Developer constituents

The developers are chemical solutions, sometimes simple, sometimes rather more complex. The four most important chemical constituents in a developer for black-and-white films have accepted labels, apart from their chemical names. The Developing agent should be the preferred term because there are innumerable reducing agents (chemical solutions that can reduce silver halides to metallic silver). The requirement for a developing agent, however, is that it shall reduce light-struck grains much more rapidly than those that have received no light, preservative, accelerator and restrainer. All developers must also contain a solvent and that is almost universally water. So given proportions of four readily-obtainable chemicals dissolved in water can form a developer. In practice, the solution is more likely to contain five chemicals because as we shall see, metal and Phenidone work best in conjunction with hydroquinone. The Metal and Phenidone work in similar ways. They produce an initial density rapidly but do not build to a high density. It is used as the only developing agent they produce soft but fully detailed images. The hydroquinone is used as the only developing agent has the opposite tendencies. It is slow starting but eventually builds to a high density in highlight areas. The image is generally too contra sty for normal use. Used together in suitable proportions, however, metal and hydroquinone, or Phenidone and hydro quinine bring the best out of each other to form fully detailed negatives of adequate density in a reasonable time.