I have always liked this set of 9 air mail stamps from Mongolia, so I was pretty pleased when I had managed to get all the 9 stamps on the stamps on it. The Mongolian stamp office must have had a penchant for this particular shape - a square put on edge. I don't know if there is a special philatelic term for it. On the pages devoted to Mongolia in the Scott catalogue that shape certainly pops up very often.
This set is neither rare nor expensive. The designs are harmonious and clever: Filigree on each side corner, national emblems on top, and a generic posthorn around the denominations at the bottom. All the stamps in the middle are from different countries and seem to have been picked to illustrate postal communication in different forms, conveying letters by car, by horse, by hearse, by foot, by train, by rocket ... and of course by balloon and reindeer! The occasion for this issue was a meeting by COMECON - The Council for Mutual Economic Assistance - an organization of communist countries led by the USSR, The Soviet Union. That's why we only find stamps from the 'Eastern Bloc' represented, in addition to Cuba and Mongolia.
One of these Mongolian stamps is definitely worth a closer look. It is this one:
Not only is it a stamp showing another stamp showing a third stamp - which is rather rare and Russian dolls-y - it is also noteworthy because the main stamp on it, the brown and green Cuban 50c, doesn't even exist in this color combination. It is in fact a mix of the two stamps I have placed on each side of it. It must therefore be regarded as a pseudostamp. And a curiosity.
The reason was probably that the designer, when the 50c stamp was chosen for its theme (the first experiments with mail by rocket in 1939) found it hard to reproduce a mainly black stamp with a black frame, as the frame on all the other stamps on stamps in the set. Obviously, a black stamp without white borders and perforation will always be hard to distinguish against a black background. So he chose the brown 50c instead. But the silver rocket imposed on the brown one makes the writing on the green stamp in the middle impossible to read and destroys the connective meaning. So he took the most useful parts of each of the two 50c stamps and made up a new and non-existent one. My guess is that the decision to use such a difficult stamp to reproduce was taken by someone else, and that the designer just had to find his own solution. Anyway; every stamp has a story to tell. And some stamps are unfathomable.