Ron, I've been hearing that some one color ones maybe could technically be counted as Opals because they seem to be from the same glass in the same time frame. But being only one color they wouldn't be that desireable to most - not worth mortgaging the dog. (hehe, sorry dog lovers ;-)
Mostly I'm interested for academic reasons. Wouldn't want to be responsible for making people hopeful that their single color patch marbles are suddenly opals. Or for a sudden ebay craze where phantom conquerors get called opals. lol.
I understand that it is a private collector's name which caught on fast, and relatively recently. It's really hard to talk about a private collector's name for marbles as if my opinion matters. That's so presumptuous. It's THEIR name. But I'm me and I still have a lot of ideas. Can't help it. ;-)
Things I wonder: were they made Pre-WWII, using nice pre-war glass? Or were they made Post-WWII, when wartime rationing was over and Vitro felt they could once again afford to use good glass. Structurally, I can see similarities with different eras of Vitros. These seem like serious fence sitter marbles.
That's just a taste of what I'm wondering about. I'll save you guys the rest of my mental meandering but I reserve the right to continue this topic later! LOL.
This has been some pretty good info so far. Thanks for the pix everyone! -s