What is photocopying?
- Broadly, photocopying is a set of techniques used to duplicate content using, among other things, light.
- However, the contemporary colloquial use of the word ‘photocopying’ refers almost exclusively to xerography.
- Both the word ‘xerography’ and the name ‘Xerox’ come from the Greek rootword ‘xero’, meaning ‘dry’.
- This is because xerography is a type of photocopying method where the process doesn’t involve messy liquid chemicals.
- Xerographic machines are in ubiquitous use around the world today to quickly and cheaply reproduce printed material.
How does xerography work?
- Xerography has a few basic elements.
- The first is the photoconductive surface a surface coated with a photoconductive material.
- Such a material, when exposed to light, allows electrons to flow through it (that is it conducts electricity) but blocks them when it’s dark.
- This surface is negatively charged by placing a thin negatively charged wire with a high voltage next to it.
- Then, the sheet of paper to be copied is illuminated with a bright light.
- The darker parts of the paper where something is printed don’t reflect the light whereas the unmarked parts do.
- This reflected light is carried by lenses and mirrors to fall on the photoconductive surface.
- In the parts of the surface where light falls, the photoconducting material will become conductive and allow the electrons near its surface to dissipate downwards (into a grounding).
- So the parts that remain negatively charged at the end of this step will correspond to parts of the papertobecopied (TBC) where something was printed.
Who invented xerography?
- Inspired by the work of the Hungarian engineer Paul Selenyi, an American attorney named Chester F. Carlson came up with a rudimentary version of xerography by 1938.
- Seven years later, he sold his idea to a nonprofit organisation called the Battelle Memorial Institute in Ohio, where researchers refined the technique.
- A year later, in 1946, the small New Yorkbased Haloid Photographic Company purchased a licence from Battelle to build a machine based on the technique.
- The company trademarked the name for this machine as the “Xerox machine” in 1948 and availed the first model for sale in 1949.
- Haloid’s managers were responsible for coining the word ‘xerography’, replacing Carlson’s ‘electrophotography’.