Pencil, from Old French pincel, from Latin penicillus a "little tail" (see penis pincellus is Latin from the post-classical period ) originally referred to an artist's fine brush of camel hair, also used for writing before modern lead or chalk pencils. Old Soviet colored pencils with box (circa 1959) Camel's hair These casings can be reloaded with new cores (usually graphite) as the previous ones are exhausted. Mechanical pencils have more elaborate casings which are not bonded to the core instead, they support separate, mobile pigment cores that can be extended or retracted (usually through the casing's tip) as needed. To use the pencil, the casing must be carved or peeled off to expose the working end of the core as a sharp point. Casings may be of other materials, such as plastic or paper. The most common pencil casing is thin wood, usually hexagonal in section but sometimes cylindrical or triangular, permanently bonded to the core. Grease pencils have a softer, oily core that can leave marks on smooth surfaces such as glass or porcelain.
Coloured pencils are sometimes used by teachers or editors to correct submitted texts, but are typically regarded as art supplies, especially those with cores made from wax-based binders that tend to smear when erasers are applied to them. Other types of pencil cores, such as those of charcoal, are mainly used for drawing and sketching. Graphite pencils (traditionally known as "lead pencils") produce grey or black marks that are easily erased, but otherwise resistant to moisture, most chemicals, ultraviolet radiation and natural aging. Most pencil cores are made of graphite powder mixed with a clay binder. They are distinct from pens, which dispense liquid or gel ink onto the marked surface. Pencils create marks by physical abrasion, leaving a trail of solid core material that adheres to a sheet of paper or other surface.