Processing the Print

When the image has been exposed onto the light sensitive paper using the enlarger for the appropriate aperture and time duration, the paper then has to undergo a developing process in order for the image to become visible. The process steps and chemicals are as follows:

Developer:

In this stage, a chemical mixture is applied to react with the exposed silver halide crystals in the emulsion on the paper. The primary component of this chemical is the developing (or reducing) agent which commonly can be hydroquinone, Metol or phenidone. The differing agents will produce varying results in regards to the film or print contrast, graininess and colour.

In addition to the developer, there is also an alkali accelerator present in the chemical mixture such as sodium hydroxide, sodium carbonate or sodium sulphite which quickens developing time and produces higher contrast. It may also lead to excessive fog, soft emulsions, coarse grain and shorter developer life.

To reduce the potential for chemical fog, which is the development of unexposed silver halide crystals, a restrainer such as potassium bromide or benzotriazole is used. This chemical slows the developing action in areas of the emulsion that have undergone less exposure.

To minimise the oxidation of the developer chemical mixture, sodium sulphite is often used as a preservative.

Stop Bath:

Following the developer step, a weak acid rinse, usually an acetic acid solution, is applied to stop the developing action. This is more commonly known as the stop bath. Water can be used as an alternative but it is not able to halt the developing action and results in shortening the life of the fixer.

Fixer:

The fixer dissolves the undeveloped silver halide crystals from the film or paper emulsion. If a print is fixed poorly, then it will become stained with the darkening of the remaining silver halides.

Generally, sodium thiosulphate or ammonium thiosulphate is used as a fixing agent. The fixer mixture also contains a weak acid (acetic acid) to stop the developing action. The disintegration of the fixer is prevented by the presence of a preservative.

If the fixer is being used for film processing then the mixture will contain two extra components. These are a hardener to protect the emulsion from softening or getting scratched and a buffer to maintain the acidity of the fixer when a hardener is used.

Water Wash:

Immediately following the fixer the paper emulsion must be rinsed in running water to thoroughly remove any remnants of the chemicals.

 
Steps of the Process:

The paper with the exposed emulsion will be placed in sequential baths of developer, stop bath and fixer to then be rinsed by running water. Depending on the chemicals used the durations in each of the baths will vary, an example for resin coated paper would be:

Developer – 2 minutes in Ilford Mulitgrade paper developer (diluted 1 part to 9 parts water at 20°C)
Stop bath – 15 seconds in acetic acid solution (diluted 1 part to 19 parts water)
Fixer – 2 minutes in fixer solution (diluted 1 part to 4 parts of water)
Water Wash – 15 minutes

Important features during processing

Temperature:

The temperature of the chemicals during processing is critical for film processing as it determines the rate at which the film develops. Generally the ideal temperature for developing is 20°C (68°F) and therefore the duration of development must be adjusted if there is a variation in temperature from 20°C. The following chart illustrates how the development time must be altered depending on the temperature of the chemical solutions. It can be used for different manufacturer’s chemicals.

If development time and temperature do not correspond, then the film density will change:

·    Over-development: The highlights or the dense areas of the negative will become too dense which could lead to the loss of the highlight detail and increase contrast.
·    Under-development: This results in a thin negative with low contrast and has the potential for loss of detail.

Agitation:

This is an important feature during film and print processing as continuous or intermittent agitation ensures that the emulsion surface comes into contact with fresh solution. Even development of the film or print is ensured by agitation and it can have a significant impact on the contrast of the images.

Washing:

Washing is an important step to ensure that all residual fixer is removed from the film or print following processing. This is beneficial for the film or print in the long term, as it will prevent the image darkening over time.

Washing aids can help to remove fixer and can also reduce washing times. An example of a washing aid is Kodak Hypo Clearing agent.