There have been questions in the past about Uranium in insulators. Those seem to be few and far in between, BUT…after checking my insulators, battery jars, glass in general of an older age, I've found that the majority contain manganese.

Uranium glows well at 395nm UV, but not so much with manganese. It will, however, glow brightly under 365nm UV.

Below are two insulators, of different colors in regular white light. The following photo is under 365nm UV.