The Electron Microscopy of Photographic Grains. Specimen Preparation Techniques and Applications

Several electron microscopical specimen preparation techniques are described, including two replica techniques. The most important specimens utilize the thin film of the silver-gelatin complex which exists as a tightly fitting skin around the photographic grains. This relatively inert and insoluble complex is referred to as the combined envelope; a study of this structure is given. Latent image centers are enlarged in several ways so as to be readily resolvable in the electron microscope. After this partial development the matrix or intergrain gelatin is removed and the grains are fixed. The final specimen consists of developed centers retained by the combined envelope. Applications of the replica technique to grain shape, size distribution, and growth nature of photolytic silver are given. Utilization of the combined envelope in conjunction with the special development techniques to provide information which substantiates independent sensitometric data is also demonstrated.