The world’s first photoetching was produced in France in 1822. For more than half a century, scientists conducted extensive research on the physical properties of light and chemical elements, as well as optics and technology. They were looking for a way to transfer the image visible to the eye onto some surface.
Research and experimentation resulted in the invention of the photo camera and later the film. At first, photography was only accessible to professionals, but with the advent of portable cameras and roll film instead of photographic plates, it became an affordable hobby. A number of chemical solutions were used for photographic development, most importantly, a fixer, a stop bath, and a developer.
Developers are classified into several groups, including one-solution, two-solution, concentrated, tablet, and paste-like types. One-solution developers contain all substances in a single solution, whereas two-solution developers contain the developing and accelerating agents in two solutions, which are stored separately. They are mixed in the necessary ratio before use, forming a developer. Less frequently, the photographic material is treated successively using two types of solutions.
Concentrated developers contain the same substances as one-solution ones, but with a concentration that is 10 to 15 times higher. As a result, they can be stored for up to one year. Before use, a concentrated developer is diluted with water to achieve the standard concentration.
Paste-like developers are convenient for use in portable development equipment. They are applied in thin layers on the emulsion using special applicators and then washed off.
The main components of modern developers are organic, benzene-based developing agents. Their concentration can vary depending on the purpose. Solutions containing two developing agents instead of one are also widely spread.
They function according to the principle of superadditivity where the rate of development of the two agents is significantly greater than the sum of the rate of each agent used alone.
