detail, the petal is washed with a light ink of a similar colour to the card ink. Cut-out Cut-out work is use of a razor to scrape off some of the printed areas of the card, such as adding (cutting out) a white bird to the back design. Shading Luminous marking - These can only be read by using special gimmick sunglasses or by wearing contact lenses. The original luminous systems used red lenses and greenish ink on the back of red cards, though more recent variations use chemicals applied to the cards. Video-luminous marking - Video-luminous cards use marks that can not be seen by the human eye, even 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 by 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. Often such marked decks will only be introduced by the house when suspected colluders are seated. Juice-marking - The marks are only visible when a person is trained to read the marks. No filtered sunglasses are required, although 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