Pencil sharpener of 6 cuts and takes practice to master without breaking the lead. Specialized sharpeners are available that operate on non-standard sizes of pencil, such as crayons used in primary schools. Sharpeners that have two openings, one for normal pencils and one for larger crayons, are fairly common. An artist's or draftsman's pencil sharpener leaves the graphite untouched and sharpens only the wood (some models can switch from standard to wood-only by an adjustment). The graphite lead is then honed to a sharp point with a lead pointer, which sharpens only the lead without wood. Lead pointers are also used with
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