Anti-halation backing

An anti-halation backing is a layer found in most photographic films. It is usually a coating on the back of the film base, but sometimes it is incorporated between the light-sensitive emulsion and the base. The light that passes through the emulsion is absorbed by the anti-halation layer. This prevents any light from being reflected back through the emulsion from the rear surface of the base, or from anything behind the film, and causing a halo-like effect around bright points or edges in the image. The anti-halation layer is rendered transparent or washed out (as in K-14 films) during processing of the film.

The lack of an anti-halation layer in Kodak's High Speed Infrared film (HIE) (HIE) is the cause of the ethereal "glowing" effect often associated with infrared photography, rather than an artifact of IR itself.