Art in this area is represented by lines made on a surface with a pencil or pen. The pencil is an instrument of graphite enclosed by a wood casing. Effects of the pencil may be changed or highlighted with a cloth such as chamois or a simple eraser. Pen and ink drawings are typically done with black carbon ink (examples are Chinese or India ink), brown ink, or chemical ink. Three pen types used are quill, reed, and metal. Quill pens were most popular for their flexibility and ability to be sharpened to extreme fineness. Steel became the predominant pen type by the 20th century. Both pencil and pen drawings are done almost exclusively on paper.