Miscellaneous Optical Effects, Color, Photography

The colors of precious opal has already been discussed in connection with ordered aggregation and the interference colors of uniform layers of particles described under adsorption of particles on surfaces. 

Numerous patents have been issued on antireflection coatings in which silica in various forms is deposited as a thin, adherent layer, generally on the surface of glass or plastic sheets and lenses. Coating with a low-hydrated oxide of silica was described in 1945 (698). Films of colloidal silica are deposited in various way (699-704). 

Photographic and diazo-type papers are coated with colloidal silica (720-723). In Polaroid photographic Film colloidal silica plays an essential role in the receiving layer to which the image is transferred and in which the black silver positive image is 

Other uses in photography involve silica-hardened gelatin surfaces on X-ray film (726), colloidal silica-modified silver halide emulsions for higher sensitivity (727), and silica-polyvinyl alcohol as a replacement for gelatin in image-receiving layers (728). 

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