Hands-on history with Leonardo da Vinci

Have you ever thought about an invention that would make life a little easier - or even more fun? Have you ever wondered why something works the way it does, or dreamed about how to fly higher, swim faster, or travel farther?

A boy from Vinci, Italy, did just that more than 500 years ago. He dreamed big - and then went out to see if he could turn those dreams into reality. He is now known as Leonardo da Vinci (which means Leonardo from Vinci).

You might know him as a famous painter. He painted the "Mona Lisa" and "The Last Supper." They're two of the most famous works of Renaissance art. But Leonardo was more than an artist. "He was an incredible thinker, too," says Maxine Anderson, in a phone interview. She's the author of the children's book, "Amazing Leonardo da Vinci Inventions You Can Build Yourself" (Nomad Press; $14.95).

Ms. Anderson points out that Leonardo drew flying machines, armored tanks, and shoes that could walk on water. He thought anything was possible.

Most of what is known about him comes from the notes and drawings he jotted down in journals and notebooks. He filled more than a hundred of them with his mysterious "mirror writing." It's the kind of right-to-left handwriting that you hold up to a mirror to read.

People speculate about why Leonardo did this. "Some say it was to keep his ideas a secret," Ms. Anderson says. Others think it was because he was left-handed and writing right to left didn't smudge the ink.

You can try mirror writing on your own and send a secret message to a friend with our recipe for invisible ink on page 18.

In 2004, an Italian professor read through some of Leonardo's notebooks and discovered a "secret" recipe for a plasticlike substance that he may have used to make chess pieces, knife handles, and candleholders. Leonardo's idea came hundreds of years before real plastic was invented.

In addition to painting and inventing, Leonardo spent some time investigating optics. He wanted to know how the eye worked and why people saw things the way they did.

Using a camera obscura, a dark chamber with an opening that lets light inside, he found that the image projected from the outside world appears upside down.

"Leonardo realized that this is exactly how the human eye sees things," Anderson says. "Light reflects off the object you are viewing, and passes through a small opening on the surface of your eye. That opening, your pupil, flips it upside down."

What Leonardo never answered, however, was how, when we look at it, an image gets turned right side up again. That remained to be discovered many, many years later.

But the boy from Vinci continued to seek answers to his questions all his life. And his inventions, his discoveries, and, of course, his paintings continue to amaze and inspire people today.

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When Leonardo da Vinci lived, in the 15th and 16th centuries, there weren't digital cameras - or cameras at all, for that matter. If you wanted to capture an image, you had to paint or trace it. That led Leonardo to experiment with a "dark box" known as a camera obscura. It allowed just a tiny ray of light to pass into a darkened box, making images from the outside appear upside down on the opposite end. This was the predecessor to modern cameras.

Pringles canister with lid
Sharp scissors
Tape
Aluminum foil
Pushpin

Cut through the canister about 2 inches from its base. Place the lid on the shorter piece of the canister. Then put the taller portion of the can on top of the lid, securing it with tape.

Poke a small hole in the bottom of the canister. Wrap the sides of the can in aluminum foil to block out light.

Go outside and hold your camera obscura with the pinhole end to your eye. Cup your hands around the end you're looking through in order to block out any extra light from entering the canister. You should be able to see an upside-down image reflected on the inside lid of your camera obscura.

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Leonardo enjoyed playing practical jokes on friends. Once he licked the end of a stick and used it to write a message that appeared as black ink. How did he do it? Some think the paper had a special solution on it, similar to this recipe for invisible ink.

Small glass of lemon juice or milk
Q-tip
Piece of white paper
Blow-dryer or light bulb

Dip the end of the Q-tip into the lemon juice or milk, and use it to write a secret message on the piece of paper.

Let dry completely. Your message should be invisible.

To decode your message, heat the piece of paper by carefully blow-drying it (or holding it near a warm light bulb).

As the paper heats up, your message will appear yellow or brown. That's because milk and lemon juice are acidic and weaken the paper, Anderson says in her book. "When the heat source is put near the paper, the weaker part begins to brown before the rest of the paper does."

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He didn't invent plastic, but Leonardo may have applied a plasticlike substance to his paintings to act as a laminate for the paint. He also may have used this "natural plastic" for other useful tools such as knife handles or candleholders. Here's how to make your own version of Leonardo's plastic.

1/2 cup heavy cream
4 tablespoons white vinegar

Have an adult help you with this. Pour the cream into a saucepan and stir over medium heat. Do not let boil. When the cream starts to simmer, stir in two tablespoons of vinegar. You will start to see yellowish lumps (curds) forming. Add the rest of the vinegar and continue to stir until the liquid turns mostly to curds.

Take the saucepan off the heat. Pour the curds into a strainer. Rinse with cool water. Knead curds together into a ball. Then shape it and let dry overnight.