Hi Jim!

I like your clamshells...that appears to be an ingenious solution! It keeps each die separate from others, which I didn't realize was important...until I found a couple of "clumps" of dice that were stuck to each other. Hopefully the plastic of the clamshell won't react with the plastic of the dice.

I can never remember the details of dice composition/deterioration, but I do remember that it's basically the same as old movie film deterioration...

From Wikipidia:

By the 1980s, it was becoming apparent that the collections of motion picture heritage were at risk of becoming lost. Not only was the preservation of nitrate film an ongoing problem, but it was then discovered that safety film, used as a replacement for the more volatile nitrate stock, was beginning to be affected by a unique form of decay known as "vinegar syndrome", and color film manufactured, in particular, by Eastman Kodak, was found to be at risk of fading. At that time, the best-known solution was to duplicate the original film onto a more secure medium.[5]

The problem of film decay is not limited to films made on cellulose nitrate. Film industry researchers and specialists have found that color films (made using processes for Technicolor and its successors) are also decaying at an increasingly rapid rate. A number of well-known films only exist as copies of original film productions or exhibition elements because the originals have decomposed beyond use. Cellulose acetate film, which was the initial replacement for nitrate, has been found to suffer from "vinegar syndrome".[14] Polyester film base, which replaced acetate, also suffers from fading colors.

https://en.wikipedia.org/wiki/Film_preservation