"Plexiglass face mounting" means mounting ON the plexi or UNDER the
plexi, face up? Either way, I'm surprised there's been no mention
of plexi discoloring (clouding, yellowing) in time -- maybe not in
5 years, but surely in 15 or 20. Unless there's a new plexi that's
"archival"?
This is a really good point, and even more argument for protecting
the gum by some other means.