(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
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