I forgot about that page in the Sick catalog. If the term vulcanite passed into a generic usage for all types of hard plastics, then it's easy to see why people even today would call all sorts of hard opaque plastic beads, especially the thin disks, "vulcanite".

It's hard to believe that the disks I have are as old as 1930, so now I'm even more curious about what plastic or rubber they are made of. Although, vulcanized rubber is pretty durable stuff.

Joyce, the disks that seem to stick together may indicate that they are a different plastic than the ones that don't (different surface tension). Many of the disks on my strand are very stuck together but I figured that was due to the dirt on them. I also have on the same strand, disks that are extremely discolored and others that look perfectly clean. Good thing there are so many on the strand since several are going to be sacrificed to the beadology gods.