What Materials Can Magicians Use to Secretly Mark Playing Cards for Detection?

[DrinkGreenTea]

I'm a magician. I want to implant unnoticed gimmicks of different weights or charges, or some other different amount of property which can be detected easily into each playing card of a deck of cards. What physical material can I use to implant into them where some type of reader on my wrist can detect when a traceable amount is pulled away. So I can see the change in amount of the detection and correlate which card was pulled away. Looking at the reader of a change of X amount, I would know exactly which card was pulled out of the deck.
Would this be possible by creating magnetic field changes which can be read. Does anyone have some practical and/or plausible ideas to help me work on this? Thank you.

 

[Danger]

Welcome to PF, DGT.
I hate to say this, but you are barking up the wrong bush.
One of my hobbies is designing illusions, and the one that you want is worth at least $5,000 for an exclusive deal.

 

[DrinkGreenTea]

How is this barking up the wrong bush? I think there are intelligent minds here who can figure something out, even something better than before for this illusion. There must be a very easy and practical solution to this. I would like to hear some more input on this question and it is obvious that physics has the answer. I am not talking about microscopic radiotransmitters or anything expensive like that either. Something along the lines of slivers of magnets at different weights in which a field detector can measure a small change when one of the slivers in removed. Basically anything that is small, causes an effect when grouped with others which can be measured, and when one is taken away, the measured effect would be changed and you can figure out how much of X was taken away. And also something that can be easily measured with a reasonable device.
I feel that this is a very reasonable physics question.

 

[Delta2]

Well it seems to me that this post is suited more for electric engineering forums but i think the field detector has to be very accurate and very small so even if you can make/find one it would be very expensive.

 

[Danger]

I'm sorry if you misunderstood my point; it was poorly expressed. The simple fact is that we help people with personal projects at no expense. What you are asking for, though, is something that you will profit from. That sort of information isn't just given away. It would be roughly equivalent to me designing a next-generation skateboard for you and having you take out a patent on it. We do the work, and you get paid for it.
I really hope that you don't consider me unfriendly because of this stance. I love working on stuff like this, but the fact is that I'm living on a disability pension that barely pays for my groceries. If any of the people that I've built things for in the past 35 years had offered me even 5% of their resultant profits, I'd be a millionaire several times over.
That having been said, I've been up for over 40 hours and have been drinking the whole time, so I'm not at my best right now. Perhaps I will be more amenable to helping you when I've had some sleep and sobered up.

 

[DrinkGreenTea]

I'm not asking for anyone to design anything. I'd just like to see the physicist's point of view of the most plausible and practical material to use. Is magnets with a field detector the way to go, or weights with a small digital sensitive scale, or different resistors which a current can run thru, etc. I'm not trying to gain profit from this either, I only do magic for free as a hobby.

 

[Danger]

Oh... :shy:
Apparently, the misunderstanding was on my part. I apologize.
The "nap" idea didn't quite work out, so I'm even more tired and drunk than I was the last time that I posted, but I'll give it a shot. Bear in mind that my first couple of dozen thoughts are not usually the good ones. My approach is to free-wheel and see what sticks to the wall.
My first idea is to print your own deck, using either magnetic ink or embedded RF tags. If you are in a totally controlled environment, though, you could also investigate using optical sensors to track the cards.
That's all that I have for now. Again, I'm sorry that I snapped at you.

edit: Oh, crap! This is worse than I thought. I just turned on the TV because my evening shows should be starting, and discovered that it's 7 am, not the pm that I expected. Perhaps I should either switch to a different brand of beer or quit drinking after the first couple of dozen.

 

[DrinkGreenTea]

I don't know if magnetic fields are practical, affordable, or if there is a small enough sensitve reader, does anyone have any info on this?
Here is my idea on using weight:
Is there a super sensitive digital scale that can be placed inside the card box? The participant takes a card, you put the rest of the deck in and maybe there is a small cut on the bottom of the card box to see the display of the weight. Do such small and sensitive scales of this sort exist? And what material would be practical weights to use which can be inserted onto cards unnoticed?

 

[Robot B9]

What would be very clever would be to print the cards with conductive ink in a pattern that would allow the cards to act like RFID tags...

Then a RFID reader on a wrist band could "somehow" signal you what card is what.

 

[Cleonis]

[...]
So I can see the change in amount of the detection and correlate which card was pulled away. Looking at the reader of a change of X amount, I would know exactly which card was pulled out of the deck.
Would this be possible by creating magnetic field changes which can be read. Does anyone have some practical and/or plausible ideas to help me work on this?

I have to say, I'm quite pessimistic about this endeavour.

I don't see a scheme where cards are magnetized in some way, allowing you to identify the single card that is missing from a deck. As to using weight: no doubt sufficiently sensitive, sufficiently small weighing devices exist.
The hard part would be to manipulate the individual cards of a deck in such a way that you can differentiate between them. Assuming quite sturdy cards I estimate a weight of 2 gram per card. Assuming the weight difference between the cards must be 10% max you can vary the weight from 2000 to 2200 microgram.
That would lead to a scheme with successively the following weights: 2000, 2004, 2008, 2012, [...] , 2204, 2208

You calibrate the weighing scale to counting units of 4 micrograms, so you count as if the cards of the deck are 501, 502, 503, 504, [...] 551, 552 units

Total weight of the deck in such units: 26000 + 1378 = 27378

If you can manage to manipulate the weight of individual cards to within microgram precision you have a shot at the above scheme. As said, the hard part would be to manipulate the weight of the cards that precisely, while preserving the look of an untampered deck.

The reason the weight scheme can work in the first place is that weight is straightforwardly additive. The order of the deck does not matter, weight just adds up.

By contrast, magnetism has magnitude and direction, and a magnetic field falls of with the third power of distance. When sensing a magnetized object the orientation of the sensor relative to the magnetic field matters. Distance matters a lot, so for the accumulated magnetic field the order in a deck of cards would matter. There are just way, way too many variables to have any chance of a reproducible reading.

 

[Dr Lots-o'watts]

This reminds of credit cards with chips. I think you want to implant chips in a deck of cards.

 

[yinx]

Whatever you are trying to build might be a little too complicated, and impractical for performing for live audience.

I would suggest that you head down to your local magic supply store and get yourself a marked deck, probably around 10 dollars.

If you want to save some money, you can make yourself a marked deck using ordinary bicycle decks.

 

[JaredJames]

Would it not be easier to use some sort of 'invisible' marker and wear a pair of glasses that allow you to see it (if that system exists)?

I actually have a set of marked cards. They have extremely subtle changes in the designs on the rear of the cars which you wouldn't notice if you didn't know they were there.

 

[DrinkGreenTea]

I don't want to use any marked decks. I want this to be extremely examinable that it can even fool magicians. The glasses idea might be too suspicious.

 

[JaredJames]

Well if the greatest magicians haven't come up with the type of system you're talking about, there's probably a good reason for it.

 

[Jack21222]

There are countless ways to force them to pick the card you want them to. Why leave it up to chance what card they pick?

 

[DrinkGreenTea]

With that attitude no new inventions will ever be made and we would be stuck without progress.
Because having them pick a card honestly by choice will blow people's minds.

 

[Jack21222]

With that attitude no new inventions will ever be made and we would be stuck without progress.
Because having them pick a card honestly by choice will blow people's minds.

If you do it right, they think they picked the card honestly.

 

[WarVsFutility]

This reminds of credit cards with chips. I think you want to implant chips in a deck of cards.

Yeah. You could have a watch or some radio device which detects which card you aren't in physical contact with anymore, and somehow communicate with you in an inconspicuous manner, like little shocks, or something. Each card could have its own IP address... then when it is taken out of the deck, you would know which one!

Very little shocks, of course:)

 

[JaredJames]

Chips in the cards would add a noticeable imbalance to them plus they aren't exactly slimline in comparison to playing cards.

I've been trying to think about this for a while and just can't see a way of doing it. To get a 'good' reading, you'd have to be in close contact to the card they choose and no other (to avoid mis-readings).

The only thing I could come up with would be taking a piece of copper wire (exceptionally small diameter) and cutting it to different lengths. Somehow building the various lengths into the cards and then inducing a current and measuring the resultant magnetic field (you'd have to arrange the wire correctly to get different results). It would have to be sooooo sensitive it just isn't feasible.

Or

You could magnetise different pieces of steel (again in microscopic quantities) and then simply check the strength of the field as they hand you the card. Again though, it would have to be amazingly sensitive to work and as such is unfeasible. (That and they'd probably have an effect on each other.)

 

[swahelian]

I don't know how easy this would be to make and if it would work well, but:
How about making a custom deck where each card has unique electric resistance. The cards have to make a physical connection when stacked though so that you can somehow attach an ohmmeter to it.

 

[Danger]

I don't know how easy this would be to make and if it would work well, but:
How about making a custom deck where each card has unique electric resistance. The cards have to make a physical connection when stacked though so that you can somehow attach an ohmmeter to it.

That is as practical as anything else mentioned.
My first instinct, though, is to use optical sensors in an alternate-light-source frequency such as UV to read a marked deck.
Jack, I agree that "forcing" a card is an artform like no other. I know how it's done, and have still have had it done to me by an expert. Embarrassing, but educational.

 

[sophiecentaur]

Do you just want to count the number of cards in the deck or identify which ones have been taken out?
It might be possible to fit each card with its own resonant circuit (a bit like the security stickers in library books) which could respond to a particular Radio Frequency signal. A scanner with 52 frequency steps could detect which cards were there and which were missing. The cards might need to be a bit fatter than normal - or very expensive. You could be coded with invisible bands of 'colour' - say infra red dyes - which a detector could detect and decode the value of the chosen card. That would be, effectively, a marking system, only visible to your gizmo and some insects.
If you wanted to compromise your health, you could have a small square of metal foil between the front and back of each card and use a weak X ray source. With all cards in the deck, there would be no x rays emerging but one missing card would leave a hole in a specific place, corresponding to one particular card. This would work whether or not the pack had been shuffled. A suitable arrangement would work even if the cards were rotated or turned over. But there would be the X ray problem . . . . you'd need the source in your 'wristwatch' and the detector / imaging system under the table top. I guess you could do it optically, with the appropriate material for the cards: opaque to visible light but transparent to UV or IR. Reminds me a bit of the old computer card reading systems.

 

[Danger]

Sophie, that is one of the most off-the-wall approaches to anything that I've ever seen. I love the way that your mind works.