As you can see in this pic, this is a comparison between two old Ginori's insulators used in Italy in the late 1800s or early 1900s (I got the right one from a trade with Bill Ostrander, thanks!). They both appeared in old Ginori's catalogues, the left one was the n#3. Similar to the right one specimens, but in brown glaze, were used in 1892 for the first AC transmission in the world (5 single phase circuits at 5 kV) from Tivoli to Rome, 30 kms, with the oil cup (thanks to Guido Boreani for these infos).