The Dictionary Of Photography

A True Historic Record Of The Art & Practice Of Photography 100 Years Ago.

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Photography in Natural Colours
the direction a b ; and the arrows represent the vibratory motion of the particles of ether, ad or c b is a complete wave length. Now by referring to fig. 103 it is obvious that the point b is exactly half a wave-length from a and c, and c exactly half a wave-length from b and d\ so that we get no light at points which are exactly half a wave-length apart. If a ray of light thus treated passed through a film of sensitive material, it is obvious that where we get no light we shall have no chemical action, and consequently no deposit of silver ; whilst in between these places we shall get a deposit; and a film of this character, after development, will only reflect that light which has a wave-length just double the distance between the reflecting particles of silver ; consequently we get a reproduction of the colour which caused this deposit. Lippmann used first of all Taupenot's albumen process, which consists practically of using iodide of silver sus-pended in albumen ; later he used bromide of silver suspended in albumen ; but he met with one great difficulty, and one which every practical photographer meets with in ordinary practice, and, that is that the silver salts are more sensitive to the blue and violet than to any other colour, or, to put it more popularly, the photographic plate sees the blue and violet as the brightest part of the spectrum ; therefore he exposed his spectrum in sections, using a deep orange-red screen and giving one hour's exposure to get the red, and then five to ten minutes for green with a yellow screen, and a very pale yellow screen and twenty to thirty seconds' exposure for the blue. After exposure the plates were developed with pyrogallol, and fixed, washed and dried. Natu-rally, when the accounts of Lippmann's experiments were pub-lished, and the results confirmed, many attempted to do the same thing. Krone of Dresden was one of the first, and he used albu-men plates, but instead of mercury he used black velvet. M. de St. Florent, in 1892, exposed an ordinary gelatino-bromide plate with an orange screen under a coloured transparency, and then, without developing, fixed and washed it; and it was said this plate whilst damp reproduced the colours. In 1892 MM. Auguste and Louis Lumiere showed at a meeting of the Societe des Sciences Industrielles of Lyons some spectra produced by Lippmann's method which were superior in brilliancy. These were made on gelatino-bromide plates. In 1892 Valenta pub-lished some experiments on the preparation of such an emulsion,