Jamey,
I read this thread again, and it has previously been helpful when I was writing about Prosser beads. I feel I can confidently distinguish Prosser beads from ceramic beads. I got these wrong at first, but am now pretty certain they are not Prosser, but ceramic.

In the period that Prosser beads have been made, I believe that the ingredients have varied between periods and manufacturers. Some more clay, others more silica. This makes some Prosser beads look more like glass, while others look more like ceramic beads. However, as is also pointed out in the discussion, they are still a different product than both glass and ceramic.
Interesting to note is that at the time of production, a lot of Prosser beads were marketed as 'porcelain beads', which makes it even more confusing.