Ask A Scientist Chemistry Archive

name         Garrett
status       student
grade        4-5
location     OH

Question -   My dad told me that a no. of a pencil depends on the kind
of 'lead' in a pencil. What is in a
No. 3 pencil?
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All the kinds of lead are a bake-dried paste
made of gray carbon powder plus some soft whitish stone powder.
The difference is the percentage of each.

The dark gray color dominates the dried brittle pencil-lead,
so you never notice any whitish color or lighter gray.

The main effect of the stone powder is:
when packed together, it is harder than pure graphite carbon.
Pure graphite carbon powder sometimes seems as soft as
a silvery-gray wax crayon.
The stone powder can be stronger, like partly-fired clay.

More stone powder makes a harder lead and is labeled with higher numbers,
like #3 or #4.
Less stone and more soft dark graphite carbon makes a lower number,
like #1 or #2.

I think about all there is to it,  Garrett.
Perhaps you can find recipes for pencil lead on the Internet.

Jim Swenson
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Garrett,
One of the most popular tools for writing is the pencil.  Pencil marks, 
unlike those made by writing implements using fluids, can be easily 
erased.  In 1795 a way was devised of mixing powdered graphite with clay, 
cutting the resultant mixture into strips and then baking it.  The 
hardness of these pencils depends on the proportion of graphite to 
clay.  The more graphite used, the softer or darker is the mark made. In 
1812, an American named William Monroe invented a process still used today 
by which the graphite-clay mixture could be encased between two pieces of 
cedar wood. Taken from ENCARTA DVD 2005.  I hope that this helps.

Sincerely,
Bob Trach
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