Nugget of Knowledge: Pencil erasers

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Len Rome's Daily Feature of little known facts

(WYTV) – How does a pencil eraser work? It’s not like a chalkboard eraser that just wipes away chalk dust off a smooth surface.

Paper really isn’t that smooth, and a pencil mark isn’t all on the surface; most of it is embedded among the paper fibers.

Look at a pencil mark under a microscope. it’s not a continuous line. It’s made up of individual black particles, ten-thousandths of an inch long and they cling to the paper fibers and are also tangled among them.

The eraser’s job is to grab these tiny particles. The eraser is flexible so it can reach down among the fibers and it is just sticky enough to grab on to the black particles and pull them out.

But while it’s rubbing the paper, the paper’s fibers are rubbing off pieces of the eraser itself. So, you’re left with rubbed off shreds of rubber roll up with their black particles; the flecks you have to brush away.

Under the microscope, those flecks or crumbs look like enchiladas rolled in coal dust.

The black particles are graphite, a shiny, black mineral form of carbon that breaks apart easily into flakes. It’s mixed with clay and wax as a binder.

There is no lead in a lead pencil. Real lead is a soft, gray metal that will leave dark marks when we rub it on a smooth surface, and we did that until the mid 16th century when Swiss inventor Conrad Von Gesner made the first pencil.

Yet, more than four and a half centuries later we still call them lead pencils.

And rubber is called rubber because we use it to rub out pencil marks. In 1770, the English chemist Joseph Priestley was the first to use the term “rubber,” and it stuck.

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Mel Robbins Main Area Middle

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