Air Post Stamps. 1923, red overprint ''1923'' or surcharges 15m and 10m on 5m+5m yellow, black and light green, two blocks of four and vertical pair, each one with gutter in the middle, No.C2 and C4 slightly folded along the gutter, fresh quality, full OG, NH, VF (Image)

Air Post Stamps. 1923, black surcharge 10m on 5m+5m yellow, black and light green, full original smooth gum variety, NH, VF, and rare, according to Estonian Specialized Cat. only one or two sheets with smooth gum were produced, expertized by R. Gräffe, A. Rucins and others (Image)