The card marking is a very useful tool in the magician’s arsenal. It allows them to see the value of each individual card without having it turned over. Some cards are marked and others the entire deck. Depending on the way the deck is marked it can be used to cheat or simply make magic tricks more efficient.
Marked cards can also be read using the old-fashioned riffle method (also known as the “movie flip book” test), where the cards are quickly flipped through, like a movie flick book. Any differences should be obvious very quickly. But it’s also possible to identify cards that have been marked with more advanced methods like juice and luminous marks.
The oldest forms of marking cards included crimps, tiny pinpricks, and bumps that looked like Braille script. But today’s cheats use a variety of inks and pigments to alter the cards’ back designs, often in complex patterns that only they can read. One of the most sophisticated methods of marking cards is called “juice.” It has a subtle, but detectable effect.
A peek device is another gimmick which allows a cheater to see the marked cards by looking through a specially-designed lens. These gimmicks, which are not allowed in sanctioned card tournaments, are commonly used by professional cheaters and can be very effective.