Card marking

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Card marking is the process of altering playing cards such that the suit, rank or both are only apparent to the person marking the cards (or potentially another conspirator) usually for the purpose of cheating at cards by card sharps. To be effective, the distinguishing mark or marks must be done on the obverse side which are normally uniform. Card marking is often used to cheat when gambling or for card tricks, though many casinos, particularly those in Las Vegas, punch holes through the middle of cards they sell to tourists to prevent cheaters from returning to the game tables after buying the cards, and then slipping the favorable cards into their hands when playing.

Marked cards can be used regardless of who shuffles and deals the cards. However, some more sophisticated marked-cards scams involve additional manipulative skills to steer the cards into the correct positions once the desired cards have been indentified.

Historically, the first attempts to mark playing cards involved bends, crimps and tiny bumps that are called blisters (and resemble the Braille script). Later, when the first back-designs appeared on the backs of playing cards, cheats began altering the design on the back of a deck of cards. Hustlers have tried using various inks, pigments, scratches, etc. to add or remove lines/patterns from the back of the card design. Some varieties of card marking include block-out work, cut-out work, scroll work, shade work, tint work, etc.^[clarify]

However, more recently science and technology have also enhanced marked card techniques. The most state-of-the-art technologies are variations of "shade" techniques.^[clarify] These new technologies are the most deceptive and futuristic methods for marking cards. Traditional block-out and/or cut-out work^[clarify] have the disadvantage that they must be read "close-up" because the marks are small. On the other hand, another advantage of luminous and juice marked card technology^[clarify] is that they can be read close-up or from across a table.

Shade technologies:

Luminous marked cards - These can only be read by using special gimmicked sunglasses or by wearing contact lenses. The original luminous systems used red lenses and greenish ink on the back of red cards. The most sophisticated luminous system ever made^{[citation needed]} is being sold under the brand names Ultra-Luminous (aka. Black Panther) and Black Predators, and uses sunglasses with dark lenses.

Video-luminous marked cards - As stated above, luminous marked cards are designed to be read by the human eye with the use of filtered sunglasses. However, recently, a new generation of luminous technology has become available. Video-luminous uses marks that can not be seen by any human being, even if they are looking through a luminous filter. The marks can only be read by using custom designed electronics and filters and displayed on a TV monitor in another room to a partner. Then the card values may be signaled or transmitted to the player who needs to know.

Video-luminous does not have to be used for cheating. They may be used for magic or a poker house or person who may want to analyze a card game after the fact. If collusion is suspected, the recorded images of the marked cards may be played back later to detect any unusual play. If a player consistently folds a good hand when a partner plays a better hand, then it can be assumed that collusion is taking place in the game. Since these marks cannot be seen by the human eye, there is no chance of detection of the marks, even by knowledgeable players, during the game.

Juice-marked cards - The marks are only visible when a person is trained to read the marks (no filtered sunglasses are required, but some practice is required to read the marks.)^{[citation needed]} Glasses can be used to make it easier to spot these marks.

Tintwork or shade - This technique uses a tint solution to mark cards, but the marking patterns vary depending upon the back design of the cards being marked.

Daub - A special paste is used by a player to mark someone else's deck, on-the-fly, while the cards are being used during a game and even while being watched. This eliminates the need to switch in a pre-marked deck of cards.

Juice dust - An advanced type of daub, it may be used to make an ad-hoc juiced deck. Like daub it also allows a player to mark someone else's deck, on the fly, while being watched. The main advantage of juice dust is that it will not dull the finish of the cards and works on both paper and 100% plastic playing cards.^[clarify]

[edit] Detecting marked cards

1) Perform the "gamblers riffle test". This test basically allows a person to detect most marked decks by simply riffling the cards. Looking at the back of the cards while they are being riffled, the marks will dance around the back of the cards like an old-fashioned cartoon. The riffle test is less effective for detecting cards marked with luminous and juice.

2) Reflect light off the back of the card. Cut-out-work (scratches or white ink) will display, as well as many inks or solutions tend to dull the finish on playing cards because they are alcohol based. Only the highest quality solutions will not burn the finish of cards. Placing a drop of alcohol on a card then looking at the finish by reflecting light off the back reveals the burn/dulling effect that these cheap solutions can cause.