Fading has been a problem since the earliest days of photography.
In 1855 The Photographic Society of London established “The Fading Committee”, a title that now seems quaint.
The early photographs often show tarnishing or oxidisation caused by exposure to air. “Albumen” prints faded because of the decomposition of the silver-albuminate compounds. Humidity and light accelerate this deterioration.
Silver gelatine photographs ( from1880), were more stable but also faded due to residual chemicals, oxygen, pollution and moisture.
(Scource- “Photographs of the past-process and preservation” Bertrand Lavedrine).
Modern prints should last well if stored in cool, dry conditions. In general, the colder the storage, the less fading will occur.
The main proviso is exposure to light. All prints will fade in direct sunlight, especially chromogenic colour prints.
The main 2 types of prints are
Chromogenic (or traditional photo lab prints), and Inkjet prints.
Ink jet prints are considered stable for archival quality (up to 200 years), however colour prints made before 1985 have usually faded to some degree.
Since 1985 chromogenic prints have improved longevity but are still behind inkjet prints in this regard.
Copying a badly faded photograph is the first and wisest option. This ensures what is left of the image will still be available. Restoration is possible from this copy by increasing contrast and darkening the the image. Sometimes detail that seems to be missing can be brought back. The technique of using polarising filters and gels can recover detail from photographs affected by “silver mirroring”.