Why do some people lick the tip of a pencil before trying to write with it?
#108515. Asked by star_gazer. (Sep 04 09 10:02 PM)
In the old days (before I was born) pencil "leads" weren't as good as they are today. Licking them would make them mark more darkly. Last I checked--not recently--that's still the case with colored pencils.|
Copy and paste from an old (February 9, 1994) MIT source:
A writer to the "How & Why" column in The Boston Globe asked why so many people, before putting pencil to paper, lick the tip? "Is there something about saliva that makes graphite flow better?"
For the answer, which was "yes," the Globe turned to Dr. Jack B. Howard, professor of chemical engineering, who said he himself licks his pencil tip at times.
"If the lead were truly graphite, then wetting it would probably not make a difference," said Dr. Howard, whose research includes work on graphite and other forms of carbon. But in pencil leads, he said, "the graphite is actually a mix of graphite and some clays," which are added to control the hardness of the lead.
"My observation is that wetting the pencil allows you to get a darker line," Dr. Howard said. "There's a softening of the material, some absorption of moisture into pore spaces that makes a mix that will rub off more easily. If it were pure graphite, there would be no pores to let the moisture in."
Is it a safe practice? Yes, said Dr. Howard, the graphite-clay mixture is "perfectly innocuous."
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