Developer liquid

The developer liquid (also developers called) in analogue photography the task of the latent images of exposed film to visualize (see photo emulsion ).

Developers are reducing agents to which exposed and unexposed silver halide crystals react differently. During the development process, the developer is oxidized , that is, it releases electrons which are absorbed by the silver ions. These then become metallic, i.e. visible, silver.

This reaction mainly takes place where light has fallen on a silver halide crystal and traces of metallic silver have emerged as a result (latent image). This metallic silver acts as a catalyst for the chemical reduction of the silver ions during development.

During the subsequent fixation , the superfluous residues are washed out.

In color films , color couplers bind to the silver during development, which is then removed from the emulsion by the bleach bath , so that only the dyes are contained in the film.

Black and white developer

Various chemicals are used as developer substances, the choice of which influences the result, especially with black and white films. Frequently used reducing agents are p- aminophenol , which is sold by Agfa as Rodinal , hydroquinone , which is contained in Neofin from the manufacturer Tetenal and Kodak's TMax, and p-methylaminophenol sulfate , which is also contained in Neofin and Ultrafin . Virtually all black and white developers contain these or combinations of these reducing agents. In addition, the developers often contain preservatives as well as acids and bases to regulate the pH value . Alternative developers such as Caffenol , on the other hand, consist of environmentally friendly substances that are available in every supermarket. The same substances in different concentrations are usually used to develop black and white papers.

Color developer

Color developers are very complicated formulas. The development process C-41 is used almost exclusively for today's negative color films, the process E-6 for slide films and the development process RA-4 for color papers .

Holography developer

In the holography different developers are used which have different compositions depending on the type of the recording material and the type of hologram. Many of these developers are based on pyrogallol , metol , or urea . Additives include sodium sulfite or sodium carbonate . In some cases, standard photo developers are used that are easy to use, but in many cases do not lead to optimal results.