Glass blocks UV light. This is why EPROMS were made with quartz windows even
though glass would have been much cheaper. Regular acrylic plastic will block
UV as well, but special types are available that allow
transmission of UV (such as for sun room roof panels and tanning beds).
My other concern with Plexi-Glass, and this could be completely unfounded, is
that would it etch or get damaged by high concentration peroxide?
Not a concern: we'd just build a walled tub of sorts, put in enough
de-yellowing solution to cover the yellowed item in question, and have
the plexi sitting well above it. The solution would never be anywhere
near the plexi.
