Developing film is a chemical process in which the exposed silver halide in a piece of used film is washed and fixed. This creates the permanent image known as a negative, which is no longer sensitive to light. The process of developing film involves several chemicals, some of which can be toxic or dangerous. As the chemicals used in developing film are commercially available, film developing can be done at home but should always be undertaken in a well-ventilated area.
Developer
Developer is the first stage in fixing an image on a negative, revealing the latent image by washing away some of the exposed silver halide crystals. It is made of a diethanolamine-sulfur dioxide complex, hydroquinone, sodium bisulfite, and potassium bromide mixed with water. The longer a negative is left in the developer, the more silver halide is removed, resulting in greater contrast. The art of leaving a film to develop longer than the recommended time is known as "pushing" the film, as it leaves the chemicals in contact with the film longer. Pushing the film can be done to correct underexposure, but will make the grain of the film more visible.
Stop Bath
Stop bath halts the action of the developer on the negative by changing the pH balance, neutralizing the chemical reaction. It is usually a form of acetic acid mixed with water. This dilute concentration gives off a characteristic vinegar smell. It is sold as a concentrate and then mixed with water by the user. Caution should be undertaken when working with acetic acid stop bath, as contact of the concentrated form with unprotected skin can cause chemical burns.
Water
One of the most important and readily available chemicals used in film developing is water. The film is rinsed between stages in a bath of water to remove chemicals, it is also rinsed at the end of the process in order to prepare the film for drying. As most of the chemicals are sold as concentrates, they must be mixed with distilled or purified water in order to be used. A steady supply of running water is necessary for any darkroom activity.
Fixer
The semi-final stage of film development is the fixer. This removes the unexposed silver halide and leaves behind the developed, exposed silver halide. Fixer consists of a salt of sodium thiosulfate mixed with water. The process of fixing ensures that the image on the negative is no longer sensitive to light, or "fixed". This is followed by a final water bath in which the film is rinsed, then hung to dry in a dust-free drying cabinet.
Considerations
Working with darkroom chemicals can be dangerous. Having the Material Safety Data Sheets (MSDS) for any chemicals being used is recommended and in some cases required by law, as these sheets detail the chemical content, hazard, and treatment for contact or ingestion. The chemical fumes can be quite dangerous, so ventilation is an important consideration in any darkroom application. Handling the solutions should always be done with care and adherence to safe chemical handling procedures. Protective clothing such as gloves and goggles can be used to prevent undue contact with chemicals while developing film.
Tags: mixed with, silver halide, mixed with water, with water, exposed silver