[brazzy]

No, that's missing a crucial distinction. Writable CDs and DVDs used to be made with organic dyes, and yes, with BD-R the new LTH technology is inorganic and probably longer lasting.

But read-only media has always been pressed and then vacuum coated with aluminum. No dyes.

And the main component for both is always polycarbonate, which is organic, and probably won't last 100 years. There were some problems with early DVDs where the polycarbonate was not sealed propery, which led to oxydization of the aluminum layer, that's probably what GP observed. And of course that can happen through degradation as well.

In theory, it's possible to make these discs from glass, which should indeed last thousands of years. I've even heard that some glass music CDs were made for Hifi enthusiasts in Japan.

[mapontosevenths]

Not all polycarbonate is created equally, or at least it wasn't in the past. M-discs, for example, are rated to 1,000 years. Most folks only seriously believe they'll be good for a few hundred at the outside, but they WERE tested at 85% humidity and temperatures up to 185 degrees for extended periods of time. That's not the same thing as aging, but it's a pretty good stand-in.

The funny thing is... The rumor is that M-disc and normal discs are basically the same now. They're made on the same line and labelled differently from what I've been told. I can't vouch for it, but it makes sense and I've seen some folks online posted various test results that seem to back that up. The fancy Japanese certified archival discs are the same way. They're made on the same lines, just maybe examined a bit more carefully before packing.

I hadn't heard about those glass discs! Very cool. Now I kind of want one.