Curiosity Corner: Where’s the Lead?

Question: Why do we say “lead” pencil when it is not really lead? (Asked by Cruz Freimeyer, of Grantsville, W.Va.)

Reply: Don’t worry about getting lead poisoning from a lead pencil because it is not lead (Pb) but a nontoxic mixture of graphite (carbon, C) and clay. The lead connection comes from Roman times, when lead rods were used to write. Both lead and graphite leave marks on paper. Graphite didn’t come into use for writing until the 16th century, after very pure deposits of graphite were found in England. At the time, graphite was thought to be a type of lead and was called “black lead.”

In the 18th century, graphite was identified as a form of carbon. It was given the name graphite after the Greek “graphein,” meaning “to write.” Inks were widely used and applied with brushes called “peniculus,” Latin for “little tail,” and is where we get the word “pencil.”

The English graphite deposit was pure enough to be used directly, but expensive and not widely available. Lower quality graphite could be used, but needed something to keep it in usable form. It was discovered that mixing the graphite with clay and water produced a usable product once dried. This process is still used today.

Pencils are made by cutting slats of wood with a groove for the lead. A second slat is glued in a sandwich fashion and individual pencils are cut from the sandwich. These are processed with a recess cut for the ferrule (the metal ring that holds the eraser). This is then crimped into place.

Early pencils were unlabeled and unpainted, but that didn’t last long. In the mid-1800s, pencils made with high-quality Asian graphite were painted yellow to indicate the source of the graphite. The color caught on, and about 75% of the 2.8 billion pencils manufactured annually in the United States are painted yellow. Colored “lead” pencils are made from chalk and clay, and are mixed with binders and pigments. The pencil is usually painted the color of the lead for easy identification.

The hardness of the lead is indicated by a number (1-4). The higher the number, the harder the lead. There may be letter markings, such as “H” for hard, “B” for black, and “F” for fine (sharpened point). Also, there may be combinations, such as “HB” for hard and black and “HH” for very hard. I’ve graduated to mechanical pencils myself, but the lead hardness is still important.

Finally, a little pencil trivia. If laid end-to-end, the number of pencils made annually in the United States would circle the world 15 times. And although we are not in the form of graphite, the human body contains enough carbon to produce 9,000 “lead” pencils.

C.P.S. (Curious Postscript): “A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty.” -Winston Churchill

Curious about something? Send your questions to Dr. Jerry D. Wilson, College of Science and Mathematics, Lander University, Greenwood, SC, 29649, or email [email protected]. Selected questions will appear in the Curiosity Corner. For Curiosity Corner background, go to www.curiosity-corner.net.