With just the eye test, can you tell a Sapphire crystal? I have an unusual watch with no history.
thats correct, sorry, shoulda been more specific.......Which - sapphire?
An acrylic watch crystal is a kind of plastic, which has the advantage of being resistant to shattering, but can be scratched easily. Fortunately, scratches can be easily removed from acrylic. Mineral crystal is a kind of glass, which is more scratch resistant than acrylic, but not as as good as sapphire. Mineral crystals are also somewhat better at shatter resistance compared with sapphire. Unlike acrylic, scratches in mineral glass are more difficult to buff out; and unlike sapphire, mineral glass will scratch. In my opinion, the mineral crystal seems to be a poor compromise between the two extremes. A sapphire crystal is indeed made of synthetic sapphire, which is a transparent form of corundum, or aluminum oxide (Al2O3). It is extremely hard (Moh's scale 9), and will resist scratching by most substances short of diamonds. However, if struck sharply and from the correct direction, sapphire will shatter easier than mineral.... And what would those advantages be for mineral?
Not hard enough to not get scratched, but too hard to polish scratches out. Less impact resistant than either plexi or sapphire. Cheaper? Plenty of affordable watches with sapphire... Sorry, just don't see where mineral fits in today's world.
Just like the lenses in eye glasses - it's anti-reflective coating. That's what scratches on sapphire most times, and why many watch companies coat the inside of the crystal nowadays.Then my next question is, how is Sapphire coated done?