For most reagents, the systematic names according to international nomenclature are given below (e.g., potassium dichromate); for some, traditional (sulfuric acid, alum), and for certain complex compounds, trade names have been retained (e.g., As-107). The first name listed on each card is the one used in recipes; for hydrates, the simplest “aqueous” form has been chosen for the sake of standardization. Synonyms under which the reagent may appear in other photography literature are given in parentheses.
Developing agents
Metol (N-methyl-n-aminophenol sulfate): colorless needle-like crystals or flakes; soluble in water (about 5 g per 100 g of water). Store in a tightly closed dark glass container. Toxic.
Hydroquinone (1,4-dihydroxybenzene, H₂Q): a crystalline powder that is highly soluble in water. It functions as a contrast developer, usually in combination with metol or phenidone; it is sensitive to the accumulation of bromides in the developer. Store in a dark container with a tight-fitting lid. Toxic.
Phenidone (1-phenyl-3-pyrazolidone-3, edifone): a white or cream-colored powder, poorly soluble in cold water (dissolves when heated to 70°C), but readily soluble in alkaline solutions, ethanol, and acetone. It is low in toxicity.
Methylphenidone (4-methylphenidone): a light brown powder that is relatively soluble in water. It is low in toxicity.
Amidol (2,4-diaminophenol dihydrochloride): white needle-like crystals that darken during storage; readily soluble in water. Store in a dark, tightly closed container. Toxic.
Pyrocatechin (1,2-dihydroxybenzene, dinol): white crystals, readily soluble in water (about 50 g per 100 g of water). May stain the skin. Store in a tightly sealed, dark container.
Pyrogallol (pyrogallic acid, 1,2,3-trioxybenzene): colorless needle-like crystals, readily soluble in water (about 50 g per 100 g of water). May stain the skin. Store in a dark container.
Para-aminophenol (n-aminophenol hydrochloride; synonyms: “Codelon,” “Rodinal”): white crystals, readily soluble in water (1:3). The base of concentrated Rodinal-type developers. Toxic.
Para-phenylenediamine (1,4-diaminobenzene, diamine-P): a white or gray powder that is soluble in water, but its aqueous solution decomposes rapidly. It is used in “genuine” fine-grain developers. It is toxic; a dihydrochloride form with the same properties is also available.
Ascorbic acid (vitamin C): a white powder that is easily soluble in water. A modern, low-toxicity substitute for hydroquinone in ascorbate developers such as X-TOL and AKFF.
Glycine “Photo” (N-hydroxyphenylaminoacetic acid): a white or slightly colored powder that is poorly soluble in pure water but readily soluble in solutions of sodium sulfite or alkalis. Toxic.
Chlorohydroquinone (Adurol): a colorless powder that is readily soluble in water. It is used in concentrated developers and in developers for photographic paper that produce a brown tone.
Preservatives (antioxidants)
Anhydrous sodium sulfite (Na₂SO₃): a white powder that is highly soluble in water and is a component of virtually all photo developers. Solubility depends heavily on water temperature and is highest at 33.4°C: 125 g/L at 0°C, 160 g/L at 10°C, 207 g/L at 20°C, 261 g/L at 30°C, 280 g/L at 33.4°C, and then decreases—270 g/L at 40°C, 257 g/L at 50°C, 245 g/L at 60°C, 235 g/L at 70°C, 226 g/L at 80°C, 217 g/L at 90°C, and 212 g/L at 100°C.
Potassium metabisulfite (potassium pyrosulfite): a colorless crystalline powder that is readily soluble in water. It is used in developers, stop baths, and fixers as a more acidic substitute for sodium sulfite.
Sodium bisulfite (sodium hydrosulfite): a clear liquid that is miscible with water in any proportion. It is used in stop baths and fixatives.
Sodium metabisulfite (sodium disulfite, sodium pyrosulfite): a white, readily soluble powder. It is used in stop baths and fixatives.
Accelerators (alkalis)
Sodium carbonate (soda ash): a white powder that is easily soluble in water. The anhydrous salt (1 g) can be replaced with the crystallized hydrate (2.7 g) or potassium carbonate (potash) (0.5 g).
Potassium carbonate (potash): a white, hygroscopic powder that is easily soluble in water (about 100 g per 100 g of water).
Sodium tetraborate (borax): a white crystalline powder, soluble in water (about 5 g per 100 g of water). It is used in developers and tanning fixers. It is toxic.
Sodium metaborate (Codalk): a crystalline powder that is soluble in water. It is used in developers as a milder alkaline accelerator.
Sodium hydroxide (caustic soda): white flakes or granules that deliquesce in air; highly soluble in warm water (about 100 g per 100 g of water). At concentrations above 5%, the solution irritates the skin and mucous membranes. It is toxic.
Potassium hydroxide (caustic potash): a white, amorphous substance that dissolves easily in water (about 110 g per 100 g of water), releasing a large amount of heat. It is toxic.
Aqueous ammonia (ammonium hydroxide): a colorless liquid with a pungent odor that is easily soluble in water. It is toxic at concentrations of 10% or higher.
Triethanolamine: a solid (melts at 21.1°C) that is soluble in water. It serves as both an alkaline medium and a solvent in highly concentrated developers such as PC-TEA.
Sodium bicarbonate (baking soda): a white powder that is highly soluble in water (about 8 g per 100 g of water). It is used in developers as a mild accelerator.
Anti-veiling agents
Potassium bromide: a white crystalline powder that is highly soluble in water (about 65 g per 100 g of water). It is the most common antivalent in photo developers.
Sodium bromide: a crystalline powder that is highly soluble in water. It acts in the same way as potassium bromide.
Potassium iodide: white crystals, easily soluble in water (about 145 g per 100 g of water). A more potent antivalent, it is used in combination with benzotriazole.
Benzotriazole: white or slightly yellowish-brown crystalline needles, poorly soluble in water, but highly soluble in methanol and sodium carbonate solutions. A strong anti-valent agent, but in excess it sharply reduces light sensitivity.
5-Nitrobenzimidazole and its salts (nitrate, sulfate): light-colored powders that are soluble in water. They are used in developers as antivalents.
Fixing and tanning agents
Sodium thiosulfate (hyposulfite, antichlor): a white crystalline powder, readily soluble in water (about 70 g per 100 g of water). The basis for most fixatives. The anhydrous salt (1 g) can be replaced with the crystallohydrate (1.57 g).
Ammonium thiosulfate: colorless crystals that are easily soluble in water. It is used in rapid fixatives—it works noticeably faster than the sodium salt.
Sodium thiocyanate / potassium thiocyanate (sodium/potassium rodanite): crystalline powders that are easily soluble in water and deliquescent in air. They are used in developers, fixers, and toning solutions. Toxic.
Potassium aluminum alum (12-hydrate): colorless crystals or white powder, soluble in water (about 6 g per 100 g of water; to speed up dissolution, the water is heated). Used in tanning fixatives and stabilizing baths.
Potassium chromate (12-hydrate): blue-violet crystals, soluble in water. Used in tanning solutions—they produce a stronger tanning effect than potassium aluminum chromate.
Formalin (aqueous solution of formaldehyde, 37–40%): a colorless liquid with a characteristic odor; it is miscible with water in any proportion. It is used in stabilizing and tanning solutions. It is toxic.
Acids and Buffer Additives
Acetic acid (glacial and diluted): a clear liquid with a characteristic odor; it mixes with water in any proportion. It is used in fixatives, stopping baths, and developers. It is toxic when the concentration of the active ingredient in the solution exceeds 80%.
Boric acid: a white crystalline powder that is sparingly soluble in water (the water may be heated to 70°C). It is used in developers, stop baths, and fixing solutions—often as part of a borate buffer, as in DK-76.
Citric acid (hydrate): a white crystalline powder that is highly soluble in water (about 125 g per 100 g of water). It is used in developers, enhancers, stop baths, and fixing solutions.
Sulfuric acid: a colorless, oily liquid that mixes with water in any proportion, releasing heat (the acid is always added to the water, not the other way around). It is used in fixers, developers, and reversal baths. It is toxic.
Auxiliary reagents: water softeners, complexing agents, wetting agents
EDTA and its disodium salt (Trilon B): a white powder; EDTA itself has poor solubility in water, while its disodium salt has good solubility. It is used for water softening and to chelate metals in developers (including the two-solution developers “Leika News” and “Shtikler”) and in bleaching-fixing solutions. It is low in toxicity.
Sodium tripolyphosphate (A-901): a white powder that is highly soluble in water. It is used in developers and other solutions as a water-softening agent—it prevents calcium deposits from forming on the film.
Sodium-potassium hexametaphosphate (Gram's salt): a white, hygroscopic powder that is readily soluble in water. It is used in photo developers, sometimes in combination with other phosphates (under the trade names “Calgo” and “Lokanit”).
OP-7 / OP-10 (surfactants based on polyethylene glycol ethers): viscous liquids that mix with water in any ratio. Used in final rinses and stabilizing solutions—a classic wetting agent prior to film drying.
Beyond Black-and-White Film Processing
The complete list of photochemical reagents is much more extensive and includes toning agents (salts of nickel, uranium, selenium, lead), for image reduction and enhancement (red and yellow bitartrate, ammonium persulfate), for color processing (Kodak SD-1–SD-4 developers, ethylenediamine), and for alternative processes. These chemicals go beyond the scope of black-and-white film development, which is the focus of this handbook, and are not discussed in detail here.