Henry Petroski, that most excellent of engineering writers, uses the pencil as a metaphor for the study of the engineering process in his first-rate history The Pencil.- A History of Design and Circumstance. The pencil represents innovation, ingenuity and inventiveness.
The problems facing a pencil engineer are similar in concept to those of an engineer building a bridge. The pencil lead must be created in such a manner so that it will be strong enough to remain sharp as long as possible and strong enough not to break. This requires special mixtures of clay and graphite, proper baking temperatures and pressures. The bridge engineer must also seek the proper balance between competing materials and methods of construction for the best balance of price and strength (see Petroski's other book on bridge building and accidents, To Engineer Is Human: The Role Of Failure let Successful Design TA174.P474 1992); it is not always easy to predict how combinations of materials will perform.
The common inexpensive pencil we take for granted actually requires an exacting manufacturing process to create and uses many different materials from around the world. "The lead... might be a proprietary mixture of two kinds of graphite, from Sri Lanka and Mexico, clay from Mississippi, gums from the Orient, and water from Pennsylvania. The woo den case would most likely be cut from western incense cedar from California, the ferrule possibly of brass or aluminum from the American West, and the erase perhaps manufactured using a mixture of South American rubber and Italian pumice stone."
Actually, the "lead" pencil of today contains no lead, not even in the paint on the outside. The writing material is a mixture of:: graphite, clay, and other ingredients. The most famous graphite came from a single source in the British Isles, and it was so valuable that workers mining the material were required to strip down as they left the mine through several vaulted and locked rooms to prevent theft. The depletion of the mine was a source of great consternation until substitute materials were found.
The pencil got its name from the Roman fine-pointed brush called apenicillus. It was created by inserting a tuft of animal hairs into a hollow reed, later called by the diminutive penis, Latin for tail, hence a little tail used for drawing fine lines.
So, through the history of this little tool, Petroski celebrates the engineer as the innovator and amalgamator of the practical and the theoretical.
