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How Do Erasers Erase?


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Channel: BrainStuff - HowStuffWorks
Categories: Chemistry   |   Science  
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Erasers lift our mistakes right off the page, but it's not magic - it's the microscopic physics of stickiness.

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I’m Cristen, this is BrainStuff, and there are plenty of things I’d like to erase: The box of pizza rolls I ate yesterday; ever watching “Sex & the City Part 2”; and every single Willy Wonka meme. Unfortunately, a lot of marks in this world are permanent. But not so with pencil marks.

Yes, the humble pencil – or not-so-humble, as the case may be.

Pencil lead isn’t actually lead at all. (So no, you can’t get lead poisoning from a pencil wound.) It’s made from graphite, which is a soft mineral made up of flaky, atom-thin layers of crystalline carbon. Ever since the 1790s, that graphite has been mixed with clay to achieve different pencil lead hardnesses.

As you write or draw, flakes of this clay-and-graphite mix cling to the fibers that make up your piece of paper. The fibers have a huge surface area that catches lots of flakes, and the flakes will gladly stick around for decades if they’re not disturbed.

But erasers can lift those flakes right off the page by virtue of being stickier than the paper fibers. It’s as simple as that. Since the flakes are just hanging onto the paper (not unlike thousands of tiny clay-and-graphite kittens, just hangin’ in there), anything stickier than paper can lift them off.

In fact, the earliest erasers, going back to at least the 1500s, were just bread. Slightly moistened and balled up bread.

By the 1800s, people were using erasers made from natural rubber, which is harvested in the form of latex from certain trees, which excrete it to discourage plant-eating insects. (The name “rubber” actually comes from one chemist’s observation, circa 1770, that this tree latex stuff is great when used to “rub out” pencil marks. Rub-er.)

But because natural latex rubber can be expensive and some people are allergic to it, modern erasers are almost always made from synthetic, petroleum-based rubber like polyvinyl chloride.

Your standard pink eraser has bits of pumice added to make it more abrasive, which is a cheap way to help dislodge flakes of graphite from paper fibers. Fancier erasers are made from super-sticky soft vinyl that absorbs the graphite and is more gentle on your paper.

And magic erasers work on a similar principle: Instead of being literally sticky, they contain rigid microstructures that trap dirt. But if you’re ever without one, give your standard pink eraser a try – they’re effective on way more than just pencil marks.


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