unused Block of Four 6c Ultramarine & Carmine, error of color (C23 var., formerly C23c), double 'TOP' and double plate no. block of four, fresh, hinged in selvage only, stamps never hinged (small natural gum skips), fine, from the original find and therefore signed Oriol, Kessler and Breushig, with 1990 P.F. certificate, ex Grunin, plate no. blocks are scarce, Scott retail $600.00 as singles, plate no. block unpriced photo