Tabular Crystals
In panchromatic emulsions, the sensitivity of the silver halide crystal is enhanced by sensitizing dyes that adsorb on the crystal surface. Therefore, sensitivity can be increased by adsorbing more sensitizing dye. This requires increasing the surface area of the crystal, and also improving the dye molecules to form a dense assembly of the dye molecules. Tabular grain emulsion solves the first part of this problem.
Tabular crystals tend to lie along the film's surface when coated and dried. This reduces scattering of light and increases resolution.
Tabular crystals usually have two twinned planes parallel to each other. They are formed at the very beginning of the crystallization. The crystal tends to grow at the edges and not on the main planes, forming very thin crystals of very large surface areas. Tabular crystals probably existed from very early days of silver-gelatin photography. However, it was about 1970 when emulsion engineers could make emulsions that consisted mainly of tabular crystals. Moreover, it was not until the 1980s that tabular crystals began to be used in production emulsions.
Tabular grain technology brought significant improvements to the image quality of the film, particularly in the improvement of resolution and granularity. However, several more key technologies were implemented into tabular grain products. Many of these concurrent improvements were applied to non-tabular grain products to improve image quality. Therefore, when tabular grain technology is described by uninformed writers, its advantage tends to be overemphasized. For example, excellent reciprocity law is not an inherent property of tabular crystals but rather the result of other techniques introduced at about the same time.
Read more about this topic: Tabular-grain Film
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