A tak chcialem miec racje 🤮
Dave's Watch Parts and Tools - Regular Bullseye Crystals (daveswatchparts.com)
Tutaj wypowiedz z Nawacu
Glass "Bullseye" PW Crystals | NAWCC Forums
According to the research we did in preparation for our talk, watch glasses, commonly called "watch ctystals", began to be made shortly after 1600 A.D. The first watch glasses were made by blowing a glass sphere. These crystals were all high domed.
There is currently some controversy as to whether they had a "bullseye"(thick flat center)or not. Most written references indicate the first watch glasses had a "bullseye" for the reasons Jerry indicated in his post. However, some prominent present day British horologists think not. Since all of the people who were there are long gone, we will never know for sure!
About 1800, watch case styles changed from pair-cases to single cases that looked like pair-cases. This was an intermediate step to the conventional double backed pocket watch case of the 19th century. Also, thanks to improvements in manufacturing methods, the glasses fitted to the cases changed from the high domed glass to a thinner less curved glass.
If anybody has a written reference pertaining to the "bullseye or no "bullseye" theories, we would appreciate hearing from you.
I agree with Oliver and others, who say that early watches had plain high domed crystals, and that the "bull's eye" type came into style and went out again a few decades later. Oliver may be correct in the timeframe he suggests (1780-1820), but I think it was a bit later than that. I think the prime popularity of "bull's eye" crystals began about 1790-1800, and ended about a half century later. Furthermore, like "pair cases," I think "bull's eye" crystals were much more popular in Britain, than they ever were anywhere else.
Regardless of what some "authorities" claim, I don't think the "bull's eye" had anything to do with assisting in the manufacturing process; I think it was merely for style, and nothing else. Some relatively modern references indicate that the "bull's eye" spot was ground to facilitate mounting on mandrels to grind the edges round, but that idea fails to consider that rather than grinding each and every crystal with a flat spot, it would have been much easier and more efficient to use mandrels that were slightly concave, and fit the natural curve of the glass.
I've looked through my "library" quite a bit for an authoritative source for this information, and I can't find it again at the moment, but I had an occasion to research this subject fairly extensively a few years ago, and I was eventually satisfied I'd found the correct information. I have a 1780s French "pump-type" repeater, that's unusually large, and I was having a devil of a time finding a bull's eye crystal for it. At length, I discovered that watches of that era weren't necessarily intended to have "bull's eye" crystals, and the plain high-domed crystal I was trying to replace was indeed appropriate. "Bull's eye" crystals may have been available at the time my repeater was produced, but they actually came into vogue a bit later.
In any event, you may be certain that "bull's eye" type crystals enjoyed relatively limited and short-lived popularity, and that they're not appropriate for very significant percentage of watches that survive today.