|A very brief history, continued 3 of 4|
Fox Talbot's Calotype system was based on a paper negative which needed to be contact printed to a similar piece of sensitized paper to produce the final positive image. This tended to lead to poor quality images even when the negative sheet was rendered translucent by waxing. Glass was the obvious choice for it was cheap and completely transparent but it wasn't until 1851 when Frederick Scott Archer discovered a means of coating a glass sheet (now called a 'plate') with a light sensitive emulsion. His process involved making, exposing then developing the plate while it was still wet - the wet plate process or more correctly the wet collodion process.
The process was not patented which led to its rise in popularity as there were no fees to pay. Once dried the plate would be used to make positive prints on paper, alternatively the glass negative could be bleached so that the dark areas became white, by placing something dark behind it a positive image would be created, these are called ambrotypes.
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