The secondary process of photography

As a result of this trapping of electron holes, there will be enough time for the secondary process of photography to take place. The secondary process involves the reaction between conduction electrons and silver ions to form the silver nuclei of the latent image. Of course, it is conceivable - although rather improbable - that the reaction between the electrons and the silver ions is faster than the trapping of electron holes. In this case, the trapping process would be superfluous. 

When relatively mobile interstitial silver ions (which result from the Frenkel disorder) and conduction electrons from the primary process are available, then the secondary process can occur. This process consists of the reaction of these two species at crystallographically favourable sites [4,5]. It is not possible for submicroscopic silver nuclei to form in undisturbed regions of the crystal. To be sure, josiitral silver atoms can exist on lattice sites or in interstices, but mfijEallknueieL However, these nuclei can form, for example, at jogs on 

In the same way, the sensitizing effect of copper can be formulated by the following overall 

The silver nuclei can also be oxidized if the silver halide is in contact with an external redox system which acts to increase the concentration of electron holes. This process, which is the third important step in the photographic process, is the inverse of the so-called developing process which we shall now discuss. 

When a photograph is developed, the submicroscopic particles grow into visible particles through the action of a reducing treatment. The overall process can be written as  

---