How Do Erasers Take Away Writing?

Pencils make marks with bits of lead left on the paper. But those bits stick to the eraser and come off with it. The marks a pencil makes are powdered bits of its lead that are ground off by the pressure of writing and stick lightly to the paper. The eraser is soft enough that its surface is sticky. Rubbing it across the marks both picks up the lead powder and scrapes off the bits of the eraser to which they stick. The eraser is self-cleaning. Most erasers today are made of synthetics. An ink eraser contains very fine sand. It has to rub off the ink-soaked surface of the paper itself. Crayons use coloured wax to make marks, and it sticks to the paper. So erasers cannot rub it off.