<Dd> These are pencils that write like pens . The technology was first invented in 1955 by Scripto and Parker Pens . Scripto's liquid graphite formula came out about three months before Parker's liquid lead formula . To avoid a lengthy patent fight the two companies agreed to share their formulas . </Dd> <Dd> Are made of charcoal and provide fuller blacks than graphite pencils, but tend to smudge easily and are more abrasive than graphite . Sepia - toned and white pencils are also available for duotone techniques . </Dd> <Dd> They generally are made of a mixture of clay and lamp black, but are sometimes blended with charcoal or graphite depending on the darkness and manufacturer . They produce a fuller black than graphite pencils, but are smoother than charcoal . </Dd> <Dt> Coloured pencils, or pencil crayons </Dt>

In graphite pencil what does hb stands for