Thanks Ian, these seem like very important caveats.
Do any of Luis Nadeau's published books cover photoceramics? Perhaps the encyclopedia?
Luis' Encylopedia does mention many combinations and permutations of "photoceramics". Many familiar names appear: Poitevin, Joubert, Garnier and Salmon, Camarsac, Obernetter, and more. One would have to hunt down the patents, or journals of the era to procure the exact formulae and procedures.