Lot 50621 – Switzerland, Winterthur – 1850 2 ½rp, glass support

Switzerland, Winterthur – 1850 2 ½rp, glass support cliché of background with reversed image, showing what is red in the original stamp, with notation « cuivre sans verni » (unvarnished copper) and indication about the light « B.L. » over the screen which was used for the two minutes and thirty seconds exposure, “2’30″ ».