The polarizing filter reduces a lot. Even so, what I get as you may have guessed. is glass edges and bevel "angles" also hot spots from the gilt frames. Shadow boxes I've pretty much decided to live with somewhat reduced reflection as the shadows are as bad as the reflections.
No front flash, but bounced umbrella for some. Lowel lights with diffusing material for others. This is for insurance "proof" so well focused but less than perfect will do. I'll experiment with some of your suggestions for the next setups. Thanks, Chuck.