A pencil may be an implement or art medium constructed of a narrow, solid pigment core inside a protective casing which prevents the core from being broken and/or from leaving marks on the user’s hand during use. Pencils create marks by physical abrasion, forgoing a trail of solid core material that adheres to a sheet of paper or another surface. They're distinct from pens, which instead disperse a trail of liquid or gel ink that stains the sunshine colour of the paper by absorption. The most common sort of pencil casing is of thin wood, usually hexagonal in section but sometimes cylindrical, permanently bonded to the core. Similar permanent casings are also constructed of other materials like plastic or paper