Because of the deterioration shown in that dice pair, I do believe that they were made of nitric acid, sulphuric acid, cotton fibers, and camphor, designated as cellulose nitrate and more commonly called celluloid. Just like turn of the Century (1900's) film, cellulose nitrite based materials will deteriorate and there nothing to be done.

The dice you have shown, will never, ever look better than they do and will only continue on a pathway of self-destruction! While some suggest coating them with clear nail polish or other clear coating products, your best bet to preserve any characteristic of them is to take detailed photographs.

As to my "warning"... If you wish to continue possession of those dice, then store them into some sort of air tight container, as they will instigate the same deterioration of nearby cellulous nitrate dice that have not yet started to deteriorate. (Zip-Loc baggies are NOT air tight.)

Note also that NOT all older dice are cellulose nitrate. The chemical mixture was changed to produce cellulose acetate, mid-Century (1950-ish) which does not deteriorate in this fashion.

Lastly, if you collect more dice, be mindfull of the odor of vinegar. That is an early indicator of cellulose nitrate deterioration.

Jim