I have been in the AV staging business for 40 years. From 1984 - 1996 I programmed multi image slideshows. These shows were often backed up for safety's sake. In recent years I have been collecting staging gear, and more recently have been given a cache of slide modules, which I have been capturing to video and putting on youtube. Regarding fading slides, I am seeing that a particular 15 projector show I have here, that includes an original and dupe set, look very different. The original is "all good" but the dupe set is badly faded, especially in the black areas of each slide. I have been told that Ektachrome 5071 was the duping stock of choice. I blame that! Here is a video that includes two copies of the show running in sync - the original, and the dupe set. See if you can guess which is which! All of these slides are 45 years old.
Dropbox - master_set_vs_dupe_set.mp4 - Simplify your life
Here is my youtube channel with 20 or more shows, from 3-15 projectors each:
https://www.youtube.com/channel/UCdGRNxsrsI-efMFSjFDmzvg/videos
Needless to say, I hope you subscribe to the channel - I have more of these to restore and capture!
Steve
www.stevenmichelsen.com/AVL