It must be remembered that photographic products were developed largely for use in the Euro-American world. They needed special handling in Tibet where, for example the quality of light, caused problems of exposure time for photographers.
Glass plates featured here are gelatin dry plates in which the light sensitive silver halides were distributed across the plates in a gelatin solution. By the mid twentieth century and vast range of negatives, of different sizes and sensitivities was available. These were factory made and standardised. A wide range of plates is present in the Tibet collections. Even those which are predominantly glass plate, such as the Charles Bell collection, use a variety of plate types of different sizes and speeds. They will have been specially selected by their users to respond adequately to the subject matter in the difficult conditions encountered in Tibet.
Despite Bell's use of glass plates, by the 1920s they were largely superseded by film negatives which varied in size according to the camera used. Again a wide range of different kinds was available. Typical of the date, those made in the 1920s and 1930s have cellulose nitrate film base, which carried the light sensitive chemicals. Later negatives, such as those of Hugh Richardson, have an acetate base.
Most of the prints featured here are various forms of the standard silver gelatin process using develop-out-papers which were almost universal by the dates in question. The prints are either contact prints, that is made by direct contact with the negative and thus the same size as the negative, or enlargements from negatives, as was common practice. The differences in size between print and negative will indicate this latter process. All are printed in black and white with no colour toning.
There are two types in the collection. The earlier ones, from Spencer Chapman, are made by the Dufay Colour process, which was the first easily available colour process for the amateur. It was colour screen process in which the colour particles were held in a network on the film base. These films were rather slow and this will have influenced the subject matter chosen for colour recording in Tibet. (Considerable digital intervention to remove the distracting network or réseau has been done on images on the website.) It was possible to print from Dufay Colour, but the results were not good. The later transparencies by Richardson are in the standard 1950s and 1960s 35mm Etkachrome and Kodachrome processes and a number of them are copy slides of the earlier colour material.
Lantern Slides are positive images made by a variety of processes, often collodion based, from both negatives and prints in order to be able to project the image for viewing. The image is usually mounted between thin pieces of glass to the standard size of 3 1/4 inches square. (8.3 cm) Often used for educational purposes, this format is important because it indicates the intention of the choice to use the image in a specific way, that is, to communicate ‘Tibet' to an audience.
Elizabeth Edwards (Professor, University of the Arts, formerly head of Photograph Collections at the Pitt Rivers Museum)
Gordon Baldwin, Looking at photographs: a guide to technical terms
(Malibu/London: J. Paul Getty Museum in association with British Museum Press, 1991)
Jack Coote, The Illustrated History of Colour Photography (Surbiton: Fountain Press, 1993)
Robin Lenman (ed), The Oxford Companion to the Photograph (Oxford: Oxford University Press 2005) various entries.