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8.1 - Chemicals
When a photographic emulsion is exposed to light with a camera, printer or enlarger, there is produced an invisible image in the minute crystals of silver halide which is called a latent image. To obtain a visible image, the exposed emulsion is treated in a solution known as a developer. This solution changes (reduces) the light affected halides to black metallic silver. These black metallic silver particles form the visible image.
The Basic Developer
There are many different formulas used for developing solutions, but most all modern developers contain; the following five essential ingredients: (1) solvent or water (2) developing agent; (3) preservative; (4) accelerator or activator; and (5) restrainer.
Solvent or Water - Water is the carrying agent for all of the other parts. All of the ingredients are dissolved in water. Water also serves as a vehicle to carry the developing ingredients to the silver crystals. It also causes the emulsion to swell like a sponge to aid in developing.
Developing Agents - The developing agent is the most important chemical in a developing solution. All of the other ingredients are necessary to make the solution function properly however it is the developer agent that brings out the latent image.
Hydroquinone is a developing agent of low potential. It requires little or no restrainer at normal temperatures of 68 to 72 degrees. Its activity is greatly reduced by low temperatures because it becomes inert at about 50 degrees. At a temperature of about 80 degrees it works so energetically that it will develop the unexposed parts of an emulsion. This produces chemical fog.
Hydroquinone is capable of producing highlights of great density while keeping transparency in the unexposed areas. It works first on the areas of greatest exposure, the highlights. The areas of least exposure, the shadows, will be the last to be developed. It is an ideal developing agent for subjects requiring extreme contrast. It builds contrast first and density afterward.
Metol and Elon are trade names for other good developing agents. Metol alone or in combination with hydroquinone has been one of the most popular developing agents since prior to 1900. Metol will complete the development of the least exposed areas soon after development starts. The areas of greatest exposure will be the last to be completely developed.
Metol combined with hydroquinone (M-Q) is a very popular developer. The soft working Metol and the high contrast Hydroquinone make a superior combination. M-Q developer keeps well in solution, does not stain, and is faster working than either one of the agents used separately.
The Preservative - All developing agents being alkaline will oxidize very rapidly. It is necessary to add a preservative to prevent excess oxidation. The preservative prolongs the life of the developing solution and prevents the formation of colored oxidation products, which cause stains.
The preservative has a great affinity for free oxygen, and will combine with it when mixed into a solution. A large amount of free oxygen is in the air and in the water used for the solutions. If this free oxygen is left in the water, it will oxidize most of the developing agent and produce stains before the metallic silver image is developed.
Sodium sulfite is the preservative most commonly used. It also dissolves silver halides to some extent and reduces gain size. This makes it very useful in fine grain developers. Sodium bisulfate is also used as a preservative.
Accelerators - All developing agents are either neutral or slightly acid and have little ability to develop on their own. In order to use the capabilities of these agents it is necessary that they be in an alkaline state. To make the developing solution alkaline an accelerator is needed.
The purpose of the accelerator is to hasten the swelling of the gelatin in the emulsion, permitting the solution to penetrate the entire emulsion more quickly, there by speeding the developing time. Accelerators are divided into three general groups: mild, moderate, and strong.
Borax is a mild alkali and is used in low contrast developers for fine grain development. Sodium hydroxide is a caustic alkali. It is used in some developers to produce high contrast. Caustic alkalis are avoided for fine grain development because they soften and swell the gelatin excessively, which permits the formation of larger developer silver grains in the emulsion.
A deficiency of alkali slows development. An excess of alkali increases the contrast and activity of a developer but may be overdone which will cause an over swelling of the gelatin, which may produce blisters. The more active the developer, the greater the clumping action of the silver grain. Because of this the milder or less alkaline developers yield finer grain.
Restrainer - A restrainer prevents the developing solution from working too rapidly. This will cause the unexposed silver halides to be developed which produces chemical fog, development streaks and an image lacking in contrast. When a restrainer is added, the development time is lengthened and fog minimized. Contrast is increased because the developing agent's activity is cut down in unexposed areas. The restrainer acts as a brake on the combined action of the developing agent and accelerator. Potassium bromide is used as a restrainer.
8.2 – Stop Bath
When a negative or print is removed from the developing solution, there is a small amount of developer both in the emulsion and on the surface which must be removed to stop the action of the developer and to prevent stains. To remove the developer from the print or negative it should be immersed in a rinse bath of which there are three general types: Water, acid, and hardening.
A water rinse bath helps retard the action of the developing agents and remove excess developer from the emulsion, thus preventing contamination of the fixing bath. It is suitable and sufficient for most negatives.
An acid rinse bath, sometimes referred to as stop bath, instantly neutralizes the action of the developer. It also neutralizes the alkalinity of the developer and prolongs the life of the fixing bath. Acetic acid (28%) is used for the acid rinse.
A hardening rinse bath is used to harden the emulsion when processing at high temperatures. In ordinary processing, the hardening agent in the fixing bath is sufficient, thus permitting the use of water or acid for a rinse. Potassium chrome alum is the chemical used for hardening but is very unstable as it exhausts very rapidly. There is an indicator stop baths that turn color when exhausted.
Dilution of Glacial Acetic and other Acids
To make a 28% solution of acetic acid from glacial acetic acid, dilute 3 parts of glacial acetic acid with 8 parts of water. To make a gallon of stop bath the 28% solution must be diluted as follows: 6 oz's of the 28% solution to 122 oz's of water. When diluting concentrated acids, use caution to avoid contact with the skin and always add the acid to the water slowly, stirring constantly. Never add the water to the acid because the solution may boil and spatter the acid on the hands or face causing serious burns.
Fixing Bath
The fixing bath is used to dissolve the unexposed silver salts from the emulsion. Making them soluble in the fixing solution does this. If the fixing solution has been used a lot and contains a high silver content, the developer can react with the fixer and cause the silver to precipitate on the film which is called diachronic fog.
The fixing bath contains six basic ingredients which are: (1) The solvent or water, (2) the fixing agent, (3) the preservative, (4) the neutralizer or acidifier, (5) the buffer, and (6) the hardening agent.
The Solvent - The solvent or water or vehicle (what ever its called) not only dissolves the other ingredients but also carries them into the emulsion.
The Fixing Agent - All fixing baths must contain a silver halide solvent. This solvent is known as a fixer. This fixer agent dissolves silver chloride, silver bromide, and silver iodide. The universal fixer agent used in photography is sodium thiosulfate. This is commonly called hypo, which is taken from its other chemical name hyposulfite.
The Preservative - Sodium sulfite is used as the preservative in the fixing bath. The Preservative prevents the fixer from decomposing or oxidation. Strong acids tend to cause a fixing agent to sulfurize. The sodium sulfite acts as a preservative by combining with the sulfur and actually forming new hypo.
The Neutralizer - Acetic acid is used to further neutralize any developer carried over from the rinse bath or stop bath. This prevents staining. It simply stops the action of the developer remaining in the emulsion.
The Buffer – The buffer is used so that alkaline developer can be added to the fix (by carryover) without significantly changing the acidity.
The Hardener - The emulsion is very soft due to the swelling of the gelatin during development. A hardener is added to the fixer to prevent frilling, reticulation, scratches and other undesirable effects. Its use is simply to harden the gelatin to prevent further swelling. Potassium chrome alum is used for this.
Hypo Eliminator
Hypo eliminator is used to remove fixer from the emulsion with no emulsion swelling or softening therefore shortening the washing time. Eliminator will shorten the washing time. This chemical is as critical when using RC paper.
Wash
Wash is a solvent used to clean the emulsion so that it is free from chemicals. The wash cleans the print.
Post Wash Aids
Photo-flo solution decreases water surface tension and minimizes watermarks and drying streaks on film and speeds drying.
8.3 - Popular Developers
Every developer is made to perform a specific function, each has its own special properties. They are designed by the photographer to do a specific task. Since all developers contain the same basic ingredients, the amount of each will effect the development time, temperature, contrast, activity, and grain. The following developers are only a few of the more commonly used and manufactured by companies.
Acufine: Powerful but moderately soft-working formula providing outstanding general-purpose combination very high film speed (about one full stop extra speed as compared to film maker's recommended development with most popular films), excellent sharpness, medium fine to fine grain, moderate contrast. Easily contaminated in use otherwise, keeps fairly well.
AGFA Rodinal: Powerful liquid concentrate, used as a single-shot at extreme dilution. No fine-grain formula, but graininess pattern is tight, razor edged. Excellent image sharpness. Concentrate keeps very well, in small, air-free bottles. Avoid skin contact with concentrate.
Diafine: Two solutions, used in succession. Time in each solution is same for all films (2-3 min. for 35mm; 3-4 min. for roll). Usable over wide range of temperatures. With some films outstanding; gives speed increase (about one stop compared to film maker's recommended development) with moderate contrast, excellent sharpness, medium fine to fine grain. With other films speed gain (if any) may be minor with much higher contrast. Agitation has important effect on results; follow directions carefully. For best results, mix with distilled water; use separate tanks for each solution, develop in total darkness, transferring reels from tank to tank. Easily contaminated in use, so cleanliness and care are important; otherwise, keeps well and has long use life.
Kodak D-76: Outstanding versatile, powerful, soft-working formula. High film speed, moderate contrast, fine-to medium-fine grain, excellent sharpness. Diluted 1 to 1 make it a good single shot developer. Very long life (undiluted) in use and storage.
Kodak DK-50: Two energetic non-fine-grain types which, diluted, make soft-working single-shots. Medium to high film speed, good sharpness, moderate contrast. In general, Isodol develops negatives to a slightly higher contrast than DK-50 will in the same time. Use Isodol for Ansco films, DK-50 for Kodak films. DK-50 is useful and inexpensive to develop large film sizes and great quantities of films.
Kodak HC-ll0: Highly concentrated formula, dilute to make a powerful, active solution. Useful for handling large numbers of roll and sheet films quickly. HC-110 offers good sharpness, high film speed, medium fine grain, and moderate contrast. One bottle of concentrate makes 2 gallons of 1 to 15 working solution, 4 gallons of 1 to 31. Although listed here as single shot it can be replenished and has very long use life.
Kodak Microdol-X: Very fine grain, soft-working, moderate film speed, and good sharpness. Use and storage life somewhat less than for D-76. Diluted 1 to 3, there is a small but noticeable increase in film speed, slightly more graininess.
Kodak Dektol Developer: For neutral and cold-tone images on coldtone papers. Some examples of different papers are: Kodabromide, Kodak Medalist, Velox, Azo, Resisto, Poltcontrast, And Panalure. High capacity, uniforms development rate, and long listing. Dektol is used by diluting the stock solution 1part developer to 2 parts water.