The Stained Glass Effect by Simon Caine

A deck is borrowed from a spectator. The deck is shuffled by the spectator. They select a card and commit it to memory. Nothing is forced, no card is mentioned out loud.
A second spectator is thinking of any number between 1 and 52, the card is replaced and the deck is further mixed. Nothing is forced, no number is mentioned out loud.

Only after both spectators are satisfied with the random state of the deck are the freely chosen card and number named out loud (only if they want! This information can stay unknown to the performer the whole time.)

The performer does not touch the deck, and invites the second spectator to count down through the deck to the number she is thinking of. The first spectator turns over the card at that number to reveal the card she is thinking of. This is The Stained Glass Effect.

Spectator Shuffled Deck
Deck can be Borrowed or Incomplete
Impromptu
Almost Entirely Hands Off
No Stacks, Gimmicks, Memorisation, Forces, Peeks or Indexes
Self Working
[Note: This effect requires you to crimp one card in advance (in case it is your deck) or during a prior effect or on the off-beat (in case it is a borrowed deck). You will also need to be able to cut to the crimped card.]