Early Photographic Techniques

The evolution of photography in the nineteenth century witnessed the development and improvement of a variety of photographic processes.

Initially the Daguerreotype, announced by Louis Daguerre in 1839, was an extremely hazardous process which used a potentially lethal combination of chemicals. A highly polished silver plate coated with silver iodine was exposed in a camera for anything up to thirty minutes, then fumed with mercury vapour and fixed by a solution of common salt to produce an image. The making of multiple copies was not feasible and in Europe the process had fallen into disuse by the mid 1850's.

The Calotype was devised by Henry Fox Talbot and introduced very soon after the announcement of the daguerreotype in 1839. It involved the use of writing paper sensitised with common salt and silver nitrate which produced an negative image by exposure to light which in turn produced a positive when printed in contact with another sensitised sheet. This is the basis of all subsequent negative/positive photography. This process was easy to handle but initially exposures could take hours. Eventually exposure times were reduced to a few minutes. Unlike the daguerreotype, the negative image could be reproduced on paper as a positive any number of times.

The Wax Paper process was an improvement on the calotype process which printed the paper texture of the negative, giving a gritty appearance. Waxing the paper before placing in the sensitising solution prevented the silver salts from penetrating the paper and produced a smoother and sharper image. This was Mary Rosse's favourite process as the paper could be prepared in the darkroom and kept for up to a week before use. It was light and easy to carry and the negatives could be developed at a convenient time later in the day.

The Wet Collodion process used a glass plate coated with collodion (gun cotton dissolved in alcohol and ether) followed by immersion in the silver nitrate solution. The new coating on glass was two hundred times more light sensitive than the calotype leading to shorter exposures of about 10 seconds which made portraiture more comfortable. The exposed plate had to be developed within 10 minutes, before it dried. Various designs of portable darkroom were invented to make location photography possible. The procedure was smelly, used potassium cyanide as a fixer and stained fingers and clothes.

Process of Stereo Photography

Stereoscopic photographs reproduce the three dimensional effect of vision by taking two slightly different views as seen by each eye. The optical centres of the lenses are separated by the same distance as that of the eyes. This was first demonstrated by Sir Charles Wheatstone in 1838, just before the announcement of photography, by using specially prepared drawings.

The Latimer Clark-pattern stereoscopic camera was designed to use wet collodion plates and has only one lens. In order to obtain the two negatives it was necessary to move the camera from left to right between exposures and then push across the plate holder prior to exposure of the second image. The Countess took many of her early photographs using this camera.

The earliest stereo cameras had only one lens and a lateral shift mechanism necessitating two sequential exposures, making photographs of living subjects very difficult. By the late 1850's cameras having two matched lenses enabling both negatives to be exposed simultaneously were introduced, a move that led to widespread demand for stereoscopic photographs.

Colour Synthesis

The reproduction of colour in photography is based on the fact that sensors in the eye respond to the three primary sectors of the visible spectrum; red, green and blue. Any colour can be synthesised by mixing light in proportions of each of these primary colours. John Joly accomplished his colour reproduction on a single plate by using a screen with the primary filters applied in narrow strips, in contact with the photographic plate. When the resulting transparency was projected through a colour screen and viewed at a suitable distance the red, green and blue sectors merged, recreating the original colours. Colour television uses the same principle, employing red, green and blue phosphors which merge when viewed at the correct distance.

The process of additive synthesis is created when three separate black and white photographs are made using red, green and blue filters. Positive transparencies are made of each and then projected through a filter of the colour used during exposure. A triple projector is used to superimpose all three images on the screen resulting in a full colour representation of the scene.

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