1 Mark Gelber Hund on 10 penny airmail stamp, variety \"double overprint in yellow and blue\", cancelled \"airmail on the Rhine and on the Main Frankfurt (Main) 13.6.12\", faultless condition, issued only 100 pieces - so far are only 34 pieces registered, the overprint war initially in yellow prepared, war but crabbed and war then after all in blue overprint colour executed, the with yellow overprinted sheet got also the blue overprint, photo expertize Mary Brettl International Association for Philatelie Experts (2022) : \"in perfect condition. Very scarce Airmail-rarity. \" by Michel as single stamp not time indicates!