Throughout the Nineteenth Century, postal officials around the globe had one paranoia in common: they feared that postal patrons were soaking used stamps off envelopes, washing the cancellations, and then reusing the stamps. Philatelists who have studied thousands of stamps from the period have found scant evidence of this fraud. But that didn't keep postal authorities from devising more and more detailed plans to discourage such illegal reuse. The anti-reuse hysteria reached its apex with the grilled issues of 1867.
Grills are tiny cuts made in the paper of a stamp. The stamps were printed, gummed, and, before the perforation process, fed into a device that looks like a printing press but which has metal cutting heads that make a small group of slits in the back of each stamp. The purpose of grills is to allow the canceling ink to penetrate more deeply into the paper, making washing agents less effective at removing cancellations, which, in turn, makes reuse more difficult. Since grilling US postage stamps was a solution in search of a problem, there is no evidence that they made reuse less common because reuse was virtually non-existent anyway. But it did create some of the most difficult United States philatelic collecting items to identify, created many rarities, and needlessly increased the complexity of an already difficult era to collect.
There are ten basic grill types, and many stamps come with different grills with the grill alone being what distinguishes the Scott catalog number. The simple 3 cent stamp of the 1861 issue (Scott #65) exists in numerous grill types and ranges in value from a couple of dollars each to a variety that catalogs a cool $1 million.
There has long been a group of US collectors who have collected our stamps in a simplified manner. They have ignored grills on the basis that they were added on at the end of the stamp production process. Such a view is not popular now, but collectors can see the result of this philatelic battle that was fought over a century ago in the fact that the very rare "Z" grills have Scott catalog numbers with capital letters in addition to numbers (Scott # 85A-85F) showing that the original catalog editors didn't know or care enough for the existence of these different grill types to even number them the way they number normal stamps.
There has long been a group of US collectors who have collected our stamps in a simplified manner. They have ignored grills on the basis that they were added on at the end of the stamp production process. Such a view is not popular now, but collectors can see the result of this philatelic battle that was fought over a century ago in the fact that the very rare "Z" grills have Scott catalog numbers with capital letters in addition to numbers (Scott # 85A-85F) showing that the original catalog editors didn't know or care enough for the existence of these different grill types to even number them the way they number normal stamps.