Warm:  Reddish colors that by association with common objects (fire, sun, and so on) give an impression of warmth.

Washing aid:  A chemical solution used between fixing and washing film or paper.  It shortens the washing time by converting residues from the fixer into forms more easily dissolved by water.  Also called hypo-neutralizing (or clearing) agent.

Wet-plate process:  A photographic process in which a glass or metal plate was coated with a collodion mixture, then sensitized with silver nitrate, exposed, and developed while the collodion was still wet.  It was popular from the 1850s until the introduction of the gelatin dry plate in the 1880s.

Wetting agent:  A chemical solution used after washing film.  By reducing the surface tension of the water remaining on the film, it speeds drying and prevents water spots.

White light:  A mixture of all wavelengths of the visible spectrum.  The human eye sees the mixture as light that is colorless or white.

Wide-angle lens:  See short lens.

Working solution:  A chemical solution diluted to the correct strength for use.