As an experiment, I embedded several frames of highly tinted and toned Nitrate film from an original 1910's film release print in clear resin about 1997 and it shows absolutely no signs of fading, decomposing or deterioration. Of course, I keep out of the sun, but just being trapped in that resin should have detrimental effects, but it doesn't appear to so far. Go figure...
The kit was one of those "make a memento" kits with the resin, a couple of paperweight molds and instructions. Can't remember the brand, but it was pretty simple.