in 1829, the two working on methods of producing an image. Niepce died before he saw the results of their labours but Daguerre went on to find a way of fixing a reproduced image, called by its inventor the Daguerrotype.
A copper plate was covered with a thin coating of silver which was then polished to a high shine. It was then treated with iodine which produced a light-sensitive layer of iodide. The plate was exposed in a camera and the image brought out by the action of mercury vapour. Stopping the chemical action and fixing the image was a problem at first solved by use of common salt. But later Daguerre found 'hypo' (sodium thiosulphate) to be a better fixing agent.
The daguerrotype was a negative image but when viewed at the right angle the negative appeared positive. The picture was faint but well defined..
Early daguerrotypes took time to expose. This made it difficult to photograph anything other than still scenery. People or animals moving in the picture showed up only as a blur. However, other photographers introduced improvements. Bromine was found to act as an accelerator speeding up the process, so that exposure times were reduced to a couple of minutes by the early 1840s. Portraiture thus become possible and an entire new industry was born.
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