Difference Between Developing And Printing
When a photograph is taken, a latent image is formed consisting of specks of metallic silver in the light-sensitive emulsion of the film. The latent image cannot be seen until it is transformed into a visible image as a result of the chemical process called developing. The chemical reactions of developing will produce varying results depending on the temperature at which they take place and on how long they are permitted to continue. It is important to follow the instructions supplied with all photographic chemicals regarding temperature and time in order to achieve the best possible results.
To develop black-and-white film, the film is removed from the camera in total darkness and loaded into a developing tank. When the light-tight cover of the tank is securely in place, the rest of the procedure can be carried out in normal light.
First, developer at the proper temperature is added to the tank through the light-tight opening in the cover. The developer is left in the tank for the recommended period of time and the tank is agitated during this time to keep the developer moving over the surface of the film. When the recommended time has elapsed, the developer is poured from the tank through the cover opening. Water, or a stop bath of water plus a small amount of acetic acid, is poured into the tank and agitated. This step stops the developing reaction and removes developer from the film. The water or stop bath is then poured from the tank. A fixer solution, commonly called hypo, at the proper temperature is poured into the tank, agitated, and allowed to remain for the recommended time. The fixer removes the sodium halide crystals that were not converted to metallic silver by exposure to light. The fixer is then poured from the tank. Now the development and fixing is complete, and the tank may be opened. The film must be washed for about 30 minutes and allowed to dry.
The print is made by passing light through a negative onto a sheet of printing paper. Such paper is coated with a gelatin that contains light-sensitive silver salts, similar to those used for negatives, but less sensitive.
If a print is the same size as the negative, it is called a contact print. The printing paper is pressed tightly against the negative in a glass frame. After being exposed to the light of an electric bulb for a few seconds, it is later developed, rinsed, fixed, and washed. This process is performed using a series of trays under a yellow “safelight,” which does not harm the emulsion.
Prints larger than the size of the emulsion are made by projection. They are enlarged by an enlarger, a device that works like a turned-around camera. Strong light is thrown on the negative, and a lens projects the negative image to any desired size on the printing paper. It is then processed in the same way as a contact print.