Graphite pencils are the most common types of pencil, and are encased in wood. They are made of a mixture of clay and graphite and their darkness varies from light grey to black. Their composition allows for the smoothest strokes. Solid graphite pencils are solid sticks of graphite and clay composite (as found in a ‘graphite pencil’), about the diameter of a common pencil, which have no casing other than a wrapper or label. They are often called “woodless” pencils. They are used primarily for art purposes as the lack of casing allows for covering larger spaces more easily, creating different effects, and providing greater economy as the entirety of the pencil is used. They are available in the same darkness range as wood-encased graphite pencils. Carbon pencils are generally 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. Coloured pencils, or pencil crayons have wax-like cores with pigment and other fillers. Multiple colours are often blended together. Watercolour pencils are designed for use with watercolour techniques. The pencils can be used by themselves for sharp, bold lines. Strokes made by the pencil can also be saturated with water and spread with brushes.