International Year of Chemistry 2011: Photography: The Chemistry of an Image

Abstract

The wish to reproduce permanently an image from nature is very old. Camera obscura , a darkened chamber or box with a pinhole, was known since Hellenistic times. It allowed projection of inverted images onto walls or screens. In the 16th century, lenses were mounted in front of camera obscuras' apertures, and the devices were made portable. Masters, such as Johannes Vermeer working in Holland in the 17th century and later Canaletto in Italy, used camera obscuras to reproduce in their paintings the effects of light as well as minute details. The images produced by these devices were, however, not permanent. In the 1720s a German physician, Johann Schulze (1687–1744) reported that a mixture of chalk and silver nitrate would darken if left in sunlight but not when it was heated. In Britain, Thomas Wedgwood (1771–1805; the son of Josiah Wedgwood, the founder of famous Wedgwood pottery) and Sir Humphry Davy (1778–1829) obtained silver nitrate images on leather and on paper but could not make them permanent. Photography as we know it developed in the first half of the 19th century amidst considerable excitement and competition. The French inventor Joseph Nicephore Niepce (1765–1833) obtained a reasonably permanent image while experimenting with lithography. He placed an oiled drawing on a plate coated with bitumen of Judea—a form of asphalt that hardened …