 How Does a Pencil
Write?
This may sound like a silly question because
most of us have taken a pencil and many everyday objects for
granted. A pencil is very suitable for making temporary notes
because its markings are easily erasable.
The core of your pencil is not made from
lead. At one time though, people may have written with pieces
of lead, a poisonous metal.
The modern version of this writing instrument
was first devised by French inventor Nicholas-Jacques conte'
at about 1790. A cylinder of "lead", made by mixing graphite
with clay and fired within a kiln, forming the pencil's core
was encased within a wooden shaft. Varying amounts of clay
changes the hardness of the "lead" in your pencil. Swedish
chemist Carl Wihelm Scheele showed graphite, in 1779, to be
a form of carbon.
 Activity
I
The lamellar crystalline structure of graphite is responsible
for its greasy, lubricating feel. When you are writing with
a pencil, you are actually peeling microscopic sheets of graphite
and depositing them on your paper. The particle size and number
of particles deposited on the paper determines the darkness
of the pencil marking.
Take out a sheet of paper and draw three lines (1 thin, 1 thick,
1 retraced 6 times) on it with a sharpened pencil. Can you describe
the color, darkness and other qualities of these markings? Inspect
the lines under an optical microscope. Compare and contrast
the lines. At higher magnifications, do the lines appear alike
or different? Are they continuous? what is the substance that
is causing the color of the line?
 Activity
II
On another area of the same sheet of paper used above, rub
the pencil on the paper to form a wide patch. Get an Ohmmeter
and place its probes on different locations along the lines
and within the patch. Do the markings conduct electricity? How
does the electrical resistance of the lines and patch compare?
 Activity
III
Pick up the pencil and feel the core of the pencil. Also pick
up a piece of pure graphite. Notice what you feel. Can you explain
why they feel that way? Clay was mixed with graphite to form
the pencil's core. What do you think the clay is used for? Writing,
drafting, and drawing pencils have number designations that
tells about the hardness of the pencil core. What is hardness
and can you devise a way to determine this physical property?
The physical properties of graphite that you have observed
is determined by how its atoms are arranged to form a crystalline
structure. Can you rationalize the physical properties of graphite
based on the images given here?
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