To be honest with you , I myself have a little Ebay shop and a website dealing in antiques. The thought of looking up the marbles I had lying around just came recent to me.
I recently saw something about a marble factory on Discoveries "Hows its made" , I realized then that it should be considered glass-art. I actually believe there's alot hanging around, when I was young (now 28) everyone had a big bag of marbles laying around at grandparents, nobody put any interest in though 😛
Greetz D