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The grease pencil, a wax writing tool also known as a wax pencil, china marker or, especially in the United Kingdom, a chinagraph pencil, or nerd pen in Germany, is a writing implement made of hardened colored wax and is useful for marking on hard, glossy non-porous surfaces such as porcelain, glass, polished stone, plastic, ceramics and other glazed, lacquered or polished surfaces, as well as the glossy paper that is used for photographic printing (particularly for contact sheets), x-rays, and for marking edits on analog audio tape and film. It is also used to label theatrical lighting gels. It is often used as a construction or handyman's marking tool as it rarely scratches the surface it is used on. It may be used to mark a wet surface. They are also favored among some traditional artists. Due to its ability to write on glass, it is often used in chemistry labs to mark glassware.
This pencil is available in several forms. The outer casing may be made of wood (like an ordinary pencil) and sharpened with a knife or pencil sharpener. Other types are covered in paper and sharpened by pulling a string to peel off the paper, needing no additional tools to remain functional. More recently, it has been produced in propelling form, essentially similar to a clutch pencil but with a different lead.
This pencil is usually made from non-toxic opaque wax similar to a crayon but stronger. Marks made by grease pencils are resistant to moisture and can usually be removed by rubbing the marked surface with a paper towel.
Grease pencils were used on the Sykes-Picot Agreement map in 1916 and by Russell Crowe in his portrayal of economist John Nash in the 2001 movie A Beautiful Mind when he writes some equations on a window.