Card marking is the process of altering playing cards such that the suit,
rank or both are only apparent to the person marking the cards (or potentially another conspirator),
usually for the purpose of cheating at cards by card sharps. To be effective,
the distinguishing mark or marks must be done on the obverse side,
which are normally uniform. Card marking can sometimes also be called as card bending;
it is considered to be the easiest way to mark probably.
A cheater marks a card by crimping here.
 Card marking is often used to cheat when gambling or for card tricks, though many casinos,
particularly those in Las Vegas,
punch holes through the middle of cards they sell to tourists to prevent cheaters from returning to the game tables after buying the cards and then slipping the favorable cards into their hands when playing.
Marked cards can be used regardless of who shuffles and deals the cards.
However, some more sophisticated marked-cards scams involve additional manipulative skills to steer the cards into the correct positions once the desired cards have been identified.
Historically, the first attempts to mark playing cards involved bends, crimps and tiny bumps,
which are called blisters (and resemble the Braille script).
Later, when the first designs appeared on the backs of playing cards, cheats began altering the designs on the backs of cards.
Hustlers have tried using various inks, pigments, scratches, etc., to add or remove lines or patterns from the back of the card design.
Some varieties of card marking include block-out work,
cut-out work, scroll work, shade work, tint work, etc.
Here is a simple example of how block-out work  can be done.[clarification needed]
However, more recently, science and technology have also enhanced marked-card techniques.
The most state-of-the-art technologies are variations of shade techniques.[clarification needed]
These new technologies are the most deceptive and futuristic methods for marking cards.
Traditional block-out and/or cut-out
work[clarification needed] have
the disadvantage that they must
be read close-up, because the
marks are small. On the other
hand, another advantage of
luminous and juice marked-card
is that they can be read
close-up or from across a table.
Block-out and cut-out work:
In brief, block-out work is
simply using the same color ink
as the back of the card and
coloring in small white areas of
the card. For example, sometimes
people add ink to the flowers on
the back of a card by making the
petals narrower or blocking out
a bird on the back design.
As far as cut-out work is
concerned, people sometimes use
a razor to scrap off some of the
printed areas of the card. A
good example would be to use a
razor to scrape off the print on
the card. This results in adding
(cutting out) a white bird to
the back design.
Both block-out and cut-out work
are easily detected by using the
gambler's riffle test.
Therefore, professionals use
juice or luminous to avoid
Luminous marked cards - These
can only be read by using
special gimmicked sunglasses or
by wearing contact lenses. The
original luminous systems used
red lenses and greenish ink on
the back of red cards. New
luminous technology, called
Ultra-Luminous, uses far more
sophisticated techniques that
are based upon different
chemical and optical scientific
principles than the original
Video-luminous marked cards - As
stated above, luminous marked
cards are designed to be read by
the human eye with the use of
filtered sunglasses. However,
recently, a new generation of
luminous technology has become
available. Video-luminous uses
marks that can not be seen by
any human being, even if they
are looking through a luminous
filter. The marks can only be
read by using custom-designed
electronics and filters and
displayed on a TV monitor in
another room to a partner. Then
the card values may be signaled
or transmitted to the player who
needs to know.
Video-luminous does not have to
be used for cheating. They may
be used for magic or by a poker
house or person who may want to
analyze a card game after the
fact. If collusion is suspected,
the recorded images of the
marked cards may be played back
later to detect any unusual
play. If a player consistently
folds a good hand when a partner
plays a better hand, then it can
be assumed that collusion is
taking place in the game. Since
these marks cannot be seen by
the human eye, there is no
chance of detection of the
marks, even by knowledgeable
players, during the game. Often
such marked decks will only be
introduced by the house when
suspected colluders are seated.
Juice-marked cards - The marks
are only visible when a person
is trained to read the marks (no
filtered sunglasses are
required, but some practice is
required to read the
marks). Glasses
can be used to make it easier to
spot these marks.
Tintwork or shade - This
technique uses a tint solution
to mark cards, but the marking
patterns vary depending upon the
back design of the cards being
Daub - A special paste is used
by a player to mark someone
else's deck, on the fly, while
the cards are being used during
a game and even while being
watched. This eliminates the
need to switch in a pre-marked
deck of cards.
Juice dust - An advanced type of
daub, it may be used to make an
ad-hoc juiced deck. Like daub,
it also allows a player to mark
someone else's deck, on the fly,
while being watched. The main
advantages of juice dust are
that it will not dull the finish
of the cards and that it works
on both paper and 100% plastic