Jimmy! Brilliant!
a bit more looking around on what exactly ebonite/vulcanite is (just hard rubber, 'vulcanized' apparently) and I'm thinking that's exactly what they are. some other pictures I've found of how it looks when it oxidizes and specifically the fact that one of the pictures said it had only happened under a bath of very hot water - that has to be it, because they sure don't smell like celluloid (another smell quite accustomed to, due to my employment in the 'R&D' dept of a major manufacturer of guitars).
thanks!!