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Photographic developer
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Photographic developer
In the processing of photographic films, plates or papers, a developer is a chemical solution that converts the latent image to a visible image. In the gelatin silver process, the developer achieves this conversion by reducing the silver halides, which are pale-colored, into silver metal, which is black when in the form of fine particles.
Although the developer will react with all grains of silver halide, it acts much more quickly on those that have been exposed to light. When left in developer, all the silver halides will eventually be reduced and turn black. Generally, the longer a developer is allowed to work, the darker the image.
The developer typically consists of a mixture of chemical compounds prepared as an aqueous solution. For black-and-white photography, three main components of this mixture are::115
Notable standard formulas include Eastman Kodak D-76 film developer, D-72 print developer, and D-96 motion picture negative developer.
Hydroquinone is superadditive with metol, meaning that it acts to "recharge" the metol after it has been oxidised in the process of reducing silver in the emulsion. Sulfite in a developer not only acts to prevent aerial oxidation of the developing agents in solution, it also facilitates the regeneration of metol by hydroquinone (reducing compensation and adjacency effects) and in high enough concentrations acts as a silver halide solvent.
As well as the developing agent, the activator and the preservative, most developers contain small amounts of potassium bromide to modify and restrain the action of the developer to suppress chemical fogging. Developers for high contrast work have higher concentrations of hydroquinone and lower concentrations of metol and tend to use strong alkalis such as sodium hydroxide to increase the pH up to around 11 to 12.
Developers also contain a water softening agent to prevent calcium scum formation (e.g., EDTA salts, sodium tripolyphosphate, NTA salts, etc.).
Metol is difficult to dissolve in solutions of high salt content and instructions for mixing developer formulae therefore almost always list metol first. It is important to dissolve chemicals in the order in which they are listed. Some photographers add a pinch[quantify] of sodium sulfite before dissolving the metol to prevent oxidation, but large amounts of sulfite in solution will make the metol very slow to dissolve.
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Photographic developer
In the processing of photographic films, plates or papers, a developer is a chemical solution that converts the latent image to a visible image. In the gelatin silver process, the developer achieves this conversion by reducing the silver halides, which are pale-colored, into silver metal, which is black when in the form of fine particles.
Although the developer will react with all grains of silver halide, it acts much more quickly on those that have been exposed to light. When left in developer, all the silver halides will eventually be reduced and turn black. Generally, the longer a developer is allowed to work, the darker the image.
The developer typically consists of a mixture of chemical compounds prepared as an aqueous solution. For black-and-white photography, three main components of this mixture are::115
Notable standard formulas include Eastman Kodak D-76 film developer, D-72 print developer, and D-96 motion picture negative developer.
Hydroquinone is superadditive with metol, meaning that it acts to "recharge" the metol after it has been oxidised in the process of reducing silver in the emulsion. Sulfite in a developer not only acts to prevent aerial oxidation of the developing agents in solution, it also facilitates the regeneration of metol by hydroquinone (reducing compensation and adjacency effects) and in high enough concentrations acts as a silver halide solvent.
As well as the developing agent, the activator and the preservative, most developers contain small amounts of potassium bromide to modify and restrain the action of the developer to suppress chemical fogging. Developers for high contrast work have higher concentrations of hydroquinone and lower concentrations of metol and tend to use strong alkalis such as sodium hydroxide to increase the pH up to around 11 to 12.
Developers also contain a water softening agent to prevent calcium scum formation (e.g., EDTA salts, sodium tripolyphosphate, NTA salts, etc.).
Metol is difficult to dissolve in solutions of high salt content and instructions for mixing developer formulae therefore almost always list metol first. It is important to dissolve chemicals in the order in which they are listed. Some photographers add a pinch[quantify] of sodium sulfite before dissolving the metol to prevent oxidation, but large amounts of sulfite in solution will make the metol very slow to dissolve.
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