If you're doing a crossword puzzle, you probably want to use a pencil. That way, if you make a mistake, you can erase it.

If you use a pen with permanent ink, you'll likely be stuck with your answers — whether they're right or wrong!

Most people are familiar with liquid ink that can be found in pens. If you have experience with computer printers, you also know about liquid ink that comes in cartridges. There are even thick, pasty inks that professional printers use to print artwork and posters.

Basically, ink is a liquid or paste made up of pigments or dyes that is used to color a surface to create printed words or pictures. Modern inks are often made of complex combinations of various chemicals, including solvents, pigments, dyes, resins and other materials.

Ink has been around for centuries. No one knows for sure who invented ink. Experts believe that many different ancient cultures may have independently developed inks as they learned to write and draw.

For example, Chinese inks have been traced back to the 18th century B.C. The ancient Chinese who first made ink used plant, animal and mineral matter, mixed with water, to create different types of ink.

An ancient type of ink that's still used today for many different types of art projects is India ink. Used in ancient India since the 4th century B.C., India ink was called masi and was made of tar, pitch or burnt bones.

Today, India ink is made with fine soot called "lampblack," along with water and a binding agent, such as gelatin or shellac.

If you've ever gotten permanent ink on something it wasn't supposed to be on — like your shirt, for example — you may wonder why permanent ink is even made. Shouldn't we stick with pencil or ink that can be removed easily?

Not necessarily! There are plenty of good uses for permanent ink.

For example, there are many documents — such as legal documents — that we want to last forever. Think about the U.S. Constitution. You wouldn't want such an important document to be erasable, would you? Artists who use ink also usually want their art to stand the test of time.

Permanent ink lasts a long time, and that makes it ideal for important documents and works of art. Unlike pencil or erasable ink, permanent ink soaks into the paper it is used on.

The pigments and dyes in ink are usually dissolved in water and glycol. When these substances evaporate, the pigments and dyes soak into the paper, leaving a mark that will last a long time, if not forever.

Of course, permanent ink occasionally gets on things — clothes, skin, etc. — that you didn't intend for it to get on. When this happens, you sometimes can remove the permanent ink with special cleaners.

For example, permanent ink often can be removed with high-pressure cleaning, paint-thinning solvents or nail polish remover.

Even if these special chemicals don't remove the permanent ink completely, they often reduce its visibility. Over time, the permanent ink may fade away altogether.

And if you accidentally write on your teacher's whiteboard with a permanent marker? Don't worry! You can usually remove permanent marker from a whiteboard by drawing over it with a dry erase marker.

Why does this work? Dry erase markers contain acetone, a chemical often used as a paint thinner!

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