The Dictionary Of Photography

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

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Ferricyanide of Copper
For sensitising the paper or materials solutions IV. and V. or V. and VI. may be mixed in equal parts. The paper is impregnated with the desired mixture, dried, and then exposed under a nega-tive for ten or fifteen minutes, and after exposure washed in dilute hydrochloric acid, and finally with water, and dried. Feer has lately suggested diazo-pseumocumidine sulphonate, and this, withand sodium hydrate, gives scarlet-red images ; by
replacing thewithviolet images are
obtained, and by using resorcinol orange colours are obtained.
Ferricyanide of Copper, Toning by. See under Bromide Paper.
Ferroprnssiate Processes. See Cyanotype.
Ferrotypes. Positives taken by the wet process on thin iron plate, which is coated with brown or black varnish. As the pro-duction of these is exactly the same as the production of collodion positives on glass, instructions are given for this under Wet Collodion {q.v.). Ferrotype plates coated with a thin film of a highly argentiferous gelatine emulsion have been introduced commercially for use with a semi-automatic camera, like that of Mr. Nievsky, and which is described under the heading Automatic Photography. A much better ferrotype dry plate, esteemed by those itinerant professional photographers who use the automatic camera out of doors, is one coated with a collodion emulsion film, and put on the market by Mr. Nievsky.
Ferrons Oxalate Developer. See Developer; also Bro-mide Paper.
Ferrons Salts. See Iron and its salts.
Field of a Lens is the illuminated circle given by the lens, the diameter of which is usually expressed in degrees, but, as we have already noted, is conveniently expressed in terms of the focal length. The extent of surface which a lens will cover is independent of the diameter of the diaphragm aperture, but the area of sharp focus is affected by the diameter of the stop. (See also Angle of View.)
Filigrane. This term is applied by the French to that which we call the water-mark of paper, and Mr. W. B. Woodbury