DARKROOM TECHNIQUES

LEARNING OBJECTIVE: Recognize the basic techniques used in a darkroon in terms of using solutions and equipment.

After apiece of photographic film or paper has been exposed to light, it is necessary to process the image and change it from a latent to a visible and permanent image. The process is chemical, and although you do not need to understand why the chemicals act as they do, it is important to know which chemicals/solutions are used, the order in which they are used, the recommended temperature and the required time.

"Photographic processing" can be defined simply as a series of chemical changes that accomplish the following goals:

l Develop the image

l Stop the action of development at a desired point

l Fix the visible image to make it permanent

l Wash away all traces of chemicals used

l Dry the photographic material

PHOTOGRAPHIC SOLUTIONS

In the most basic processing, only two solutions are required: a developer and a fixer, plus water for washing. Additional solutions can be used as film conditioners to shorten processing time or to preserve other solutions. The solutions commonly found in military imaging facilities, craft shops and even home labs are as follows: 

l Developer 

l Stop bath 

l Fixer 

. Wash 

l Wetting agent

Developer

When a photographic emulsion is exposed to light, the silver halides (usually silver bromide and/or silver chloride) in the emulsion change chemically. However, no noticeable change can be seen until the film is developed. The developer causes the affected silver halides to change into metallic silver while having no effect on the unexposed silver halides. The result is that a subject area reflecting the most light will affect the most silver halides and will be the darkest part of the image formed in development. That which is light in the subject is dark in the processed image and inversely, that which is dark in the subject is light in the image.

There are many types and brands of film and developer that all do the job they are designed to do. Reading and following the manufacturer's directions is the soundest advice that can be given. If the manufacturer states that a developer is for general use with film, do not expect good results trying to use it to develop prints. If the manufacturer states that the proper time to develop a certain film is 10 minutes at 70 degrees Fahrenheit (F), do not expect good results at five minutes or at 50 degrees F. If the manufacturer advises thoroughly dissolving Part "A" before adding Part "B," mix the developer that way or be prepared to get inferior results.

Stop Bath

It has become common practice to rinse film in running water after development to retard development and to remove excess chemicals. With prints, it is equally common to use an acid bath to stop the action of the developer and prolong the life of the fixer. In either case, the bath is referred to as a stop bath. Acetic acid diluted with water is the most commonly used stop bath.

Fixer

The fixer is sometimes called "hype" because the main ingredient of the fixer formula, sodium thiosulfate, is also known as hyposulfate.

Figure 11-25. - Roll film processing tank and red.

The purpose of the fixer is to convert the silver halides not changed to metallic silver in the developer into a soluble form. These soluble salts diffuse out of the emulsion and into the fixer. Navy imaging facilities use a recovery system to reclaim silver from chemically exhausted fixer.

Most fixer formulas include chemicals to harden the emulsion, which is greatly softened by the alkaline developer, and minimize scratching in later processing and handling. There are many types of fixers and many brands, as is the case with developers. All do their intended job if the manufacturer's directions are followed.

Wash

Running water is not actually required but greatly simplifies the removal of all the chemicals previously used. The wash step is necessary if you desire a permanent image without stains. Wash films and papers with fresh running water for about five minutes.

Wetting Agent

The wetting agent, usually called Photo-Flo, is a chemical designed to reduce the surface tension of water, thus reducing the possibility of water spots forming on film as it dries. It reduces the overall drying time of your films and prints - a point to consider especially on "rush jobs."

DARKROOM EQUIPMENT

The equipment required to process film can be minimal: a processing tank, graduate (measuring cup) and thermometer. During processing, the film must be kept in total darkness until the image is fixed. Although there are other methods for accomplishing this, the simplest method is to use a lighttight stainless steel tank designed for the type and size of film being processed.