Pencils

As a writing tool, pencils are a quite recent invention and their widespread use can be attributed to discovery of graphite and industrial revolution of 17th-18th century. Pencils are made up of a soft graphite core which is surrounded by wood or plastic for protection. Graphite is used along with a clay pigment which leaves permanent marks which can be erased easily with the help of an eraser. Pencils are used in schools, for art and drawing, for diagrams as unlike pens their marks can be erased easily and this provides a user plenty of room for correcting any inadvertent mistake committed without starting from scratch again. Shade and darkness of a pencil can vary greatly depending on the type of graphite or pigment used and there are separate classes of pencils available for drawing, technical art, writing etc. A scale known as HB where H stands for hardness and B stands for blackness is used for differentiating various types of pencils from each other.