How to Test a Deck of Marked Cards
A deck of marked cards or numbered cards can be very useful for magicians. They allow you to strengthen existing tricks and open up new possibilities. It’s important to remember that if you use marked playing cards in an inappropriate way, it will ruin the experience for your audience. It’s also possible that your spectator will notice and alert the other players about your cheating. This can cause tournament delays.
The best way to check for marked cards is to riffle the deck and look at the back of each card. If the cards are marked there will be areas on the cards which are lighter or darker than the other sections, or a marking pattern will be more obvious than a standard poker card back design. This method is not able to detect all types. Some luminous mark systems, for example, require special glasses or contacts to be seen.
Another method for testing for marked cards is by examining the cards’ edges and corners. If the sleeves of your deck show signs of wear and tear, you should be suspicious. Check for any signs before playing a game.
As long as the deck is used correctly and does not violate gambling laws, it is legal to use a marked card for magic. It’s never a good idea to use a marked deck in a game for money, as it’s essentially a form of cheating, and the integrity of the game is damaged by it.