Pencil leads are the core material found inside pencils, primarily made of a mixture of graphite and clay. The graphite provides the ability to leave a mark on paper, while the clay helps to control the hardness and smoothness of the writing. The ratio of graphite to clay determines the pencil's hardness, which is graded on a scale from H (hard) to B (black), with F (fine point) in between. When you write with a pencil, the lead wears down and leaves a trail of graphite on the paper. This is why pencils can be sharpened to maintain a fine point. The pencil lead is encased in wood or a similar material, making it easy to hold and use for writing or drawing.