If it is indeed glued on, it could either be Methylene Chloride to dissolve
the glue but that needs to be done in a sealed bottle as it takes a while to
make an effect.
Your best place for optical cements and so forth really is someplace like
SCI.OPTICS where they deal with glass and so forth regularly.

--
Bob May
Losing weight is easy! If you ever want to lose weight, eat and drink less.
Works evevery time it is tried!