A dark ink cobalt Neman (C3H) insulator, much darher then the standard cobalt blues.

The seller describes it thusly:

"Ink Cobalt C3H Belorussian insulator with the C3H in a circle, lll on side dome and the lower Stolle Notch on side groove. These insulators were the result of the original J Stolle Neiman molds being salvaged and remarked after the Soviet takeover of the glass factories in Poland.

The lower notch is the J Stolle Trademark reminiscent of the era."

This information about the side notches is a good means of identifying the manufacturers some of those mysterious, unembossed "Russian" and Polish insulators. The original J Stolle Niemens often had a simolar marking, but with JSN instead of C3H in the circle, embossed on the side of teh dome.