Part I: Card Game Cheating · CARD MARKING METHODS
Daub (On-the-Fly Marking)
How it works
Daub is a special paste or chemical substance that a cheater applies to cards DURING active gameplay, eliminating the need to introduce a pre-marked deck. The player secretly transfers daub from a hidden container to their fingertip, then marks target cards (typically high-value cards) by touching the card backs. The marks become visible to the trained eye or through special filtered lenses. Daub can be concealed in rings, under fingernails, or in small containers hidden in pockets. The cheater must first identify which cards to mark, then maneuver them to an accessible position before applying the daub.
Where it appears
Blackjack, Poker, Three Card Poker (especially games where players handle cards)
On the record
Daubing has been documented in casino fraud cases since at least the 1980s. In California cases, courts have ruled that daubing constitutes cheating and is a felony. Modern daub chemicals have evolved to be invisible under UV light and only detectable under specific IR wavelengths.
Detection & prevention
The paid halfHow a monitoring room catches daub (on-the-fly marking), and what stops it recurring — written for the desk, not the reader.
Detection · 80 words
Prevention · 51 words
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.