Most of my Kodachrome 25 slides have been fairly stable after 35 years. However the once highly regarded Perutz C18 slides have really packed up. Blues have gone altogether and some resemble a feeble attempt at sepia toning. This was evident after only 20 years in some instances.
Thank you all for this discussion and the advice. I need to buy something to copy thousands of slides and 24 x 36 B & W negatives to digital - pity about my 2 1/4 square mono negatives. Digital devices to handle these formats seem to be well out of my price range as far as I can discover. I've still got my enlarger and all the associated gear, but the idea of building another darkroom does not excite, and I've gotten over the smell of fixer many years ago.
Regards,
FOR