Air Post stamps. 1923, black surcharge 10m on Airplane 5m+5m yellow, black and light green, Aeronaut (Paevaleht) original perforation 11½, full OG, previously hinged, VF and very scarce the ''key'' value of the Estonian Air Post, only 300 stamps were perforated (certificate says - 400), T. Loebbering certificate, C.v. $650, Est. $500-$600 (Image)