An imperforate 15h from plate VI postally used — Košice 2, 13 July 1920
A postcard franked with two Hradčany stamps — a 15 h brick red and a 5 h light green — looks unremarkable at first sight. Yet the KOŠICE 2 * Č.S.P. cancellation with the legible date 13 July 1920 ties a stamp that deserves attention: the 15h is imperforate and, as the plating showed, comes from printing plate 6. The card survives complete; the illustrations below are crops of its franking.
Imperforate 15h sheets are commonly documented from printing plates 1 and 2. A postally used imperforate stamp from plate 5 or plate 6 is, by contrast, a rare occurrence — and exactly such a piece is documented here, with a full date of use.
Plating the stamp
The stamp was attributed by combining computer comparison against a reference library of used stamps (over 11,000 registered copies from all seven plates) with the classical method: a plate classifier first pointed to plate VI (probability 0.99), and the within-plate position model then identified field 34. The attribution was confirmed by point flaws — the constellation of sky dots right of the cathedral and the characteristic dot just left of the tip of the sixth tower.
A curiosity of this franking: the affixed 5h stamp overlaps the right edge of the 15h, so roughly one sixth of the design width was hidden during attribution. The sheet margin with the MUCHA signature survives below.