On April 15th, 1959 the air mail postage to fellow Socialist countries was standardized at 20 xu. As a result an air mail stamp in the denomination of 20xu was on November 20th, 1959. The stamps were perforated 11.0 and issued in sheets of 100 each.
Here is the mint stamp
Mint block of four
Here is a canceled to order stamp:
Postally used stamp. Postally used stamps are at least ten times rarer than cancelled to order stamps.
Single franking of the 20xu stamp on a postcard from December of 1959 to Hungary. This demonstrates that the postcard and letter rate was identical at the time.
Letter sent from Hanoi to a Student Housing Project in Dresden, East Germany using a single franking of the 20xu value from February of 1960. One month later (March 1st, 1960) the standard letter rate was reduced to 12xu.
Cover front from a letter sent to France featuring three of the 20xu Air Mail stamp plus one of the old 150D Handicraft stamps issued in 1958 in a mixed currency franking. The old stamp was devalued by 1,000:1 so was only worth 15xu. The overall postage hence amounted to 75xu.
Xunhasaba bulletin mailing to England announcing the issuance of the Mars I stamp set of 1963 featuring a block of four of the 20xu Air Mail stamp plus one 2xu Domestic Animal set for an overall postage of 82xu.
Mixed franking of the 5xu value together with the 20xu Air Mail stamp and the 50xu Artit Congress stamp for an overall postage of 75xu mailed from Nghe-An (small post office) to France. The standard letter tariff to France amounted to 50xu so this letter must have been of the second weight level.
Mixed currency mailing from Hanoi to France using one stamp denominated in Old Dong (Handicraft stamp) in the amount of 1,000 Old Dong (worth only 1 New Dong after the 1,000:1 devaluation on March 1st, 1959). The air mail stamp in New Dong was added in the amount of 20 xu for an overall postage of 1.20 New Dong. The standard letter rate to Western countries at the time amounted to 50 xu so this letter must have been of a higher weight level.
Larger than usual envelope featuring one of the 20xu Air Mail and one of the 12 xu Red Criss stamps for an overall postage of 32 xu. Mailed to the well known philatelist Theo Klewitz in may of 1960.
Registration Nr. 100280