I have this one coming from Belarus, a (CD 568.? ) in blackglass. First one of these that I've ever seen. No manufacturer's marks or other embossing. Photo taken by seller, I will replace it with one of my own, when it arrives. The base color is dark amber, as evidenced by some small surface bubbles and tiny base flakes. Otherwise, the glass is completely opaque to a bright light source. I'm not sure of the CD, I'd guess that it is a mamber of the CD 568.* family, and is similar to many other Russian insulators in shape and size.

Update, 13 Nov 2009:

Apparently this insulator was made by Steklo Zavod Neman (C3H), as it has the old style "Niemen" side notches below the ends of the top cable groove.

I found the follwing information verifying this, it describes a different insulator, but it does explain this physical characteristic and its historical foundations:

"Ink Cobalt C3H russian 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".

So, these "side notch" insulators are from either J Stolle Niemen (Poland) or Steklo Zavod Neman (Belarus).