The Dictionary Of Photography

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

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Development and Developers
there is a general reduction of the silver salt; this general re-ducing action is, however, less, if some soluble bromide be added to it. Frequently a sulphite is added to a developer, and this is useful in that it prevents the too rapid oxidation and consequent discoloration of the developing agent, and thus prevents stain-ing of the hands and the gelatine of the film. Having thus far considered the main points of development we may consider the chemical theory of the same to be as follows : - The latent image, which we will assume to be sub-bromide of silver, Ag2Brt is split up into metallic silver and bromine ; the bromine is at once absorbed to form bromide of the alkali or some more complex compound, the reducing agent or developer proper being oxidised; but if the action were to cease at this point, the
Fig. 42.
image would be very faint; the metallic silver and the unacted-on bromide of silver react and form more sub-bromide, which is again reduced by the developer to the metallic state. Some particular modifications of the various developers and methods of development applied to special purposes are to be found under various headings, as Bromide Paper, Wet Collodion, Artigue's Process, Carbon Printing, Enlarging, Gelatino-Chloride Emulsion Paper, etc. As regards the development of ordinary dry plates, sufficient for the general guidance of the beginner, and hints for the advanced worker generally, will be found in this article; but some special matters relating to the development of gelatino-bromide dry plates will be found under such headings as Hydroquinone and Eikonogen. It is important to remember that tha influence of temperature on development is so great that the same chemicals will give very different results