Here's a big help to bottle diggers..

[Marbleguy]

You folks probably already know about this. But if you don't,here it is http://www.myinsulators.com/glass-fa...ttlemarks.html

[BttleDiggerDrew]

Its funny that you mention insulators, when I was growing up in historic morris county, nj I used to fish the "ye old rockaway river" and I used to see these insulator things mostly in a light blue or green along the iron mine train tracks and in my intemperate days as a "yute" I used to try and skip these across the stream, kicking myself now..