What is a PENCIL?

A pencil is a writing implement or art medium usually constructed of a narrow, solid pigment core inside a protective casing. The case prevents the core from breaking, and also from marking the user’s hand during use.
Pencils create marks via physical abrasion, leaving behind a trail of solid core material that adheres to a sheet of paper or other surface. They are noticeably distinct from pens, which dispense liquid or gel ink that stain the light color of the paper.
Most pencil cores are made of graphite mixed with a clay binder, leaving grey or black marks that can be easily erased. Graphite pencils are used for both writing and drawing, and the result is durable: although writing can usually be removed with an eraser, it is resistant to moisture, most chemicals, ultraviolet radiation and natural ageing. Other types of pencil core are less widely used. Charcoal pencils are mainly used by artists for drawing and sketching. Coloured pencils are sometimes used by teachers or editors to correct submitted texts but are more usually regarded as art supplies, especially those with waxy core binders that tend to smear on paper instead of erasing.Grease pencils have a softer Crayon-like waxy core that can leave marks on smooth surfaces such as glass or porcelain.
The most common type of pencil casing is a thin wooden Cylinder permanently bonded around the core. Similar permanent casings may be constructed of other materials such as plastic or paper. In order to use the pencil, the casing must be carved or peeled off to expose the working end of the core as a sharp point. Mechanical pencils have more elaborate casings that support mobile pieces of pigment core, which can be extended or retracted through the casing tip as needed.

 Discovery of graphite deposit

Some time before 1565 (some sources say as early as 1500), an enormous deposit of graphite was discovered on the approach to grey knotts from the hamlet of Seathwaite in BorrowDale parish, Cumbria England.The locals found that it was very useful for marking sheep. This particular deposit of graphite was extremely pure and solid, and it could easily be sawn into sticks. This remains the only large scale deposit of graphite ever found in this solid form.Chemistry was in its infancy and the substance was thought to be a form of lead. Consequently, it was called plumbago (Latin for "lead ore") The black core of pencils is still referred to as lead, even though it never contained the element lead and other languages literally mean lead pen.
The value of graphite was soon realised to be enormous, mainly because it could be used to line the moulds for cannonballs, and the mines were taken over by theCrown and guarded. When sufficient stores of graphite had been accumulated, the mines were flooded to prevent theft until more was required. Graphite had to be smuggled out for use in pencils. Because graphite is soft, it requires some form of encasement. Graphite sticks were initially wrapped in string or sheepskin for stability. The news of the usefulness of these early pencils spread far and wide, attracting the attention of artists all over the known world.
Although deposits of graphite had been found in other parts of the world, they were not of the same purity and quality as the Borrow dale find, and had to be crushed to remove the impurities, leaving only graphite powder. England continued to enjoy a monopoly on the production of pencils until a method of reconstituting the graphite powder was found. The distinctively square English pencils continued to be made with sticks cut from natural duck graphite into the 1860s. The town of Keswick, near the original findings of block graphite still manufactures pencils, the factory also being the location of the Cumberland pencil museum.
The first attempt to manufacture graphite sticks from powdered graphite was in Nuremberg, Germany, in 1662. It used a mixture of graphite, sulphur, and antimony
Residual graphite from a pencil stick is not poisonous, and graphite is harmless if consumed.
  
Manufacture

Modern pencils usually do not contain lead as the "lead" of the pencil is actually a mix of finely ground graphite and clay powders. Before the two substances are mixed, they are separately cleaned of any foreign matter and dried in a manner that creates large square cakes. Once the cakes have fully dried, the graphite and the clay squares and are mixed together using water. The amount of clay content added to the graphite depends on the intended pencil hardness (lower proportions of clay makes the core softer), and the amount of time spent on grinding the mixture determines the quality of the lead. The mixture is then shaped into long spaghetti-like strings, straightened, dried, cut, and then tempered in a kiln. The resulting strings are dipped in oil or molten wax, which seeps into the tiny holes of the material and allows for the smooth writing ability of the pencil. A juniperor incense Cedar  plank with several long parallel grooves is cut to fashion a "slat," and the graphite/clay strings are inserted into the grooves. Another grooved plank is glued on top, and the whole assembly is then cut into individual pencils, which are then varnished or painted. Many pencils feature an eraser on the top and so the process is usually still considered incomplete at this point. Each pencil has a shoulder cut on one end of the pencil to allow for a metal ferrule to be secured onto the wood. A rubber plug is then inserted into the ferrule for a functioning eraser on the end of the pencil.