Science Lab

An illustrated building with a microscope design above its double-doors. A water fountain sits in front of the stairs leading to the arched entrance.

Science is all about studying the world around us – from the animal kingdom to technology. To study these things, we must use our senses – like sight and touch.

Did you know that some creatures in the animal kingdom have things in common with U.S. currency? Both have some pretty cool special features. Here in the Science Lab, we'll find out what those special features are. You can discover them on your bills by feeling them, tilting them, and checking them with light.

Feel

The shell of the armadillo has a unique texture – it is rough to the touch with raised bumps.

A $20 bill with a section zoomed-in to show the raised texture over the shoulder of Andrew Jackson's portrait.

Raised Texture

U.S. currency also has a distinctive feel because of its special paper and the way that it's printed. If you move your fingers across the shoulders of the people on the bills, you will notice a raised texture that feels like bumps and ridges.

Did you know?

The human fingertip is the most sensitive part of the body. This is what allows you to feel these special bumps and ridges.

Tilt

An illustrated animation showing the shell of a jewel bug shifting between green and copper colors.

This is a jewel bug. But is it green or is it copper? It all depends on what angle you look at it.

An animated $10 bill tilting backwards.
The number 10 in copper at the bottom right of a $10 bill. The number 10 in green at the bottom right of a $10 bill. A directional arrow above the bill, showing the direction of tilt backwards and forwards.

Color-Changing Ink

U.S. currency can also look green or copper because of color-changing ink. To see the colors change, all you have to do is tilt it from side to side.

Color-changing ink can be seen on bills worth $10 or more. You can find the color-changing ink on the front of these bills, on the number in the lower-right corner.

The front of a $100 bill, flat. The front of a $100 bill, tilted backwards.
The number 100 in copper in the bottom right corner of a $100 bill. The number 100 in green in the bottom right corner of a $100 bill. A directional arrow above the bill, showing the direction of tilt backwards and forwards.
 
The front of a $100 bill, flat. The front of a $100 bill, tilted backwards.
A copper inkwell with copper bell within, on the bottom of the $100 bill. A copper inkwell with green bell within, on the bottom of the $100 bill. A directional arrow above the bill, showing the direction of tilt backwards and forwards.

On the $100 bill, there are actually two places where color-changing ink appears. It is both on the number in the lower-right corner and on the copper-colored inkwell. Inside the inkwell, you will see a bright green bell appear and disappear as you tilt the bill.

Did you know?

The human eye can see seven basic colors: red, orange, yellow, green, blue, indigo, and violet. This is also called the "The Color Spectrum."

An illustrated animation of a cuttlefish changing patterns on its skin.

Many animals have patterns on their skin. The cuttlefish can create any pattern it wants and can even make them move.

The front of a $100 bill, tilted forwards from the left. The front of a $100 bill, tilted forwards from the right.
The 3-D Ribbon down the middle of a $100 bill. The pattern on the 3-D Ribbon shifting on a $100 bill as the bill is tilted left to right. A directional arrow below the bill, showing the direction of tilt from side to side.
 
The front of a $100 bill, flat. The front of a $100 bill, tilted backwards.
The 3-D Ribbon down the middle of a $100 bill. The pattern on the 3-D Ribbon shifting on a $100 bill as the bill is tilted backwards. A directional arrow above the bill, showing the direction of tilt backwards and forwards.

3-D Ribbon

$100 bills have a special pattern on it's 3-D Ribbon. When you tilt it in different directions, the pattern will move and change. The images on the ribbon are bells and little "100's".

Check with Light

An illustrated animation of a jellyfish hiding a school of fish under its bell when the sunlight shines behind it.

Some jellyfish are actually hiding a secret. Take a look at this one against the light – you can see a school of fish hiding under its bell.

Close-ups of watermarks on the $20 and $5 bills.

Watermarks

U.S. currency also hides some secrets! All bills with a value over $5 have secret, hidden pictures on them that you can see if you hold a bill up to the light. These hidden pictures are called watermarks.

A watermark on a bill is usually the head of the person on the bill. But on the $5 bill, it is a number. These watermark numbers are on both sides of the bill.

A strip of special thread down the middle of a $50 bill.

Special Thread

When you also hold U.S. currency up to light, you'll also see a special thread hidden inside (in bills with a value of $5 or more). The thread is a narrow strip running up and down the bill. You can see it from both the front and back sides.

An illustrated animation of a millipede glowing brilliantly when UV light is shines on it.

This millipede looks normal until you hold it under an ultraviolet, or UV, light. Then it glows brilliantly.

$5, $10, $20, $50, and $100 bills under UV light showing brilliant strips of special thread.

Special Thread

When you also hold U.S. currency up to light, you'll also see a special thread hidden inside (in bills with a value of $5 or more). The thread is a narrow strip running up and down the bill. You can see it from both the front and back sides.

Watch: You'd Be Surprised Special Features

Now let's watch a video that brings to life all the cool creatures and features you just learned about.

Well, it looks like you're pretty much an expert on how paper currency is designed now. Be sure and take a look at all the things we have talked about every time you have a bill in your hand. If your friends are around, they would probably love to hear all about the artwork on it, how it can be spent and all the science each piece of currency contains.

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