This telegraph insulator type 1-1920 has been in use on a telegrpah line along the Genova-Milano railroad. After many decades of use, it got this look, due to the steam locomotives running this line. Day after day, train after train. Quite a witness of a lost age. The insulator is all black also inside, and..... what a smell of coal! Anyway, a good bath of acid could bring it back to the original beauty. Next pic shows the inner part of it.