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.