WEBVTT

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

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one of those bills is fake.

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That may not sound like much,

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

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

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from leaving you short $20
to destabilizing national economies.

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But don't worry.

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You can help catch the counterfeits.

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

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First up, the anti-counterfeit 
detection pen.

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The pen looks like a highlighter

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and contains a solution 
of potassium iodide

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and elemental iodine.

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It reveals of the presence of starch,

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which is commonly used 
to strengthen regular printer paper,

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but won't be found in real money.

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

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and are threaded with tiny 
red and blue fibers.

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

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called Crane and Company,

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which has been printing currency

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

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

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is made of two molecules:

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amylopectin and amylose.

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It's amylose that gives the fake away.

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Its long chain of sugar molecules
connected by oxygen atoms

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forms a helical structure, like DNA.

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Iodide likes to squeeze inside this coil,

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

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

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and the mark will look light yellow.

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

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iodine solutions can't help you.

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

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have been chemically enhanced to include
another counterfeit countermeasure:

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a strip that fluoresces under UV light.

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

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and airport security lines.

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The polyester strip 
printed with invisble ink

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is just one millimeter wide

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

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If you hold your dollar 
up to natural light,

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

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But under UV light, 
these strips really shine.

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

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specifically, that given off 
by common UV light sources.

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As these excited molecules return
to their original states,

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

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Energy is inversely related to wavelength,

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which means that the longer wavelengths
have lower energy.

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So the lower energy light 
given off by the strip

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means longer wavelengths
that fall in the visible range,

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and suddenly we can see that 
which had been invisible.

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

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you have a fake on your hands.

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

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looking for simple visual cues will do.

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Make sure the portrait 
looks lifelike and not flat,

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the seal has perfectly 
even sawtooth points,

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the inked border is unbroken,

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

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So the next time you come across 
some dubious dough,

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have a closer look,

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pull out your iodine solution,

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or take it to a rave

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and you just might catch a counterfeit.