Pencil core is made of a graphite and clay powders. The amount of clay content added to the graphite depends on the intended pencil hardness and the amount of time spent on grinding the mixture determines the quality of the lead. The resulting strings are dipped in oil or molten wax, which seeps into the tiny holes of the material and allows for the smooth writing ability of the pencil.Many pencils feature an eraser on the top and so the process is usually still considered incomplete at this point. Each pencil has a shoulder cut on one end of the pencil to allow for a metal ferrule to be secured onto the wood. A rubber plug is then inserted into the ferrule for a functioning eraser on the end of the pencil.