The Secret Science of Pencils
& Erasers

Cool Chemistry

What does the number on the pencil mean?

The pencil “lead” is actually a mixture of graphite and clay. More clay in the mixture makes the lead harder. A harder lead has a higher number. Pencils are numbered from 1-3 but most people use a number 2. Harder lead makes a lighter mark and softer lead makes a darker mark.

How long does a pencil last?

It’s been estimated that the average pencil has enough graphite to write about 45,000 words!

 

What if you made a mistake before they invented erasers?

Before using rubber for erasing, people used to use bread!