Some Basic Concepts of Photographic Development

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Abstract
In contact with a redox system like a developer, silver bromide shows n-type semiconductivity. From this, the rate of electron injection during the development is calculated. It is shown that only surface centres can be reduced. Therefore the electrode theory of development is valid for the primary stages of development too. The development centre as a surface state and its stability against a redox system is discussed in view of the theory of semiconductor electrodes. The effect of developer adsorption at the nucleus upon the kinetics of development is doubtful, with the exception of the phenomenon of superadditivity. Space charges within the grain influence the situation of the latent image in the grain, but their effect upon development seems to be small. The electrochemical kinetics of physical development are derived, especially for the case of diffusion controlled reactions. In chemical development etching and reduction occur at the same place of the grain unless inhibition effects are significant. The size and stability of the filamentary silver is dependent on the potential and on adsorption phenomena at the metal surface. The publications of recent years which are of special interest for the mechanism of single grain reduction are discussed.

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