No pics, as I'm sure most people know these marbles. My question is, why is there a variance in how much they react to UV light? Does it tell you something about when they were made? I have 6 of them, and to the naked eye the base glass looks basically identical. However, under UV 2 of them glow intensely, 3 lightly glow, and one does not glow at all. My 2 Milky Oxblood's don't glow either, while my 2 Lemonade Ox glow intensely and my Egg Yolk Ox doesn't glow at all. Just curious as to why and what it means. Thanks!