Effect:
The magician takes a long-stemmed glass and announces that he's going to perform an card trick. The thing about this card trick is that he won't be able to touch the cards, because they'll be inside the glass the whole time!
Placing the pack face-out in the glass, the magician states that he's going to find all four aces using special "Locator Cards". He reaches into the glass and pulls out a red number card (we'll use the Ten of Hearts for the example) and puts it in front of the rest of the cards in the deck so that it is the card the spectator now sees looking at them through the glass.
The magician then states that he will let that red 10 find a red ace. Holding the glass by the stem, the magician passes a cloth napkin over the glass quickly. When the napkin has completed it's quick pass, the red 10 has been replaced by a red ace ! The magician then takes the red ace and puts it in back of the deck and passes the napkin again.
This time, the red 10 is replaced by the other red ace! Now the magician gets a black number card (say, 6 of spades) for the "Locator" and puts it in front of the red 10 . A quick napkin pass, and there's a black ace!
The magician takes the ace and puts it in back of the deck. Another pass, and there's the last black ace! Now pull out the pack and put it back in the case, smiling as you take your bow. All of this magic occurs in the glass, so there's apparently no way that you could've manipulated the cards! People will fall down at your feet and worship your incredible abilities. Maybe.
Method:
A slight amount of preparation work is required for this excellent card trick, but this is worth it. First, find a wine or any other long-stemmed glass that will allow you to set at least half a deck of cards in it.
There can be no design on the glass or stem!!! Next, take the two red aces and glue them back to back. Make sure you make them look as much like one card as possible!
Do the same with the two black aces. Now get two identical number cards - one black and one red - from an identical deck. Glue one red and one black back to back. Don't do this with the other ones. Finally, get a cloth napkin that is big enough and dark enough to completely cover the glass.
With this prep, you're set!
Set up the deck like this: The black 6 card face-up on top of the face-down deck. Now, set the double-sided black ace on top of it. Now place the double-sided red 10 /black 6 card with the red 10 face-up. Next, comes the double-sided red aces . And finally, the last red 10 FACE-DOWN on the face-down deck.
The rest is showmanship. Place the deck in the glass with the bottom card facing your spectator. Announce that you're going to do the trick using a red locator card. Pull the red 10 off the top of the deck and put it on the bottom, facing the spectator. You should now be looking at a red ace . Holding the glass by the stem, you pass the napkin over the glass and spin it around so that the ace is now facing the spectator.
It helps if you hold the glass with you fingers rigid and the stem in the first bend of your finger. When you spin the glass, your thumb does the work and your fingers look pretty much the same. Now take the ace and put it on top of the deck.
You should now be looking at the other red ace. Perform the pass/spin again, and your spectator sees the other red ace . Now say that you need a black locator card. Take the red/black card off the top with the 6 facing. When you get to the black aces, if you stick the Ace of Spades on top so that it's the first ace you'll show, you can ask the spectator to name a black ace. Nine out of ten times, they'll say the Ace of Spades!
You then make it appear for them. If they happen to mention the Ace of Clubs, just say "So that leaves the Ace of Spades," and make it appear.