Penny Black

Great Britain's Penny Black is generally agreed to be the world's first stamp, issued the 6th of May 1840. Meanwhile, others have been proposed as the world's first, depending on whatever your definition of "postage stamp" is supposed to be.  File:GB Penny Black.jpg|the lower right shows a bit of the adjoining stamp, giving an idea of the maximum size of stamp margins for examples not on the borders of a sheet. 

Essentially treated as money, the stamp had several security features to prevent counterfeiting. The design was engraved with engine-turning, each stamp had a watermark. The check letters prevent strange letter combinations from being passed as genuine.

Check letters appear in the bottom corners. With 240 stamps per sheet (totalling one pound), the lettering runs from "A A" in the upper left corner, to "A L" at the upper right sheet corner, to "A T" at the bottom left sheet corner. This method would continue with the later issues using the same engraved design. Any letter combination outside of the "A A" to "T L" range is impossible except for the unissued "V R" official.

There were 11 plates used for the issue, with the first plate in two states. Plating individual stamps is possible but is quite tricky without the rare book by Charles Nissen, The Plating of the Penny Black Postage Stamp of Great Britain, 1840 (1922) or the long-gone online images from it. This has high quality photographs that allow exact plating. Otherwise, there are several references that provide position measurements and the different letters used, but except in some cases, absolute identification is doubtful. So, if you see a plate number given with a stamp, it should be questioned and checked to the best of your abilities; most identifications are wrong unless someone has the Nissen book.

Many worldwide collectors want a Penny Black and used examples are not rare at all. Price depends greatly on condition, basically on margins and heaviness of cancel. Shop around to see what suits you and your wallet or purse. Stamps with small faults might be all you want to spend, but be aware that 60% of a Penny Black is not worth 60% of catalog value like some sellers seem to think. If your initials fall in the range of possible letter combinations, you can try to find one of those.

Unissued official stamp
Also in 1840, a design with "VR" letters ("Victoria Regina") in the top squares was created for use as an official stamp but was never issue. Used examples are from cancellation ink tests or were possibly passed through the mails by jokers.  File:GB Penny Black official.jpg 

Forgeries?
Remember that the genuine is finely engraved. Reproductions cut from stamp albums and advertising close to the correct size have been passed off as Penny Blacks. Cancels can be chemically cleaned off; this can be detected using an ultraviolet light. The official can be forged by removing corner crosses on normal stamps and adding "V R". 

