Solution To Vickis Tricky Question

[See VickiKerr page.]

If Vicki tries to delete this page, we'll know there is no "secret". Hah!

Of course there is, but it's easier to guess if you actually do some shuffling to see what happens a) with a standard deck, b) with a deck which is even very slightly non-standard. Consider what effects can accumulate despite the tendency of the shuffling to randomize the order of the cards. Also consider what scope the performer has to influence the order of the cards without handling them (after all, the performer is giving the shuffling instructions).

One person has now guessed correctly.

Don't scroll down if you don't want to learn the secret. -- vk

I'm unaware of any ways to influence the order of cards without handling them. Probably just a personal problem. And while all magic tricks are disappointing when you know how to do them, I am expecting this one to be really disappointing. --rj

No fair. This is the page for the solution, not for more tricky Vicki hints :-) -- ad

Remember, unsigned comments are still liable to get deleted, even here! -- vk

Anonynous witticism deleted.

There was a significant hint to try two standard linen-based decks. Combine red from one and black from the other. Perhaps the directionalities of the grains are important as well. I would try this, but I don't own a deck of cards and don't plan to anytime soon. -- ss.

It's not grain differences that count. The cards need to be of reasonably good quality. Cheap cards get damaged too easily (especially during a riffle shuffle) and often aren't even all the same size. Some plastic-coated cards are well made, but they tend to be so shiny that the shuffling works 'too well'. The 'linen-finish' is not, as far as I know, actual linen, but a matt finish often used for cards of good quality. Also, matt finish cards give the performer a better view, which is rather handy! -- vk

I guess the secret is that Viki owns stock in several card manufacturing companies. If everyone who reads Wiki goes out and buys two decks of "good quality" cards and shuffles them to death trying to guess the secret...well, you see what I mean. -- wm

It's not grain differences that count ... Some plastic-coated cards are well made, but they tend to be so shiny that the shuffling works 'too well'.

If you read on, please do not disclose the method to others. -- vk

OK, I've solved it.

Buy two linen-backed packs of cards. Flex each pack a little; just enough for the cards to hold a slight curvature after flexing, but not enough to be noticeable by the average shuffler. Flex the packs in different directions.

Combine the red cards from one pack with the black from the other pack.

When the card-player shuffles (with an overhand shuffle), there will be a tendency for cards with the same curvature to stay together and indeed to accumulate. Adjacent cards with the same curvature will have a much higher friction than adjacent cards with opposing curvatures - so the overhand shuffle will tend to group cards with matching curvatures.

The performer must of course stop the process at an appropriate time. That's the "performer effect" and it's not difficult. Try giving someone a pack of cards to "shuffle thoroughly" - an almost subliminally-quiet "ok" will cause them to stop shuffling without them realizing that they have been manipulated.

Clearly, the performer needs a good view of the cards - but it's not necessary to see individual cards, just the "texture blocks" made by groups of adjacent cards with the same curvature.

The performer also has an additional chance to improve the sorting of the cards by requesting (or not requesting) them to be cut and reassembled after the shuffling.

Obviously the trick is not 100% repeatable - but a skilled performer should be able to obtain a pretty good red-black separation most of the time.

Thanks Vicki for this one - it has kept us enthralled for many months. The interest, of course, came from the process of prising clues out of you rather than from the card trick itself. -- RogerBrowne

Brilliant - well done. Completely correct bar some minor details. One doesn't need to use two decks. If the red cards are handled more, their edges will be slightly duller, making blocks distinguishable. Seeing such blocks is useful, but not essential. The shuffling needn't be stopped immediately, as an overhand shuffle of a red-black separated deck often makes no difference to the separation, merely exchanging red and black. If the performer notices red (or black) blocks at the top and bottom of the deck, a cut will bring the blocks together. Surprisingly few shuffles are needed, and only a really tiny amount of curvature is required. Triple-flexing, giving the cards an almost imperceptible waved profile avoids loss of the curvature due to handling. The weight of the cards is sufficient to ensure the cards appear completely normal when placed face-down in a neat stack. Identical cards are held together by air pressure as well as friction. Other methods relying purely on friction affect the handling qualities of the cards too much. Rough handling of the cards is avoided by suitable instructions and the use of a card-player. -- VickiKerr

The interest was supposed to lie in the reasoning processes applied by readers rather than the quality of the trick or the techniques for obtaining hints! -- vk

You will have to have an alternative if the player shuffles too well or does not stop at the right moment. Did someone actually perform this trick? Yes. If the card-player (who agreed to participate) sets out to spoil things, some more helpful card-player can be asked to shuffle the cards as well.

Note that the cards should be symmetrical, and the player should not use his/her thumb to draw off cards during overhand shuffling, but instead release cards by slightly opening the grip of the holding hand. -- vk

I have a better solution, I think, correct me if I'm wrong.

A deck of cards in which all red cards are very slightly non orthogonal in this way: "\_/", with the bottom edge very slightly thinner than the top. All the black cards, on the other hand (except for one which is shaped like a red card) have their top-edge very slightly thinner than the bottom edge. It is better if the cards are laminated and smooth.

The deck is opened on stage, already shuffled (so the player won't notice the uneven surface). The player is instructed to shuffle thoroughly, but manipulated (by demonstration) to use a shuffling that doesn't rotate the cards (so the top of both red and black cards always face front).

Now to separate the cards all the performer has to do is hold the deck in it's center with both hands and slide the cards to the bottom and the top. The red cards (and one black) will slide upwards and the blacks will go with the bottom slide.

As long as the cards haven't been rotated during the shuffle (most shuffles do not rotate) this will always work... - TalRotbart

You can buy trick packs with this non-othogonality. I used to have one when I was a kid. -- PaulHudson

Such packs are often made poorly - a) by excessive non-orthogonality, and b) by being made by cutting down a standard pack along a straight line, thus spoiling the corners. Since such packs are quite well-known, I find that many people check for such trickery if they have any reason to suspect the pack. Also, the separation move described is a sleight (one which could be noticed), and requires performer handling to do it. -- VickiKerr

Part of the difficulty of this trick is that the performer does not handle the cards at all. See the original discussion on Vicki's page.