Formation and Properties of Sub-Image and Latent Image Silver Specks. Part IV. The Formation of Silver Specks—A Process of Nucleation and Phase Formation*

A consequent treatment of the events during exposure or development as a process of phase formation leads to a self-consistent description of the photographic process and many of its details. The supersaturation with respect to electrons produced by exposure or transferred by a reducing agent, determines the energies and rates of formation of silver clusters. It depends on the degree of this supersaturation if a cluster of a certain size grows (by further exposure; during development) or if it decays. [n the former case it acts as an electron trap while in the latter case it captures holes. There does not exist a generally fixed size limit valid for all conditions where, for example, hole capture stops and electron capture commences.The presence of foreign condensation centres (sensitivity specks) changes nucleation from a homogeneous to a heterogeneous process. The formation energies are reduced at such centres; accordingly processes of phase formation take place preferentially at such centres.