How is a photograph created? One may first have to consider how an image is formed. For an image to form, visible light must first travel through the camera lens. Once the light reaches the film that is made out of light sensitive emulsion (a thin layer of gelatin) and a base of transparent cellulose acetate or polyester, an exposure has taken place.1 The film also contains silver halides, chemical compounds of silver with halogens (e.g., silver(I) bromide, AgBr; silver(I) chloride, AgCl; and silver(I) iodide, AgI), within the film emulsion that are typically light sensitive.3 When the film is exposed to light, it undergoes physical change. The change of the halides forms a latent image that can be seen once chemically processed.1 The process of development can be described as taking the latent image and making it visible through a chemical process that reduces the silver halides and converts them into clumped grains of metallic silver.3 A sample reaction is shown in Figure 1 below. Developing the film requires a few components that include time, temperature, chemical choices, and method of agitation
The process of developing photographs is quite intricate. To begin, you must have a dark room. A dark room is a room that is absent of any light, with the exception of proper lighting. Proper lighting would be white light (40-watt bulb) for general illumination, and a safelight for the need to see in the dark that will not affect the film or printing paper.2 It should be noted that both lights would not be on at the same time. Proper lighting is required so that films as well prints are not overexposed to light, which could ruin the product entirely. The room has two sides: a wet for developing the photos, and a dry for drying the photos. Development takes place on the wet side. To properly expose the film, time must be adequately used for the silver halides to properly react and obtain the proper density.2 If a film is developed for too short of an amount of time, the photo would be underdeveloped.3 If left for too long, the film would be overdeveloped and the levels of contrast within the film would be too high.3 There must be a balance between contrast and density.
Temperature of the solution used affects the rate of which the film develops. A high temperature will always yield a faster reaction, which also decreases the time of development. It is important that, when developing the film, all processes from wetting, washing, and drying must be done at the same temperature.2 This is to prevent reticulation from happening. Reticulation is wrinkling of the film caused by temperature change when it is most vulnerable due to the emulsion being soft.2 Optimum temperature of processing is room temperature, about 25°C.4 The temperature does not have to be exact every time, but must at least have a consistency of a two to three degree range.
Chemical choices used in development are important for the reason that different films require different chemicals.3 It is exceedingly important that all chemicals used do not come into contact with one another since each chemical used in development has different properties and purposes. The film is first processed in a chemical agent called developer. Developer is comprised of more than one developing agent and there are different types of developers depending on whether or not the films being printed are for black and white prints or color prints.3 Example of chemicals contained within a black and white developer would include hydroquinone for the contrast of the film, sodium sulfite that prevents oxidation from occurring by exposure to air, an alkali like sodium carbonate to activate the developer, and potassium bromide that prevents the developer from processing any unexposed silver halides as well as converting the exposed silver halides to metallic silver grains.2-3
The method of agitation is also important when wanting to develop film with a sense of efficiency. This means that film must have a consistent exposure to the chemicals used.2 Agitation itself is the movement of films that are relative to the immersing solutions used.2 Like temperature, the method of agitation must be consistent for an even development. If agitation were inadequate, the by-products (bromide for example) would not be evenly distributed causing unevenness for the film.2 By-products are a secondary product that come from a chemical reaction that are not inteionally produced. The by-products also prevent other chemical reactions from happening due to the barrier created between the fresh solution and the emulsion.2 Without proper agitation, the film would be ruined since the process cannot be corrected.
A picture will continue to develop on the film and become overexposed unless it is stopped. That is why a stop bath is required. A stop bath is comprised of acetic acid that chemically neutralizes the developer.2 There are guides that contain specific times required for certain films to develop. Some films do not require acetic acid to stop development, and washing off the developer with water sufficiently would also work.2 The next step of development would be to fix the film through a process called “fixer.” Chemicals commonly used for fixing includes ammonium thiosulfate (NH4S2O3) and sodium thiosulfate (Na2S2O3).1 Fixing the film removes the silver halides that were not exposed to light and did not develop from the emulsion, as well as prevent the film from reacting to anymore light.1 This causes the image to be permanent on the film. The final step would be to wash the film of all processing chemicals with running water.1 Once the film is fully developed after drying, it can then be enlarged and printed for photographs of desired size.
- Funk & Wagnalls New World Encyclopedia. Photography; World Book, Inc.: Chicago, 2016. p 1.
- Baker, A. Photography: Art and Technique; W.H. Freeman and Company: San Francisco, 1985. p. 229-251.
- Rogers, D. The Chemistry of Photography:From Classical to Digital Technologies; The Royal Society of Chemistry: Cambridge, 2007. p 25-65.
- The Editors of Time-Life Books. The Print - Life Library of Photography; Time-Life Inc.: New York, 1981. p 54-78.