How Do Erasers Erase?


(classical music) – I’m Cristen, and this is Brain Stuff. And there are plenty of
things I’d like to erase. The box of pizza rolls I ate yesterday, ever watching Sex in the City part two, and every single Willy Wonka meme. Just make them stop. 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 crystal and 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 pieces of 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 observations circa 1770 that this tree latex stuff
is great when you use to rub out pencil marks. Get it? Rub out? Rubber? Huh? But because natural latex
rubber can be expensive and some people are allergic to it, (coughs) condoms, 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
those paper fibers. And magic erasers work
on a similar principle. Magic. No, instead of being literally sticky, they contain rigid micro
structures 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. So hey, I want to know. What would you erase
if you had the chance? Tell me in the comments and if you like this video, make it official and
subscribe so you won’t miss the next one. And if you’re just pining
for more stuff from us, check out our site at brainstuffshow.com.

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