"Erotica has been a very important part of watchmaking history from when we first started with pocket watches," Chris Del Gatto, consultant to high-end jeweler Jacob & Co., tells CNBC. "In the beginning, people would commission pocket watches with faces of their wives or lovers because oftentimes people were separated for months or years at a time."
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Unless you're a serious watch collector, you probably haven't heard of these titillating timepieces. Hand-painted and very detailed (oftentimes extremely graphic) images are hidden behind dials in watches.
For centuries, portable porn has been carried around discreetly, but with a simple twist of a knob, an original erotic scene was revealed. And this "pricey porn" only gets more expensive with age.
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In March 2011, a dentist and self-proclaimed "erotica artifact collector" auctioned off more than 33 erotic watches and animated objects in Switzerland. Twenty-six of those objects were watches that sold for more than a total $750,000.
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The auction house, Antiquorum Auctioneers, says "about 90 percent was sold to Chinese collectors over the phone or the Internet." One Chinese bidder couldn't get enough, taking home 10 triple-X watches.
The highlight of the Swiss dentist's erotic collection? A rare 18-karat gold, enameled pocket watch from 1810 with a concealed, animated erotic scene that sold for more than $220,000.