1963 · Ultraviolet Stamp Detection · Werk 750 von 1.871

An envelope facing and cancelling machine of 1963 in the cancelling room of a main post office in Dayton in Ohio, a waist-high machine of grey sheet steel two metres long, along its top a narrow channel in which envelopes travel upright one behind another, seen edge-on as a row of pale paper edges, above the channel a small shielded lamp casting a patch of violet light, inside that patch on one envelope a small rectangle glowing orange-red under violet light, two centimetres wide, at the feed end a postal clerk seen from behind in a pale blue shirt with an armful of envelopes, dim even light from fluorescent tubes overhead.