When fine-grain photographic emulsions were developed, separated spheres or ellipsoids of silver were produced. The colour and covering power of the silver depended sensitively upon the sizes and shapes of the particles. A good understanding of the absorption curves for yellow, green, and neutral silver was obtained by applying the Mie and Cans theories to the sizes and shapes of silver particles which were observed in electron micrographs of microtomed sections of processed emulsions. A covering power limit of 360 for neutral silver was obtained experimentally and verified theoretically. Much higher values were obtained for coloured specimens. Covering power as high as 1850 was measured for silver spheres suspended in water. Detailed comparison of experimental and theoretical values of absorption for silver spheres showed sufficient discrepancy to require different optical constants for silver in bulk and in small particles. Additional changes in the optical constants of silver particles were observed either by incorporating impurity metals in solid solution or by adsorbing impurities (such as cyanine dyes) to the surface.