These insulators are not overly rare. The first one I found was given to me by Boston Edison in 1967. These are really cool looking wet-process pieces. They have lightly visible concentric rings under the glaze from spinning during manufacture. They are are caramel to light brown in color and are triple petticoat. I am not sure of the manufacturer. My best guess would be that they are Trenton pieces.

Click "Next" for a closeup look at the top of the pole in the foreground.