Mechanical pencil leads in a limited range of diameters (0.5 mm, 0.7 mm, or 2 mm) for their own products. Koh-i-Noor makes mechanical colored pencils with replaceable leads in 2.0, 3.15 and 5.6 mm sizes. Mechanical pencil A mechanical pencil (US English) or propelling pencil (UK English), also clutch pencil, is a pencil with a replaceable and mechanically extendable solid pigment core called a "lead" . The lead, often made of graphite, is not bonded to the outer casing, and can be mechanically extended as its point is worn away. Other names include microtip pencil, automatic pencil, drafting pencil, technical pencil, click
White lead Other authorities dispute this; the most traditional view is that impermanent pigments and dirty varnish (which is often cleanable) are more likely responsible for darkening. Paintings and the role of varnish, which might protect the white lead yet itself darken, aside—according to Michelle Facini, a paper conservator at the National Gallery of Art, lead carbonate to lead sulfide is indeed what happens to some lead chalks/paints in drawings and watercolors and other works done on paper and unvarnished. Varnish is meant to be removable from an oil painting, to strip off when it dirties or cracks; but on paper it