needed for forming the Ag₄ clusters that start the autocatalytic process of development. Large crystals will therefore give more sensitive film, for the price of being visibly grainier. Fine grain better preserves details but requires more light.

Tabular-grain film uses crystals of flat morphology, with width-to-thickness ratios of at least two, often much more. The flat morphology allows better overlapping of the crystals, reducing intergranular space and giving more black for the