Marked playing cards have secret markings on the back that help magicians or poker cheaters identify the suit and number of a card accurately and quickly. These markings can only be seen by specialized scanning cameras, contact lenses or glasses. They are invisible to the naked eyes. These devices are called card readers and are often used in magic shows or poker tournaments.
There are many ways to mark a deck of playing cards, but the most popular is by blocking out certain parts of the cards. This can be achieved by colouring or scratching away a small section of the back of the cards. By tinting, you can also make certain segments of a back card lighter or darker. This method can be more subtle than blocking and requires skill in executing.
A deck of cards can also be marked with luminous markings, which are visible through special glasses. These are usually a mixture of chemicals and juice. This technique is less effective because some cheap solutions dull the finish on a card back.
Luminous reading glasses are one of the most useful and practical poker cheating products. These sunglasses look like normal ones so they are hard to suspect by other poker players. These poker glasses have a metal-framed frame and energy-saving lens to work under different lighting conditions. Wearing the luminous glasses in front of your eye and looking at the back of marked cards is all it takes to use them.