Hard to say....but the detectives are hard at work here ....lol
Keith -- try the bright light again at different angles. So the lettering is right even with the light, and not on any angle at all. Try this under the light both with the flash, and without the flash -- as sometimes the bright light, and the Flash will help to pick up the marks under the heavy glaze....
Even try a UV light -- I mean, why not...see what happens....
If you do like me -- when I do this under a real bright light (about 4 -6 inches away) and take several (several shots) at lots of different angles...with flash, and without flash...then I load them to the computer to look through them better, than reviewing them on the screen of my camera.
Gosh, sometimes when I do this, I have taken like 25 pics -- but then I load them onto the Computer and go through them all -- as I can tell better WHAT the camera pick up than my EYE did.
have you tried taking a pic close to the light, with a Magnifying glass held up to your camera (like I have done here, and on GMB)?? I know a person needs like 8 arms to do it -- but might be worth it....
Looking forward to seeing what you get....