- Education and Science
The History of the Humble Pencil
Pencils are holders of wood, metal or plastic containing lengths of a marking substance, such as graphite. An early assumption that graphite was a form of lead created the misnomer of 'lead pencil'.
In the manufacture of pencils the wood sheath and the graphite compound are made separately and then joined together. The graphite is ground into a very fine powder and is then blended with clay to form a soft mixture. The mixture is forced through dies that shape it into stringy leads of various sizes. After these leads are tempered by baking in kilns at a temperature of 1950° F, they are dipped into wax to give them smoothness for writing.
The hardness of a lead is determined by the proportions of clay and graphite in the lead compound. The more graphite that is used, the blacker and softer the lead. Other elements, such as tallow and wax, may also be added to leads. Colored pencils have leads that are made by mixing coloring materials with clay, chalk, or wax. They contain no graphite and are not baked.
Cedar is the wood most commonly used for making pencil sheaths. It is first seasoned and kiln dried to remove the natural oils. Blocks of cedar of about one pencil's length and seven pencils' width are cut into slats having a thickness of half a pencil. Cylindrical grooves are then carved into each slat. The leads are placed in the grooves of one slat, and another slat is fitted over the leads. The slats are glued together to form a pencil block. The block is cut into sections to form individual pencils, which are then sanded, painted, and varnished.
In ancient times, lead was sometimes used for drawing. When graphite was discovered later, it was often mistaken for lead, and the term "lead pencil" still survives.
In the middle of the 16th century a source of pure hard graphite was found in England. Pieces of this graphite, wound with string or inserted in metal hold ers, made excellent pencils while the supply lasted. During the 18th century the only graphite available was soft and powdery, and various substances were used with limited success to bind it into useful writing implements. In 1795 it was discovered that clay could be mixed with graphite and baked to form a hard, solid material comparable to hard graphite. Soon afterward the modern method of pencil manufacture was begun.
The use of graphite for marking was known to the ancient Aztecs before the Spanish Conquest. Its large-scale use in Europe began with the discovery of an exceptionally pure graphite deposit near Borrowdale, Cumberland, England. First used in chunks graphite was later cut into sticks bound with string. Later still the sticks were inserted into grooves cut into wood, a system first described in 1565.
With the probability of the Borrowdale deposits becoming exhausted attempts were made to reduce the graphite content of pencils by blending the substance with other materials. At the end of the eighteenth century Nicholas-Jacques Conte in France and Joseph Hardmuth in Vienna developed a process for mixing graphite with clay, a technique that is still in use today. The quantity of clay in the mixture determines the hardness, which is a function of its resistance to abrasion by the paper. The density (darkness) of a pencil mark results from the quantity of graphite particles deposited on the paper.
Simple pencils are reusable only by cutting away the wood casing and sharpening the point. The mechanical pencil consists of a plastic or metal case into which a lead is inserted. In propelling pencils leads are inserted into a holder in the casing and propelled towards the point by twisting a part of the casing. Thus, the lead can be exposed for use and withdrawn when not in use.
In clutch pencils the same action is achieved by depressing a knob, which opens the clamp holding the lead; the lead is then fed through either mechanically or manually and the clamp secures the lead again when the knob is released.