Mechanical pencil applied at an angle. When excess vertical pressure is applied on the lead, the lead is automatically retracted inwards. Higher-end mechanical pencils often feature a lead hardness grade indicator and sometimes feature a retractable lead guide pipe. This allows the lead guide pipe to retract back into the pencil body, which will keep it protected in storage and during transit and makes it 'pocket-safe'. In spite of the name, pencil leads do not contain the toxic chemical element lead, but are typically made with graphite and clay, or plastic polymers. Compared to standard pencils, mechanical pencils have a smaller range
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