jan 1, 1790 - Thomas Wedgwood (England): first person reliably documented to have used light-sensitive chemicals to capture silhouette images on durable media such as paper, and the first known to have attempted to photograph the image formed in a camera obscura.

Description:

In his many experiments, possibly with advice on chemistry from his tutor Alexander Chisholm and members of the Lunar Society, Wedgwood used paper and white leather coated with silver nitrate. The leather proved to be more light-sensitive. His primary objective had been to capture real-world scenes with a camera obscura, but those attempts were unsuccessful. He did succeed in using exposure to direct sunlight to capture silhouette images of objects in contact with the treated surface, as well as the shadow images cast by sunlight passing through paintings on glass. In both cases, the sunlit areas rapidly darkened while the areas in shadow did not.

Wedgwood was unable to "fix" his pictures to make them immune to the further effects of light. Unless kept in complete darkness, they would slowly but surely darken all over, eventually destroying the image. As Davy put it in his paper of 1802, the picture, immediately after being taken, must be kept in some obscure place. It may indeed be examined in the shade, but in this case the exposure should be only for a few minutes; by the light of candles and lamps, as commonly employed, it is not sensibly affected.

Although unfixed, photographs such as Wedgwood made can be preserved indefinitely by storing them in total darkness and protecting them from the harmful effects of prolonged open exposure to the air—for example, by keeping them tightly pressed between the pages of a larger book.

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