373rd Heinrich Köhler auction - Day 1

The "Admiralty" stamp with manuscript "3" in mixed franking with "Porto-Piastre" label with manuscript "2½" on folded letter from Constantinople to Chio (Kemlek) with black "POSTA DEI PIROSCAFI OTTOMANI COSTANTINOPOLI P.P." alongside, vertical fold affecting "Admiralty" stamp, some minor ageing, otherwise a fine and exceedingly rare entire with only one other "mixed" franking between "Admiralty" and "Porto-Piastre" recorded, certificate du Vachat (2009)
Provenance: Robson Lowe (1977)
extensively described and depicted in S. Ringstrom and H.E. Tester "The Private Ship Letter Stamps of the World - Part 2" page 121-126