Card marking is a well-known cheating method used in many gambling games, especially poker. It involves adding invisible marks to the cards, so that players can read them using special contact lenses or scanning devices. Some of the more advanced marked cards are designed to work with sensors or other concealed technology that make them glaringly obvious for those who know how to detect them yet completely invisible to casual players.
There are a variety of marked poker cards on the market, including IR invisible-ink cards, side barcode marked and contact lens marked. Each type of marked deck has its own advantages and disadvantages. The most common types of marked decks are Copag double decks 1546, Modiano invisible-ink marked cards, Bicycle Ultimate marked card, and Copag 1546 single decks.
One of the most popular ways to mark cards is by block-out. This involves using dyes on the backs to color in small sections. This is a practical and effective method of marking poker cards for magic effects, but the traces are visible to regular players from a distance.
You can easily detect card marking by observing the style of play of a player’s partners. If a player consistently folds when his partner plays a good hand, it is likely that they are colluding to gain an unfair advantage over the banker.