    5
    0
    0
    As are most of the domed mantel clock crystals I've encountered. The 4mm example referred to a super-thick style of pocket watch crystal I had encountered during sorting those mixed-up crystals. (presumably rarely used because any impact sufficient to break one would likely also severely trash the movement)
     
  20. novicetimekeeper

    novicetimekeeper Registered User
    Donor

    Jul 26, 2015
    4,821
    9
    38
    retired and on my second career
    Dorset
    Country Flag:
    Region Flag:
    I've always wondered why they were called watch glasses, they are generally clock sized.
     
  21. Jim Shewchuk

    Jim Shewchuk Registered User

    Jul 31, 2014
    5
    0
    0
    This is just a guess, but since some of the largest pocket watches did come close (I've encountered a single surviving example of a pocket watch case using a 22 ligne glass [49.6 mm / 1.95 inches]) to crossing over into using the smaller end of the clock glasses, I suspect that some even larger examples existed in the distant past similar to today's "wrist clocks". (a local nickname for wrist watches with 40+ mm crystals)
     
  22. novicetimekeeper

    novicetimekeeper Registered User
    Donor

    Jul 26, 2015
    4,821
    9
    38
    retired and on my second career
    Dorset
    Country Flag:
    Region Flag:
    Yes, I think you are right, it's probably a very old term.
     
  23. dshumans

    dshumans Registered User
    NAWCC Member

    Sep 17, 2009
    336
    2
    0
    I always presumed that the true bulls eye crystals were used to let the watch be placed dial down and stay level, and to make the watch a bit thinner. I have a number of old bulls eye crystals and they are from quite thick glass originally, then ground flat from the outside on the top.
     
Loading...
Similar Threads - Bulls glass Forum Date
Pocket Watch glass European & Other Pocket Watches Mar 11, 2015
Should I replace the glass crystal on this 1853 pocket watch? European & Other Pocket Watches Sep 2, 2013
Chipped the glass opening bezel, problem ? European & Other Pocket Watches Oct 17, 2011
have you ever seen a pocket watch with a glass covering movement? European & Other Pocket Watches Nov 2, 2010

Share This Page