Most adults probably realize
that there isn't any elemental lead in a pencil. The connection
between graphite and lead stems from the days of the Roman
Empire (and likely before that), when lead rods were used
by scribes to write on papyrus. Both graphite and lead
leave a gray mark on paper, although graphite is a bit
darker. Graphite didn't
come into widespread use for writing until after the 1564
discovery of a very pure graphite deposit in Borrowdale,
England. At the time, graphite was thought to be a type
of lead and consequently was
called black lead or plumbago.
In 1779, Swedish chemist Carl W. Scheele determined that
black lead was actually a form of carbon; in 1789, German
geologist Abraham G.
Werner reportedly gave it the name graphite, after the
Greek graphein, meaning "to write." Inks were
already widely available and were usually applied to paper
with a brush called a peniculus, which is Latin for "little
tail," hence the basis for the word "pencil."
Charcoal probably was used in ancient times to mark on
paper as well.
Graphite from Borrowdale originally was used in chunks
called marking stones. Because graphite is softer and
more brittle than lead, it requires a holder when carved
into pencil-shaped sticks for
writing. At first, sticks of Borrowdale graphite were
wrapped with string, and the string was slowly unwound
as needed as the writing core wore down. Later on, graphite
was inserted between two slats
tied together or into wooden sticks that were hollowed
out by hand to create the first wood-cased pencils.
The Borrowdale deposit was pure enough to use without
modification. But lower quality graphite needs help to
keep it in a usable form. Various binders mixed with graphite
powder have been tried, such as gum, resin, or glue. Sulfur
also has been mixed with graphite, which results in writing
cores most like pure graphite. In 1795, French
chemist and Napoléon courtier Nicolas-Jacques Cont?invented
a process to mix graphite with clay and water, a process
that is still used.
TODAY, GRAPHITE AND clay are crushed into a fine powder
in a rotating drum containing large rocks. Water is added
and the mixture is blended for up to three days. The water
is pressed out of the mixture, leaving a gray sludge that
is air-dried until it hardens.The dried sludge is ground
into a powder, water is added again, and the mixture is
blended to form a soft paste. Carbon black may be added
to increase the dark-ness of the lead. The paste is extruded
through a metal tube to form thin rods that are cut into
pencil-length pieces--called leads--that are then dried.
The leads are heated in an oven to 1,800 &°F (about
1,000 °C) or higher to make them smooth and hard.
The ratio of graphite to clay can be adjusted to vary
the hardness of the lead: the more clay, the harder the
lead; the harder the lead, the less graphite comes off
onto the paper, making a lighter line.
Pencils are made by cutting blocks of wood into slats
that are machined to form a groove (two to nine per slat)
to place the leads.
A second slat is glued onto the first, sandwich fashion,
then individual pencils are cut from the sandwich and
sanded smooth. The pencils are next painted with five
to eight coats of paint, and a
recess is cut for the ferrule--the metal ring that holds
the eraser. The ferrule and eraser are crimped into place,
and a metal stamp is used to press a label onto the pencil.
Various types of wood have been used to make pencils over
the years. Red cedar from Kenya and the U.S. was an early
favorite, but today nearly all pencils worldwide are made
from incense cedar, a species that grows in California's
Sierra Nevada Mountains. The first pencils were unlabeled
and unpainted to show the fine grain of the wood used.
But by the 1890s, manufacturers started stamping their
names on pencils and painting them.
THE LATTER TRADITION
got started when a French merchant-adventurer named
Jean-Pierre Alibert discovered very pure graphite along
the
Russian-Chinese border in the mid-1800s. Alibert later
developed a mine and began shipping the graphite to
points around the world. Pencils made with high-quality
Asian graphite were painted yellow to indicate the source
of the graphite. Although there are several domestic
and international sources of graphite today, about 75%
of the 2.8 billion pencils manufactured annually in
the U.S. are still
painted yellow.
The hardness of the lead is indicated by a number (1
to 4) stamped on the side of most pencils--the higher
the number, the harder the lead. Sometimes there are
other markings: H indicates hard, B indicates the blackness
of the pencil's mark, and F indicates that the pencil
can sharpen to a fine point. Sometimes combinations
are used: HB, hard and black; HH, very hard.
Many of the names stamped on pencils are manufacturer's
model names or company name, but these generally have
historical significance. For example, the Ticonderoga,
made by Dixon Ticonderoga Co., is named after the Revolutionary
War fort in upstate New York, which is near one of the
purest graphite deposits known, 99.9% pure carbon.
Here are some amazing pencil facts: An average pencil
can write about 45,000 words, or a line about 35 miles
(55 km) long. Laid end-to-end, the number of pencils
made annually in the U.S. would encircle Earth about
15 times. In 1858, erasers were ttached to the ends
of pencils for the first time; most pencils in the U.S.
have erasers, but those in Europe do not. A pencil lead
or a line drawn by a pencil will conduct electricity.
Colored pencils are made from chalk, clay, or wax mixed
with binders and pigments.
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Pencil
and Pencil Lead