Pencil Day

What the day is

Pencil Day is observed on March 30, the anniversary of an 1858 patent granted to Hymen Lipman for a pencil with an eraser fixed in one end.

Origin and background

The patent has an instructive ending. It was sold on for a large sum, and when the new owner sued a rival, the Supreme Court invalidated it in 1875, reasoning that attaching two known things did not make an invention, because the pencil still wrote as a pencil and the rubber still erased as rubber, neither doing anything new in combination. It remains a standard illustration in patent law of the line between a combination and an aggregation.

The material is the other misunderstanding. There is no lead in a pencil and never has been. The core is graphite, a form of carbon, and the name is a translation error dating to the discovery of a large deposit in northern England in the sixteenth century, where the soft black mineral was taken for an ore of lead.

Graphite alone is too soft and too crumbly to write well, so modern cores are graphite powder mixed with clay, fired, and impregnated with wax. The proportion of clay is what the grading scale measures: more clay makes a harder, lighter core, more graphite makes a softer, darker one. An H pencil is not made of different material from a B, merely a different ratio.

Even the shape is deliberate. Hexagonal pencils are cut from slats with almost no waste, they are cheaper to make than round ones, and they do not roll off a sloping desk, which is why carpenters' pencils are flatter still.

A pencil line is not chemically bonded to the paper but sits as flakes caught in its fibers, which is why an eraser works by lifting rather than dissolving.

How to take part

• Try a softer grade than you normally use. Most people write with too hard a pencil.
• Sharpen with a blade rather than a sharpener for a longer, more controllable point.
• Read the 1875 ruling, which is short and surprisingly readable.
• Notice that nothing you own called lead contains any.