Part I: Card Game Cheating · CARD MARKING METHODS
Block-Out Work
How it works
Block-out work involves using ink of the same color as the card back to color in or alter small white areas of the back design. For example, a cheater might narrow the petals on a flower design, block out a small bird image, or fill in portions of the border pattern. The marks are subtle and require close inspection to detect. Different blocked-out areas correspond to different card ranks and suits. This technique requires skill and precision to avoid making marks that are obvious to casual observers.
Where it appears
Poker, Blackjack, any game where marked cards can be read
On the record
Block-out work is one of the oldest card marking techniques, dating back to when printed designs first appeared on card backs. Block-out work was listed among marking methods sold by US gambling-supply houses by the 1930s and skilled work can be very hard to spot.
Detection & preventionADVISORY
The paid halfHow a monitoring room catches block-out work, and what stops it recurring, written for the desk, not the reader.
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Published as a detection reference for surveillance, compliance and gaming-operations professionals. Thresholds and tuning are set by the property. Nothing here is instruction: the method is described so it can be recognised.