This trick can be repeated over and over again without any fear of detection.
Using any pack, openly remove five red and five black cards, (It is best to keep to spot cards though not essential.) then discard the rest of the pack.
Put the two stacks of cards face to face - that is, all cards of one colour together face up and all of the other colour face down on top of them. Thoroughly mix the cards, using an overhand shuffle being careful that none of the cards turn over while you shuffle them.
Place them behind your back and count off the top five, turning this stack of five over. Bring both stacks round to the front again. Spread them in two separate strips along the table and there will be an equal number of face-up cards in each pile. But they will all be alike in colour in each pile.
Let's see that again! Reverse one of the stacks and place the two piles together again, shuffle and put them behind your back as before and repeat. You can keep on doing this all day and the effect will be the same.