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
and a year later the brothers Lumiere published their formula. Valenta's process is as follows : -
A.                                                      B.
Gelatine ......      10 gm.            Gelatine ...... 20 gm.
Water ......    300 c.cm.         Water ...... 300 c.cm.
Silver nitrate ...         6 gm.           Potassium bromide 5 gm.
The solutions should be cooled to 30o-35o C, and then solution A gradually added to solution B, with constant stirring, and a faint opalescent or almost transparent liquid is obtained, which is immediately poured into about 1 litre of 90 per cent, alcohol, and well stirred till the gelatine emulsion clings to the glass rod. It is then cut up into small pieces, washed in running water for a short time, and made up to the original bulk (600 c.cm.) with water, melted and filtered, for which purpose Valenta strongly recommends fine Italian hemp, well washed with caustic potash and water or glass wool. After filtration the emulsion is colour-sensitised with some dye and coated. Valenta states that, after the emulsion has set, the plates should be soaked in dilute alcohol, and rocked till the small air bubbles, which adhere very firmly to the film, are no longer visible. They should then be washed under a tap, and dried. To render these plates colour-sensitive alcoholic solution of cyanine 1 : 500 is used, and either 1-2 c.cm. of this is added to every 100 c.cm. of emulsion before coating, or the plates can be bathed after coating in a bath of 1-5 c.cm. of above, solution in 100 c.cm. of water. Better results are obtained by mixing cyanine and erythrosin as follows : Cyanine solution (1 : 500) 4 c.cm., erythrosin solution (1 : 500) 2 c.cm.; and of this mixture 1-2 c.cm. can be added to every 100 c.cm. of emulsion. Vogel's azaline may be used in the same proportion. The silver salts of eosine have been very successful in reproducing mixed colours. Valenta gives the two following chloro-bromide emulsions as also giving good results, particularly with the less refrangible rays, but cannot state which is the better : -
A.
Water ...... 200 c.cm.
Gelatine ... 10 gm.
I.
B.
Water ...... 15 c.cm.
Silver nitrate ... 1*5 gm. 491