Photography: A Very Short Introduction (Very Short Introductions) by Edwards Steve

Author:Edwards, Steve [Edwards, Steve]
Language: eng
Format: epub, mobi
Publisher: Oxford University Press
Published: 2006-08-23T16:00:00+00:00

16. Daguerre, Still Life, 1837

Working in England, Talbot came up with a different process, which, while it did not have the high resolution of Daguerre’s technique, did enable him to produce multiple copies. In many ways, subsequent photographic processes derive from Talbot’s conception of photography. Working on his process from 1833, he began making cameraless contact prints by coating paper with successive treatments of salt and silver nitrate, which reacted to produce light-sensitive silver chloride. He then placed flat, transparent or translucent objects (leaves, plants, lace) directly onto the paper and set them in the sun for a period ranging anywhere from 10 to 30 minutes. Once again, where light passed uninhibited through these objects, the paper darkened; where the light was blocked, the paper retained its original colour. Talbot stabilized the image with a strong salt solution which dissolved the residual silver salts. He called these images ‘photogenic drawings’.

In February 1835, he realized that the process could be repeated by using this first image as a ‘negative’, which could subsequently be used to generate a second ‘positive’ print. (The terms negative and positive were suggested by Herschel, who is usually also credited with coining the term ‘photography’, which literally means ‘light writing’.) Theoretically, this meant that a large number of positive prints could be generated from a single negative and that in these positives the light and dark areas would roughly parallel those in the object depicted. However, at this stage, Talbot’s negatives were insufficiently dense to create strong positive images. In 1840, he discovered a second process, which he called the Calotype (from the Greek word kalos for beautiful and useful). The Calotype process combined silver nitrate with acetic acid and gallic acid, and produced a latent image after an exposure of a few seconds. Talbot treated the outcome with an accelerating agent (gallic acid), enhancing the latent image, this resulted in a negative strong enough to allow further copies to be produced.

Throughout the 19th century, improvements to lenses and better chemical solutions significantly reduced exposure times. However, a central problem still faced photographic experimenters: all these processes were monochrome. Black-and-white photographs register levels of luminosity rather than colours. Experiments with coloured photography have a long and intricate history; here I simply want to indicate some basic principles.

Colour photography is rooted in Sir Isaac Newton’s demonstration that white light can be split prismatically into a rainbow of component colours (wavelengths of light). Colour photographs have, essentially, been made in one of two ways: on the one hand, are those processes that involve breaking down the image into a number of distinct single colour registrations. In this kind of process, three, or sometimes more, monochrome images (typically, a cyan blue image, a magenta image, and a yellow one) are superimposed, or bonded, to create a multi-colour photograph. Processes of this type are known as ‘separation processes’. Photographs in the second category are produced, not by superimposing separate layers, but through chemical reaction. Modern versions of this second technique are

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