Several assorted black faced cards along with one diamond card are shown
on both sides. Let us say the diamond is a 10.
The 10 of diamonds is placed face down on a table. The black cards are
shown again without the 10D, but suddenly the 10D reappears among the black
cards. This is repeated over and over again. Each time this happens the
10D is placed face down on the table, leaving less black cards.
Finally, there are 3 black cards left in the magi's hand. Then, all but
one of the former 10D's are turned over on the table.
To everyone's surprise all the cards on the table are black, except one.
The first 10D that was placed on the table is the "diamond in the
rough." It actually has 10 diamond like stones on the face of the
card. This is a gem of an effect!
Diamond in the Rough by Ron Frost