Jean de Sperati spent his life creating forgeries designed to undermine the most knowledgeable philatelists. Even his book "Philatelie sans Experts" (Philately without Experts) shows his prime motivation was the thrill of creating forgeries that even great experts couldn't tell apart. And Sperati's work is good. So good, in fact, that until about 1920, when it became known that he was doing forgeries, stamps that he made in his workshop would routinely get certificates as genuine from the most prestigious certifying boards.
Sperati's work was a passion. He engraved his stamps from scratch - a process that took months. He bought sheets of genuine stamps so that he could use the selvage for printing his forgeries so that the paper and watermark would be the same as the original. Indeed, one wonders that he bothered at all as the financial gain from producing his work must have been less than his costs and his time, certainly the time of as fine an artist as he was.
Herbert Bloch, the great stamp expertise, famously said that experts never determine genuineness per se, that all an expert can do is compare a specimen against all known forgery types. Sperati, until he announced himself to the philatelic world, had done all his work unknown to philately. And his forgeries were in the finest collections.
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