1937 Geological Congress

Special Event postmarks of the USSR can be fun to collect, at least as far as the pre-war period is concerned. The one aspect about them that I have trouble with is that they tend to occur on blatantly philatelic covers. Ick!

This cover is icky for another reason: the spectacularly acidic glue that was used to affix the registration label securely discolored the paper of the envelope around it. Ick! But this particular postmark is uncommon so one can be flexible...

But the best part of this envelope is the vertical pair of the 15k Gor'kii stamps: imperforate! Clearly a philatelist was at work here...