⟩ The famous penny black, the world's first postage stamp, was introduced in England in 1840. The idea of postage stamps was a great success and was taken up worldwide. Yet the penny Black was in use for only one year before it was replaced by the Penny Red. Why?
The postmark used at that time was always black. It was therefore difficult to tell whether a stamp had been frankled or not. This led to people reusing used stamps. On a Penny red the black postmark was clearly visible.