BrainStuff Classics: How Do Erasers Erase?

Erasers lift our mistakes right off the page, but it's not magic -- it's the microscopic physics of stickiness. Learn how erasers work in this episode of BrainStuff.

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Episode Transcript

Speaker 1 (00:02):
Welcome to brain Stuff from How Stuff Works. Hi, brain Stuff,
I'm Lauren voc Obam, and I've got something different for
you today. One of our classic episodes the topic how
do erasers a Race? This one was performed by our
previous host, Christian Sager and written by me, except for
the list in the beginning that was all Christian. I'll

(00:22):
let him take it away, everybody. I'm Christian Sager. This
is brain Stuff, and there are plenty of things I'd
like to erase. Maybe the sushi that gave me food
poisoning at one time, watching Battlefield Earth, and and pretty
much every tweet I ever read about Hamilton's and Mike Pence. Unfortunately,

(00:45):
a lot of marks in this world, however, are permanent.
But not so with pencil marks. Yes, the humble pencil,
or not so humble as the case. Maybe even in
this our digital age, about fifteen to twenty billion pencils
are manufactured each year. Each one holds the approximate capacity

(01:05):
to draw a line seven hundred and thirty two miles long,
or to write forty thousand words, all of which can
easily be erased. This blissful impermanence is thanks to the
materials that pencils and erasers are made from. See pencil
lead isn't actually lead at all, So no, you can't

(01:26):
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 seventeen nineties,
that graphite has been mixed with clay to achieve different
pencil lead hardness. Now, as you write or draw, flakes
of this clay and graphite mix cling to the fibers

(01:49):
that make up your piece of paper, and it is
a happening party for all particles involved. 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.

(02:11):
It's as simple as that. Since the flakes are just
hanging onto the paper, anything stickier than paper can lift
them off. In fact, the earliest erasers, going back to
at least the fifteen hundreds, were just bread slightly moistened
and baled up. Bread. Yeah, imagine what that tastes like
with pencil shavings in it. By the eighteen hundreds, people

(02:32):
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 Circus seventeen seventy that this
tree latex stuff is great when used to quote rub

(02:53):
out pencil marks. 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 it to make it more abrasive, which is

(03:14):
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. Meanwhile, erasable pens contain ink mixed with rubber cement.
While the cement is still wet, say within ten hours

(03:37):
of writing, it will stick to an eraser, and magic
erasers work on a similar principle. Magic. No, actually, it's
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. Yeah. Today's episode was produced

(04:05):
by Tyler Clang. As I said at the top of
the show, I originally wrote this script for our YouTube
video series for Kristen Conger to perform. If you'd like
to hear more from our former host, Christian, you can
check out his new podcast super Context wherever you listen
to podcasts, and of course, for lots more topics that
are always updating, visit our home planet, how stuff Works
dot com.