Ever wondered how erasers actually work? The answer might surprise you

There's probably an eraser rattling around in your pencil case or in the junk drawer that you haven't given much thought to. It’s one of those things so ordinary it almost disappears until you actually need it. But what happens when the pink nub hits paper and a mistake disappears? The answer lies in the science of molecules, the science of heat, and a surprisingly rich history.

It begins with the way pencil marks work
Your pencil isn't actually made with lead. It never was. The core is made of graphite (a form of carbon) mixed with clay. As you drag it across paper, small layers of graphite flake off and stick to the page.

Why do they stick? Because of something they call van der Waals forces. Graphite consists of stacked two-dimensional sheets of carbon atoms, known as graphene layers, held together by these weak but real molecular attractions. According to a study published in the Journal of Chemical Physics, it is the van der Waals forces between the graphite layers that determine how the carbon sheets stick together and, more importantly, how easily they let go. As you drag your pencil across the paper, the layers of graphite are torn away and deposited on the paper, held in place by the same weak molecular attraction between the carbon particles and the paper fibers.


There is attraction, but it is not strong. That’s where the eraser comes in.

Why rubber beats paper
Rubbing an eraser over pencil marks is simple yet elegant. The graphite particles are more attracted to the eraser material than they are to the paper. The eraser is the winner of a molecular tug-of-war. The graphite lifts off the page and sticks to the rubber instead: those little grey crumbs you brush off your desk.

There is a mechanical side to this, too. The rubbing friction slightly abrades the surface of the paper and removes the settled graphite particles from the fibers. The softer the eraser, the kinder it is to delicate paper. The firmer the eraser, the more precise it is, but you can wear through the page if you press too hard.

The 18th century saw the introduction of natural rubber erasers, replacing such previous implements as balled-up stale bread and wax. Synthetic versions, usually polyvinyl chloride or other polymers, became more common in the 20th century, but the physics behind them is the same, no matter what the eraser is made of.

The pencil-eraser combo has a long history in the US
The eraser on the top of a pencil, so familiar that you hardly notice it, was first patented in Philadelphia in 1858 by Hymen Lipman. The idea took decades to become standard practice, but even then, pencil-and-eraser makers didn't always develop their products together. The combination we take for granted today was born of the slow convergence of two separate inventions.

What about erasable pens?
If you’ve ever used an erasable pen, a favorite of students and planners, you already know the weird thrill of seeing pen ink disappear, but it doesn’t act like a pencil eraser.

The ink in these pens is temperature-reactive, not friction-reactive. Peer-reviewed work published in the Journal of Chemical Education by Brent Znosko and colleagues found that the inks in erasable pens contain thermochromic compounds, which exist in a coloured form at low temperatures and a colorless form at high temperatures. As you slide the rubber tip of the pen over the page, the friction produces enough heat to induce the colorless state, and the writing seems to vanish. But it really hasn’t gone anywhere. The paper is still wet with ink. If you cool it off enough, the writing returns.

So erasable pens are great for planners and notebooks, but a bad choice for anything official. If you leave your journal in a hot car in July, your notes could simply disappear on their own.

Regular ink is a whole different story
Regular pen ink dries by absorbing into the paper fibers, becoming a part of the molecular structure of the page. This is why you can't just rub it off. There is nothing there on the surface to remove. Whiteners cover mistakes; they don’t erase them. It’s a workaround, not a solution.

The ancient Egyptians had the same problem, and they used white paint to cover up errors on papyrus manuscripts.

The eraser is still going strong
Sales of pencils and erasers are holding up, despite all the screen time and autocorrect in modern life. Every year, students, artists, architects, and office workers walk through them by the billions. That little pink rectangle hasn't been disturbed. And, once you know what it’s really doing, quietly winning a molecular race on the surface of your paper, it’s a little harder to take for granted.