Marking Cards

Often used for card tricks or to cheat when gambling, card marking is the process of altering playing cards so that the suit, rank, or both are surreptitiously revealed to the card marker or a conspirator. The practice has evolved over the years from adding bends or bumps to cards to using various inks and scratches, and today's card markers use sophisticated "shade" technology to add marks that can only be read with special sunglasses, contact lenses, or what other high-tech system? Discuss


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