Q: What type of gelatin is used in the manufacture of photographic film? Is synthetic gelatin used?
A: Gelatin is critical to photography, as we know it. Before gelatin came into use, photography was very difficult, time-consuming, and expensive because of the processes that had to be used. However, once gelatin became the medium in which the silver halide crystals were precipitated and the medium coated onto the glass or plastic support, photography became practical for use by the public. Gelatin, a naturally occurring polymer, is a long chain composed of a number of different amino acids. These chains interact with the silver ion and the silver halide crystal during crystal formation and growth so that the silver halide grains grow as individual grains and do not clump together. During the coating operation, the gelatin solution with the silver halide grains and any other photographic chemicals is gently warmed at which point it has a low viscosity and flows quite freely. However, immediately after coating, the material is cooled, actually only a modest drop in temperature, and the solution “gels” or forms a layer that does not flow. This allows the coating of photographic products at relatively high speed and the coating of many different layers on top of each other without mixing during the coating operation. At the time of coating hardeners are added to the solution so that after the coating step, the layers will become hard enough that they will not dissolve during the processing of the exposed film. Gelatin also has the property that the hardened gelatin layers will swell when wet and allow the processing chemicals into the layers so that the development reactions can occur, but the layer structure remains intact. Because no other synthetic materials have been found that have all of these properties, gelatin has been used in the production of photographic products for over 100 years.
The gelatin used in photographic products comes from the bones and hides of pigs and cattle. Gelatin is manufactured from the protein collagen. The exact manufacturing process used depends on the properties the gelatin needs to have. The hides or bones are soaked in an acidic or basic aqueous solution for a period of time ranging from hours to months followed by a gradual increase in temperature to extract the gelatin. The gelatin solution is then drained and washed. After the pH is adjusted, the gelatin is filtered, clarified, concentrated, and dried. In some cases the gelatin is chemically treated some more. The gelatin used by Eastman Kodak in its photographic products comes from a subsidiary company, Eastman Gelatine Company (www.eastmangelatine.com). Eastman Gelatine produces gelatin for the imaging, pharmaceutical, and food industries. The gelatin produced for the imaging industry is the highest purity gelatin produced because of the sensitivity of the silver halide crystals to any chemical impurities.