This trick was performed by David Blaine on his television special

Effect: The magician takes a cigarette and rubs some of the ashes into the spectators clenched fist until they disappear.
He then says some magic words and asks the spectator to open their fist to reveal that the ash has penetrated onto their palm.

Preparation: Put some ash on your middle finger

Method: Tell the spectator to stand in front of you and hold their hands out towards you, palms down .
Tell them to come a little closer and physically grab their hands to gently pull the person a little closer.
At the same time touch their palm lightly with the ash on your middle finger .
Ask them to close their fists, borrow a lit cigarette which you use to flick some ash on their fist and rub in until it disappears.
You can then say some magic words and ask them to open their hands to see that the ash seems to have penetrated their fist.