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C 41 black and white film11/20/2023 ![]() This also explains why ascorbate developers have poor keeping properties, as oxidised ascorbate is both ineffective as a developing agent and lowers the pH of the solution, making the remaining developing agents less active. ![]() Ascorbate developers may have the advantage of being compensating and sharpness-enhancing, as oxidation by-products formed during development are acidic, meaning they retard development in and adjacent to areas of high activity. This, however, suffers from poor stability. Hydroquinone can also be toxic to the human operator as well as environment some modern developers replace it with ascorbic acid, or vitamin C. Some photographers add a pinch 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.īecause metol is relatively toxic and can cause skin sensitisation, modern commercial developers often use phenidone or dimezone S (4-hydroxymethyl-4-methyl-1-phenyl-3-pyrazolidone) instead. It is important to dissolve chemicals in the order in which they are listed. Metol is difficult to dissolve in solutions of high salt content and instructions for mixing developer formulae therefore almost always list metol first. 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 push the pH up to around pH 11 to 12. Most developers also contain small amounts of potassium bromide to modify and restrain the action of the developer :218-219 to suppress chemical fogging. The original lithographic developer contained formaldehyde (often added as paraformaldehyde powder) in a low sulfite/bisulfite solution. ![]() 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. 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. Notable standard formulas include Eastman Kodak D-76 film developer, D-72 print developer, and D-96 motion picture negative developer.
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