If you have any interest in foreign insulators, you must visit this site. Fantastic. Mostly Russian but many other countries are included. This is a link to an English translation of the site. Be patient as it has to be translated. Also, if you intend to make contact and expect a reply, please be considerate and do it in Russian. It is a Russian site after all.
This is just one of the dozens of pictures. There are many drawings as well. Hand sketches, factory prints. You will be a long time finding a better source of information.