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  • It's estimated that for every 10,000 bills in the U.S.,

  • one of those bills is fake.

  • That may not sound like much,

  • but it adds up to millions of dollars in cold hard cash.

  • Counterfeit money has the potential to cause all sorts of problems,

  • from leaving you short $20 to destabilizing national economies.

  • But don't worry.

  • You can help catch the counterfeits.

  • All you need are some simple tools and a bit of chemistry.

  • First up, the anti-counterfeit detection pen.

  • The pen looks like a highlighter

  • and contains a solution of potassium iodide

  • and elemental iodine.

  • It reveals of the presence of starch,

  • which is commonly used to strengthen regular printer paper,

  • but won't be found in real money.

  • That's because authentic bills are made of cotton and linen

  • and are threaded with tiny red and blue fibers.

  • That material is made by a single, highly-guarded company

  • called Crane and Company,

  • which has been printing currency

  • since Paul Revere asked them to help finance the Revolutionary War.

  • The starch in many counterfeit bills, on the other hand,

  • is made of two molecules:

  • amylopectin and amylose.

  • It's amylose that gives the fake away.

  • Its long chain of sugar molecules connected by oxygen atoms

  • forms a helical structure, like DNA.

  • Iodide likes to squeeze inside this coil,

  • forming a new compound that leaves a dark mark on the paper.

  • However, in the absence of starch, there is no chemical reaction

  • and the mark will look light yellow.

  • So if the fake isn't printed on starchy paper,

  • iodine solutions can't help you.

  • That's one of the reasons U.S. bills printed since 1996

  • have been chemically enhanced to include another counterfeit countermeasure:

  • a strip that fluoresces under UV light.

  • That's the same kind of light used at black light parties

  • and airport security lines.

  • The polyester strip printed with invisble ink

  • is just one millimeter wide

  • and is found in different positions depending on a bill's value.

  • If you hold your dollar up to natural light,

  • you can see the amount and the word USA printed on the band.

  • But under UV light, these strips really shine.

  • They contain molecules that can be excited by absorbing certain amounts of energy,

  • specifically, that given off by common UV light sources.

  • As these excited molecules return to their original states,

  • they lose a bit of energy as heat and then radiate the rest as light.

  • Energy is inversely related to wavelength,

  • which means that the longer wavelengths have lower energy.

  • So the lower energy light given off by the strip

  • means longer wavelengths that fall in the visible range,

  • and suddenly we can see that which had been invisible.

  • And if a glowing strip doesn't show up on a recent bill,

  • you have a fake on your hands.

  • For times when you're not dealing with counterfeit masterminds,

  • looking for simple visual cues will do.

  • Make sure the portrait looks lifelike and not flat,

  • the seal has perfectly even sawtooth points,

  • the inked border is unbroken,

  • and the serial number has precisely equal spacing between each number.

  • So the next time you come across some dubious dough,

  • have a closer look,

  • pull out your iodine solution,

  • or take it to a rave

  • and you just might catch a counterfeit.

It's estimated that for every 10,000 bills in the U.S.,

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B2 TED-Ed counterfeit printed iodine uv light strip

【TED-Ed】How to spot a counterfeit bill - Tien Nguyen

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    稲葉白兎 posted on 2015/04/26
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