Pencil sharpener pencil in position, although they then sharpen them to the usual conical point as for a round pencil, abandoning some distinctive aspects of the carpenter's pencil. Sharpeners with a single blade for use on wax crayons are available, and sometimes included in boxes of crayons. These often have plastic blades, which are adequate for the soft wax. Mechanical pencils dispense the graphite lead progressively during use and thus do not require sharpening; such pencils are sometimes called "self-sharpening". A type of mechanical pencil has a rotating gear mechanism which rotates the lead slightly every time the lead is lifted off
White lead for bearings and in machine shops. What is commonly known today as the "Dutch method" for the preparation of white lead was described as early as Theophrastus of Eresos (ca. 300 BC), in his brief work on rocks or minerals, "On Stones" or "History of Stones." His directions for the process were repeated throughout history by many authors of chemical and alchemical literature. The uses of cerussa were described as an external medication and pigment. Clifford Dyer Holley quotes from Theophrastus' "History of Stones" as follows, in his book "The Lead and Zinc Pigments". Lead is placed in earthen vessels