A photocopier is a reproduction device that utilizes the principle of electrophotography to create duplications of source documents. The process involves charging a photoconductive surface, such as a drum, and then using an image source to selectively discharge the charge in patterns corresponding to the original text or image. A fine powdered pigment, or toner, adheres exclusively to these charged areas. Once the image is captured, the toner is transferred from the drum onto a receiving substrate, typically paper. To make the transfer permanent, the substrate passes through a fusing unit that applies localized heat and pressure, melting and bonding the pigment particles to the paper surface to form a solid, repeatable copy.