Magnetic dice (also called electric dice) are, as the name implies, a type of crooked dice that can be controlled by an external magnetic field. Magnetic dice are made on a dice charger.
Most types of crooked dice are percentage gaffs, meaning that they don't guarantee a sure result on every roll, but rather just offer a strong percentage in favor of the operator. This means that any percentage gaff can miss, sometimes even for many times in a row. However, magnetic dice fall into the category of dice that always hit the perfect result, whenever a desired outcome is needed. This being said, it should also be noted that there are three basic types of magnetic dice, depending on how the cubes are charged: one-way dice, two-way dice, and three-way dice.
One-way magnetic dice can only roll one set of numbers, for example, a common set of number would be 2/5. So, for example, if the external magnet is oriented north/south then a 2/5 cube rolls a 2, but if the polarity of the magnet is reversed, then the same cube rolls a 5; hence the name, 2/5 magnetic dice.
By the same logic, a two-way cube rolls two sets of numbers, and a three-way cube rolls three sets of numbers. An example can help clarify this. A cube could be charged to roll 1,2,3 or 4,5,6 depending on the orientation of the magnet. Such cube would be a three-way cube; a set of two such cubes would be used in backgammon, so that the operator can slow down or speed up the game on his rolls and also roll more doubles whenever he uses a magnet.
Once again, magnetic dice are guaranteed to roll certain numbers, whenever the magnetic charge is used. However, in a sense two-way dice and three-way dice can be viewed as percentage props, because although they guarantee that one of the two, or one of the three, numbers will hit, the result within those numbers will still be random.
Magnetic dice have some advantages and some disadvantages over other types of crooked dice.
As we've just discussed, they offer a sure thing, whenever a magnet is used. So, that may be considered a big advantage over percentage props. However, one big disadvantage is that they require more equipment, to be put to use, which is obviously a disadvantage. One usual piece of equipment is a large electromagnet that is usually fitted inside of a table (I've even heard stories of dice mobs going to such extent as to hire a contractor to gig up a sidewalk and re-pave it with a magnetic coil inside, so they could steer a sucker to a predetermined spot, for a back-alley game). The disadvantage of such prop, besides the fact that is is heavy-duty equipment, is that t can be easily discovered if someone happens to place a metal cigarette lighter on the table, or canadian coins, I guess. And I guess the charge from this magnet could stop a pacemaker, so someone may even be facing a man slaughter charge, should anyone die of cardiac arrest in a bustout joint.
Also, one disadvantage is that the dice can easily be discovered, should anyone approach them with a magnet. But the advantage is that any magnetic dice will produce totally legitimate rolls when they are not being controlled by magnets.
Furthermore, poorly-made magnetic dice will actually attract each other, so such dice may be discovered even without testing them on a magnet. This is obviously added to the list of disadvantages.
Another disadvantage is the way magnetic dice behave, when the juice is on. Regular dice roll and bounce freely, and so do magnetic dice, but only until the juice gets turned on. Once the magnet is activated, the dice come to a full stop as if they've completely lost momentum and inertia. So, a trained eye can actually spot magnetic dice just by observing them on a roll.
To circumvent this problem, a mechanic may opt to use a dice cup. In this case the mechanic would rattle the dice inside the cup and turn the entire cup over onto the table, then momentarily turn the juice on and then just lift the cup. This may look perfectly natural in some games, where it is common to use a dice cup, but not on a craps table. So, on a craps table the timing has to be perfect. Also, if the timing is off in a way that the juice gets turned on too late, the dice will seem to perform a miracle that Stevie Wonder could easily spot from across the room, as they will seem to give themselves another spontaneous tumble, after they've already come to a full stop.
Magnetic dice are actual magnet and as such they will attract small ferrous particles, such as metal shavings. Also, if they dice are not made just right, two magnetic dice will sometimes attract or repel each other. Once again, an obvious disadvantage. However, keep in mind that the typical strategy for working with any crooked dice is to switch the gaff in an out of play, as needed. Amateur cheats will rely entirely on the gaff and most likely leave them in for the entire duration of the game, thinking that they are safe. But professional dice mobs will not really allow anyone to examine the actual gaffs. If a sucker is examining the dice, you can be pretty sure they've already been switched.
As a general rule, there is usually nothing spectacular about the appearance of magnetic dice that could be captured in a still photograph, except perhaps hanging from a magnet. Perhaps the most interesting detail to see on a still photograph is the packaging that shows how these gaffs used to be packed when they are sold by the old crooked gambling suppliers.
Below is a photograph of a typical box that was used to package various kinds of dice, not necessarily crooked ones. This particular box does happen to contain magnetic dice and it is also labeled accordingly.
Below is a close-up picture of a pair of casino-style craps dice. Regulation casino dice are not easy to fabricate, as those dice are clear and therefore any standard size loads would be glaringly obvious (which is precisely the reason why one can only find clear dice at a craps table in a casino). However, the magnetic load is so small that it can fit inside the spots of the dice.
If you look closer at this enlarged photo you will easily notice that the white spots are much thicker than they would be on fair regulation casino dice. These spots on these two cubes are of course thicker so that the magnetic loads can be fitted inside. Craps dice can be charged in a number of different ways, but the simplest combination is to make them roll a 7, when the juice is turned on. This particular pair is charged as a 6-1.
The next picture shows a pair of magnetic bird's eye dice. From a technical point of view these are even more advanced than the dice seen above, because the magnetic load is even smaller. The reason why dice makers have developed bird's eye dice in the first place was precisely to make it as difficult as possible to put any kind of loads under the spots. When it comes to magnetic loads, as you can see here, the size doesn't have to be large because a strong juice table will always be able to control dice with magnetic loads, while they are propelling through the air, which has hardly any friction or resistance to speak of. If you look closely at these dice, you will see, just like in the picture above, that the spots appear just a bit thicker than they should. These particular dice are charged to roll 5-2.
I should also mention that these bird's eye dice were made by the legendary dice maker "Junior," probably in the 1990s. When Junior was alive these reportedly sold for $700, now that he had passed away the price of his dice is anyone's guess.
Below is a clipping from an old HC Evans Blue Book, crooked gambling catalog, showing a listing for magnetic dice. The listing shows a general description of magnetic dice (or electric dice, as they chose to call them) as well as a listing for transparent dice, as the ones seen above.
Next photo shows a pair of antique tri-color magnetic dice originally sold by the KC Card Co, from Chicago, Illinois. The handwriting is original from the era and as these dice are just part of my gambling collection I made no attempts to remove the writing. These dice are quite interesting as each cube is charged to roll 1-6 or 4-3 regardless of the orientation of the magnet. To make myself clear, I mean to say that the cube that rolls a 4 or a 3 will roll either 4 or 3 regardless of the polarity of the magnet.
These dice are called tri-color because the spots are made in three different colors (1-6 black; 2-5 red; 3-4 blue). These kind of dice were in use through the 1960s. The spots are made in thee different colors to make it more difficult for dice hustlers to obtain matching fakes. Naturally, crooked gambling suppliers caught up to this and soon began to offer various types of crooked tri-color dice. Due to the fact that the three colors were meant as a security feature, tri-color dice were usually used in high-stakes gambling games.
For further information about magnetic dice and to get an idea about how they are actually made please refer to the dice charger listing.