Gaffed Blackjack Prism Shoe
A prism shoe is very similar to a rough-and-smooth shoe. Both of these types of shoe enable the dealer to deal seconds, except that a prism shoe does not require the use of marked cards. Both shoes are typically used to cheat at blackjack, when the house is cheating their players. Although you are not going to find these gaffs in any of the Las Vegas casinos (at least not nowadays) these shoes are commonly used in underground gambling dens, so-called bustout joints.
The image above shows the shoe with the first card pushed back in holdout position, which facilitates second dealing. The position of the top card is not very obvious due to the use of border-less playing cards. Also, when the shoe is in use, the dealer would obscure the front of the shoe by holding the hand over the front, whenever the top card is either in peek or holdout position.
It should be noted that there are two possible cheating positions for the top card. As mentioned in the previous paragraph, there is a "peek" and a "holdout" position.
The peek position is just slightly higher than the regular position. In that position the edge of the top card enters the prism and the image is seen from the rear. This is visible in the photo below. However, this position does not facilitate second dealing.
The other position is further upwards. That is when the card is pushed all the way into the prism and gets jammed inside of the holdout clip. In this position the card is secured, so that the dealer can deal seconds without worrying that the second card will cause enough friction to pull the top card along with it. This position is seen in the first photo, but the photo below shows a clearer close-up.
The shoe pictured above is a non locking prism shoe. This means that the shoe is not fitted with any kind of secret lock that disables the gaff and makes it appear normal.
In my opinion a rough-and-smooth shoe is by far superior form a prism shoe, for several reasons. First of all, the dealer is likely to deal a much smoother actions, since he has less information do deal with. When a prism shoe is in use the dealer may be tempted to peek at every single card (definitely the wrong way to go about it) and thus end up dealing too slowly and in a way that is likely to raise suspicion. Also, in the event that a gaffed shoe is ever examined, even a person that is completely clueless about how these gaffs work can figure out that the prism is a cheating gaff, but an opaque holdout clip on a rough-and-smooth shoe is much more inconspicuous.