You may be familiar with marked cards if your interest is in card magic and games of cheating. These are special cards that have discrete markings to help magicians or poker cheaters determine the values and suits they hold. They can also be used to find out the dealer’s secret hand in gambling games such as blackjack.
Marked cards are used since the 14th Century, when playing cards were first introduced. The earliest methods of marking cards involved crimps and bends. Card sharps began altering patterns that appeared on the backs cards to help them identify a card’s value and suit. There were many variations on this process, including bending, crimping and creating tiny pinprick bumps, called “blisters,” that resembled the Braille script.
More recently, with the advent of modern technology, card-marking techniques have evolved rapidly. These include block-out and cut-out works, scroll work, and shade work. Card hustlers add or remove lines on the back of a card using various inks and colors. This allows them to identify the suit and value of a card in a variety of ways, such as by adding a thick line to stand for a number.
A new type was developed: coded system. This type is more subtle than reader systems. It enables you to distinguish the value of a card by observing other visual indicators, such as circular patterns on the back of the card, which correspond to a clock face. If the clock hands on the card point in opposite directions, for example, you can tell if it’s diamonds or hearts.
Currently, there are many different kinds of marked contact lenses, including invisible ink and barcode marked contact lenses. The most popular kind of marked cards is the barcode marked cards. These cards are processed by a barcode scanner to reveal the value of each card on the obverse of the cards. Other players cannot see this information. These are especially useful in card games such as blackjack, where the winner is determined by who holds the highest points (not exceeding 21).
The second type of marked cards is luminous marked cards. These cards have a color difference at the back, which is detectable with a special flashlight or gimmicked glasses. This type of marking is the most difficult to recognize by others, but it can be very effective in magic tricks and poker cheating. It can be used by poker rooms to analyze a game after it has taken place and detect collusion.
Shaded marked cards are another option. They have a different color on the back that can be viewed by other players wearing dark sunglasses. These are most commonly used by magicians. These are not as visible as the luminous markings and require special lenses, or a deck gimmicked glasses.