I know this topic has been done to death, but I thought I'd report on an interesting personal experience. Just today I removed from their frames six RC prints of mine, produced in my darkroom on 12 X 16 Ilford Multigrade IV Pearl RC. They have been in frames in our two Philadelphia houses over the past three years, WITHOUT any glass or plexi covering -- because I prefer to exhibit them that way, but also because I had read somewhere online that RC prints can suffer if confined behind a cover. (Something about urban gases being trapped there, eating away at the print surface.) For two years they were hung in fairly subdued light, but this past year they were in a very bright location, with the sun actually shining directly on some of them for a couple of hours a day. As it happens, I have virtually identical prints of these same photos, done at the same enlarger settings and processed in the same way, stored in an archival box. So I compared the prints removed from the frames with these boxed prints. There was absolutely no difference. Obviously, this is a particular set of circumstances, and I realize that RC prints exhibited in other circumstances may show deterioration over time. But I personally have never found any such deterioration, even in my prints done over ten years ago (all on the same paper). YMMV.