Very interesting indeed, much of which I had learned and actively practiced with my framers since 1993. I have always specified Crescent Rag Mat (5 or 9-ply) and TruVue UV retardant glass for exhibiting Ilfochromes under spots. The cost of framing an image like this (chiefly Ilfochromes) has risen dramatically since the start in the early-1990s.

A typo for correction, http://www.framedestination.com/photo_preservation.html

The more this happens, the more the image faces. This process is called photolysis.

~should be fades?