They can be tough. The transparent ones often have fine bubbles, the white gets ruffles in the ribbon under the glass... like undulations or ribs. Hard to describe. The thing that helped me most with sorting out the transparent ones was getting a lot of cullet dug from the factory site, which helps me identify the colors and other traits. CAC made lots of transparent swirls apparently. Some, like the wispy lime green ones, I would never have guessed CAC until I found cullet exactly like it from the factory. I'm not 100% positive on the correct ID of every marble here... I think the yellow one all the way to the right is probably an Akro after a closer look, and there is at least one Alley in the mix too.