The chemical process
- In the 1600s Robert Boyle, a founder of the Royal Society, reported that silver chloride turned dark under exposure but believed this was caused by exposure to the air.
- Angelo Sala in the early 17th Century noticed that powdered nitrate of silver was blackened by the sun.
- In 1727 Johann Heinrich Schulze discovered that certain liquids change colour when exposed to light.
- At the beginning of the 19th Century Thomas Wedgwood successfully captured images, but his silhouettes could not survive because he didn’t know how to make the image permanent.