Erasers have come a long way
since the early days of using moist
bread to eradicate errors.

You probably don't think about pencils
and erasers much in today's world of
digital and mobile access to everything;
while it's undeniable that the No. 2
pencil and the SAT have a long history
together, pencils don't really come up
much outside of standardized testing
anymore. But despite our devotion to
our devices, Americans still use more
than 2 billion pencils every year
.
Contrary to popular belief, pencils
aren't really made with lead, and
haven't been since Roman scribes
wrote on papyrus -- that's a common
pencil myth. So if you chew on your
pencils, rest assured you won't become
ill from lead poisoning (although that's
not a free pass to snack on a No. 2).
Today's pencils are made with graphite,
water and clay (which is used as a
binder), and pencil lead has been made
this way since Nicolas-Jacques Conté
invented the mixture in 1795. They weren't topped with an
eraser tip, though, until about a century
later. And it's this companion to the
pencil, the eraser, that we're interested
in here.
Erasers eradicate pencil markings by
lifting graphite from the paper you've
written on. As you write, particles of
graphite from your pencil mingle with
and cling to particles in the fiber of the
paper. Here's the science: Modern
erasers are almost always made from
petroleum-based synthetic rubber
compounds, typically polyvinyl chloride
(they're no longer made from natural
latex rubber, which is an allergen for
some people). Because the particles in
the polymer that make up an eraser are
stickier than paper, those graphite
particles get stuck to the eraser
instead. Some erasers are stickier than
others and absorb graphite particles
more easily, giving you a cleaner, less-
abrasive result.
Believe it or not, one of the very first
erasers used was moist bread.

SOURCE: electronics.howstuffworks.com/everyday-tech/erasers-erase.htm