Let me call Gary Clark (I talk to him on the phone a lot) and see what's that clear cover is. I'm hoping it's sapphire. Maybe I'll convince him to make it sapphire. It's easier to talk to Gary than the rep factories
I don't use watchmaterial pearl anymore despite its sapphire cover. The rim is yellow and so is the lume. The lume can be rather dirty. But if you need a gold rim pearl, the watchmaterial gold rim pearl is absolutely the best. No dirty or yellow lume issue. It's as if a total different manufacturer made it. Another thing not good about watchmaterial insert is the paint isn't very good, kind of rough and the inside edge is little curved. The "4" isn't accurate either. The "4" is perfect on the wm9, TW inserts, now also on the Clark insert. JewelryOutlet555 has a decent insert for $10 which doesn't have poor paint nor curved inside edge. But the pearl is a simple construction, no clear cover and the "4" isn't very accurate either.
-bk