About Chemistry in Photography

By Nicole Harms
About Chemistry in Photography

Many people think film photography is simple. You load the film into the camera, point and shoot, right? While the process of taking a picture may seem simple on the outside, inside the camera and photo lab a complex chemical process is taking place. Learning more about this process will help you understand just how special taking a photograph is.


In 1825, Joseph Nicephore Niepce took the first permanent photograph. The image was captured on a pewter plate covered with bitumen of Judea, a chemical derived from petroleum. In 1839, Niepce's associate, Louis Daguerre, invented the daguerreotype, a photograph taken using a silver-coated copper plate. Silver chloride and negative images were introduced by Fox Talbot in 1840. George Eastman tweaked the process further, and his ideas are still used in today's film cameras. In 1884, Eastman perfected a gel- and paper-based film, eliminating the need for plates and chemical bottles and allowing the common person to take photographs.


Film is coated in special chemicals known as photographic detectors. These chemicals are changed when put in contact with light energy. The main photographic chemical used in today's film is silver halide. When exposed to light, the chemical destabilizes in accordance to the wavelength of the light and forms a latent image of what is being photographed. In color film, there are three layers of the silver halide that are specifically formulated to be sensitive to red, green and blue light.


In color film developing, reducing chemicals develop the exposed grains of silver halide to create pure silver. This creates an oxidized developer, which reacts with the image-forming layers of the film to create color. Once complete, a stop bath stops the action of the developer. Then, with the silver removed from the film with a fixing solution, the negative is washed and dried. This creates a negative image, or one that is opposite in color, to the true image that was photographed. Because the silver halide is now gone, the film is no longer light sensitive. The process must take place in a dark environment, however, or the film will be exposed and the images ruined.


Chemistry is also involved in making prints. Photographic paper is coated with silver halide grains on the image-producing side. For color prints, these grains are sensitized to blue, green and red lights. The image is projected through the negative onto the paper, which forms a latent image in the silver halide grains. The paper is then sent through an oxidized developer, which creates both a silver image and a dye image. The paper is washed, and then the silver image and any unused silver halide are removed in a bleach-plus-fix solution. The paper is washed again, and then dried, resulting in a color photograph.


Black and white photographic chemistry works in a similar manner. However, the silver halide grains in black and white film are not sensitized to specific colors. The images are captured and the prints are developed in a similar fashion. Because there is no color adjustment needed in black and white photography, many photographers choose to develop these prints in their own dark rooms. This allows them to have control over the length of time that the paper is exposed to the light, thus increasing or decreasing the amount of contrast in the resulting image.


Many digital photographers think that printing their images at home is the same as taking the memory card to the photo lab and having prints made. Because of the chemical process involved in making prints at the lab, these prints are much more permanent than any that are printed on a home printer. The chemical process binds the image to the paper, unlike printing an image using only printer ink. Digital photography skips the chemical process of binding the image to the film, but chemistry is still involved in making a quality digital print.

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