Grilled Issues of the United States
There you will find out all sorts of interesting things like "Grilled Stamps." And no, we're not talking about cooking up a bunch of stamps on the bar-b-que!
According to Mystic, "From 1867-1875, a method of preventing canceled U.S. stamps from being reused was put into action – 'grills.' The grilling machine, which was invented and patented by Charles F. Steel, used a roller pitted with small depressions (which created a 'points up' pattern) or with small raised pyramids (which created a 'points down' pattern) to break the fibers in the paper. These broken fibers allowed cancellation ink to thoroughly penetrate the paper. This meant even regular pen ink, which was used to cancel stamps at smaller post offices, would be impossible to remove completely."
They go on to say, "Early in the 20th century, noted stamp collector William Stevenson categorized grills by size and shape, and sorted the stamps by 'grill family.'
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