A photocopier is a machine which makes paper copies of documents and other visual documents quickly, easily and cheaply.

Most modern photocopiers use a technology known as xerography. Photocopiers have a cylindrical drum inside them and this is given an electrostatic charge. The photocopier drum is coated with a photoconductive material such as selenium and this becomes conductive when exposed to light. A bright light is then shined onto the original document and the white parts of the document reflect the light back onto the photoconductive drum. The bits of the drum that are exposed to the light become positively charged and the bits of the drum not exposed to the light become negatively charged. This means that an electrical image of the document is left on the drum.

Photocopier toner is postively charged. When it gets applied onto the drum, it sticks to the negatively charged parts of the drum. The toner image is then transfered off the drum onto a new sheet of paper. Heat is applied to the paper to melt the toner and bond it to the paper. The drum is then wiped clean with a rubber blade and the next sheet can then be copied.

Xerox were the first company to introduce the xerographic photocopier to the world in 1949. Their photocopier became so popular that the term ‘Xeroxing’ became synonymous with the term ‘photocopying’.

Recently, there has been a different technology on the market - digital technology. Photocopiers basically scan the sheet of paper and print it out like a laser printer. This means that the photocopier will generally have better quality photocopies and it can build jobs more easily. It can also do multiple sets more quickly because it only has to scan each original document once.

Some photocopiers are purely black and white, some photocopiers are colour. Colour photocopier toner tends to be more expensive than black photocopier toner.

Photocopiers each have ‘fingerprints’ which can be used in forensic science. The mechanics of the paper feed mechanisms and toner feeds cause ‘banding’ which means photocopied paper can usually be identified to particular brand and model. Some high quality photocopiers also leave a small section of nearly invisible yellow dots on paper so that photocopies can be traced and track in the case the counterfeiting is found.

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