If you take a really close look at the left hand side of this insulator, I believe that you'll be able to see the original grey/clear glass it was molded in has not begun to purple like the rest of the insulator. This aspect is easier to see in person with the insulator on a light table, and even then it is subtle. It's an interesting phenomenon - I'd love to hear your thoughts on it. I know for a fact that letting a Whitall Tatum Co. No. 1 turn purple in a window does not require rotating the insulator for even coloration, so this insulator is a puzzler.