A postage stamp error is any of several types of failure in the stamp printing process that results in stamps not having the intended appearance. Errors include use of the wrong colors, wrong denominations, missing parts of the design, misplaced or inverted design elements, etc. The term "error" is typically reserved for obvious failures in the production process that (potentially) replicate over many stamps; unique errors or poor quality known as "freaks" or "oddities" (see errors, freaks, and oddities). Printing plate flaws, such as cracks, wear, or even constant flaws, and plate repairs, such as re-entries, are also not considered errors.
Genuine errors are uncommon or even rare; postal administrations have several layers of quality control and inspection, and most printing problems are addressed before the stamps ever reach the public. A particular error may only exist in a few dozen copies, and some well-known errors, such as the Treskilling Yellow, are unique (so far as we know). They are prized by collectors, with some fetching prices thousands of times higher than the normal stamp of their type.
Errors are known at every stage of production, starting from design, to engraving, to replication of the die, to printing itself, and to perforation. (In theory gumming errors are possible, in practice used stamps have no gum, so any error would become undetectable).
The following is a list of the major types of errors.
Design error: The picture may be of the wrong subject, maps may show wrong borders, the inscription may be factually wrong, text may be misspelled, etc.
Value error or substituted subject: A die composed of multiple elements has the wrong elements mixed together, as for instance a low-value denomination being used on a design intended only for high values.
Omission error: Part of the stamp's design is missing.
Invert error: Part of the stamp is printed upside-down.
Color error: Stamp is printed in the wrong color(s).
Paper error: Stamp is printed on the wrong type of paper which, e.g., may have a different watermark or color than intended.
Imperforate error: Perforations are missing on one or several sides.
Since that day, it has become a bad habit : each time I look at a stamp, postcard or cover, I check it for errors. And in more that 30 years, I have found and collected more than 3.500 philatelic items, with at least one thing in common:
"the crazier the error,
the more I like it".
In the next pages, I am proud to present you some examples of my collection. You will soon be convinced that, in philately, more than anywhere else, Murphy's law is applicable too !
