How Do Erasers Erase?

Erasers lift our mistakes right off the page, but it's not magic - it's the microscopic physics of stickiness.

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Episode Transcript

Speaker 1 (00:02):
Welcome to brain stuff. From how stuff works, everybody, I'm
Christian Seger. 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

(00:22):
Hamilton's and Mike Pence. Unfortunately, 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 are digital age. About fifteen to
twenty billion pencils are manufactured each year. Each one holds

(00:44):
the approximate capacity to draw a line seven hundred and
thirty two miles long, or to write forty words, all
of which can easily be erased. This blissful impermanence is
thanks to the materials that councils and erasers are made from.
See pencil lead isn't actually lead at all, So no,

(01:05):
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 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

(01:28):
to the fibers 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

(01:49):
than the paper fibers. 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
array's 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

(02:10):
the eighteen hundreds, 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 Circus seventeen seventy
that this tree latex stuff is great when used to

(02:32):
quote rub 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,

(02:53):
which is a cheap way to help dislodge flakes of
graphite from paper fibers. Fan to your 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,

(03:15):
say within ten hours 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. Check

(03:44):
out the brain stuff channel on YouTube and for more
on this and thousands of other topics. Visit how stuff
works dot com,