Posted - October 17 2011 : 2:36:34 PM Another early method of "photocopying" was used in the Civil War by Union army Topographical Engineers ( read: army mapmakers ) who needed to make quick copies of a captured Confederate map showing in detail the defenses of Richmond for distribution to Grant's subordinates during his Overland Campaign. They used a tracing of the map as an overlay on light-sensitive photographic paper and exposed it to the sun. The result was a photo-negative, darkened by the sun, leaving the outline of the tracing plainly visible as white lines on the darkened paper. Within 48 hours the map was thus copied and distributed with no camera ( or Xerox machine )!