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Using Marked Cards To Cheat At Blackjack Game

For as long as card games have been played for real money, people have tried to get an advantage. Various techniques have been used, including dealing from the bottom of the deck (and other card mechanics tricks), palming cards and marking cards. In blackjack, you would not have to mark very many cards to gain a significant advantage.

This article looks at the different ways in which marking cards has been carried out historically. Information on how the casinos counter card markers, and the small amount of cards which would create an advantage in blackjack if they were marked is also discussed.

How Cards Were Marked – From Ancient to Modern Times


There have been some creative ways to mark cards over the years, with the latest technological advances used along the way.

Blocking is the most common method. This involves making changes to the pattern on the back of a card by adding a colored section where the card was previously white. This could be as simple as filling in a single petal on a rose, or just making one line thicker than the others. In blackjack, if you can see the dealer’s down-card is a 5 (for example), then you can adjust your own betting to account for this.

Cutting is the opposite of blocking, this involves removing some of the pattern from the back of a card – usually with a razor. This can be a minor component for example the wing of a bird. Only people knowing what to look for would spot this during normal play.

Damaging certain cards, by scratching them, pricking them with a pin or bending them slightly is another way to mark cards. In a casino these will quickly be replaced, combined with the risk of getting caught, this makes damaging cards a less desirable method.

Physical changes to the back of cards do require that the cheats have access to the deck before the game begins. This is also easy to spot by ‘riffing’ the deck. If you flick through all of the cards quickly, then any pattern changes should jump out since the backs of the cards will jump around.

Card Marking Ink

Invisible ink has been a favorite way of marking cards for many years. There are several types of this ink available, with the most common varieties requiring special sun glasses or contact lenses to see the marks. There are now more modern inks which can only be seen by computers, these are more likely to be used to catch cheats than for the purposes of cheating by individuals.

In the US blackjack game the dealer has 2 cards (in Europe the second card is dealt after the players have acted). This means that knowing the value of the hidden card would be a big advantage to the players. For example, if the dealer shows a 6 and you know that the hidden card is a 10, then you would adjust your own strategy to avoid busting (since the dealer is likely to do so). If the dealer shows a 10 and the hidden card is a 10, then you may as well take the risk and take another card. Note that if you play too far from a standard strategy, experienced dealers would suspect something is up and may watch you more carefully.

Other methods of daubing cards include dusting them or adding citrus type substances which would only be seen by someone who knew what they were looking for. It should be noted that unlike card counting, marking cards is illegal. You could be indicted and even jailed if caught doing this in a casino.