My observations in 5 cases of 50+ year old slides.

[BradleyK]

My father's Kodachrome slides from the 1950s, 1960s, 1970s and early 1980s look as though they were shot and processed last week; the colors are as rich and vibrant as - I would guess - they day they were shot. His Ektachromes from the 1950s and early 1960s (when he apparently gave up on the film) are of uneven condition: some look almost as good as the Kodachromes; others have a blue cast. Perhaps the determining factor is the quality of processing? His small collection of Fujichrome slides - all shot between 1974 and 1976 - look like s#*t: all have faded to magenta (all are in Fujichrome cardboard mounts). Dad's collection was stored for its entire life in his "man cave" (i.e. his basement den, with a humidity of around 45-50 per cent (humidifier) and a year round temperature of 18-20C (68-70F range, more or less).

[benjiboy]

Which modern alternatives I can use for slide archiving?

None, Kodachrome was unique that's the point.

[bishy]

Which modern alternatives I can use for slide archiving?

There is a suggestion in the Wilhelm Research data, modern E6 Ektachrome films have dark storage fade rates similar to Kodachrome in the least stable dye, however light fading rates below Fujichrome. The data is over twenty years old now, so there may have been improvements made to both ranges of Kodak and Fuji films.

Only time will tell...how stable the modern E6 films will be.

[zumbido]

But, but... I'm always told that film is immortal and only d*****l files spontaneously rot?

[Aristophanes]

But, but... I'm always told that film is immortal and only d*****l files spontaneously rot?

Film = Elves
Digital = Orcs

[L Gebhardt]

I've been scanning slides taken by my grandparents from the 40's through the early 70's. Mostly on Agfachrome, but some Kodachrome and Ektachrome. The Kodachrome looks as good as new. The Agfachrome has a variable amount of fade, with some looking decent, and some pretty bad. It's still correctable digitally. The Ektachrome has mostly gone red, and isn't easily fixable. The Agfachrome does seem to have been attacked by fungus the most of the three types, but none has avoided the fungus completely. Storage wasn't ideal at my grandparents house, or my Dad's where it spent some time in a humid basement.

[Ap507b]

I have a few boxes of Fujichrome that I shot as far back as back as 1986. I can't see any evidence of fading or colour shift in them & they look just as fresh as the Kodachrome that I shot in the same period. I have read horror stories that E6 slides of this age should be quite degraded by this age, but I am just not seeing it with mine.