Which chemicals do I need to process X-ray film?
Making-up processing solutions
Nowadays, chemicals are supplied as a liquid concentrate, suitable for the particular
type of film used.
The processing solutions can be prepared either directly in the tanks or in plastic buc-
kets. In the latter case each type of solution must be prepared in a separate bucket,
which is never used for other chemicals.
Developer
Development fog, graininess and contrast are dependent on the type of developer,
which is preferably made up to suit the film used.
If a concentrated manual developer is used, for example G128 made by Agfa, and the
developer tank has a capacity of, say, 25 litres, then all to do is pour 5 litres of the con-
centrated developer into the tank and add 20 litres of water (ratio 1 part of concentra-
te to 4 parts of water). G128 developer is also used as a replenisher, in which case 3
parts of water are added to 1 part of concentrate.
Fixer
Fixer too is supplied as a concentrated liquid (G328). The same instructions as for pre-
paring developer apply here.
Developing times and bath temperatures
The film is clipped on or slipped into a frame, depending on the type of frame, and hung
in the developer tank. As soon as the film is submerged in the developer, the darkroom
timer is set for the required number of minutes. The optimal developing time is the time
at which the most favourable “contrast to fog ratio” is achieved. Minor deviations from
the correct exposure time may be compensated by adjusting the developing time.
The recommended developing time for Agfa films in G128- manual developer is
5 minutes at 20°C. In the automatic process using G135 developer, the developing time
is 100 seconds at 28°C. Deviating from the recommended developing times and
temperatures will almost always lead to reduced image quality (e.g. increased coarse-
graininess).
Raising the tank temperature will speed up the development process as table 1-10
shows, but the developer will oxidise more rapidly. Should it not be possible to achieve
a bath temperature of 20°C, the following developing times can be used at the
temperatures as indicated in table 1-10. This applies to all D-type films.
The temperature of the developer shall never be less than 10°C, but is preferably
higher than 18°C to obtain optimal image contrast. It is best to always maintain the
same developing conditions, so that the exposure technique can be matched to these
and uniform results obtained.
Film agitation
To prevent air bubbles from forming on the surface of the emulsion (which will cause
spots on the finished radiographs), and to make sure that the developer penetrates all
areas of the emulsion evenly, the films should be kept moving during their first 30
seconds in the developer. After that, it is recommended to move the film from time to
time to prevent film faults such as lines or streaks.
Replenishing
Up to 400 ml of liquid per square meter of film processed may be carried over to the next
tank. When developing frames used it is, therefore, preferable to hold the film
2-3 seconds over the developer tank to drip.
After each square meter of film developed, 600 ml of replenisher must be added to the
bath regardless of the quantity of developer lost from the tank. Up to about 4 litres of
replenisher can be added in this way, for every litre of the original developer in the tank.
The solution must be discarded and replaced with fresh developer when the total
quantity of replenisher added is three times the original total contents, but in any case
after eight weeks, irrespective of the number of X-ray films processed.
Stopbath
Before transferring the developed film to the fixer tank, it is placed in a stopbath
(consisting of 30 ml glacial acetic acid to 1 litre of water) for 30 seconds to prevent the
fixer solution from being neutralized too rapidly by the developer, and stripes or
dichroitic fog from forming on the film.
If a film is not passed through a stopbath, it must be rinsed in running water for a few
minutes immediately after leaving the developer.
Fixing
Fixing renders the image formed during development permanent, by removing unde-
veloped silver halide salts from the emulsion. When the film is taken from the stopbath
it still has a milky appearance; this changes in the fixer and the light areas of the film
become transparent.
As a rule the film is left in the fixer twice as long as it takes to “clear” or become trans-
parent. Fixing time (in a fresh solution approx. 3 minutes) is twice the clearing time
(1.5 min.). As soon as it takes double that time to “clear” a film in G328 fixer solution
at 20°C, it must be replaced.
For every liter of solution in the fixing tank, a square meter of film can be treated.
Films have to be kept moving during the first 30 seconds in the fixing bath.
Final wash
The final wash is intended to remove to remove the residual fixer and the soluble silver
compounds left behind in the emulsion, which if not flushed out, would reduce film
shelf life. Washing should preferably be done with running water, ensuring that all
parts of the film are reached by fresh water. The duration of the final wash depends on
the temperature of the water. See table 2-10. Temperatures over 25°C must be avoided.
Drying in the drying cabinet
When the film is taken out of the water, the water on the film, as a result of its surface
tension, runs together to form droplets of varying size. The film will, therefore, dry une-
venly, causing “drying marks”. For this reason it is advisable to immerse the films in a
solution of 5-10 ml wetting agent to each litre of water. Wetting agent reduces the sur-
face tension of the water so that, after the film has drained, the surface will be evenly
wetted and will dry evenly with no risk of marks. Films should be hung to drain for
about 2 minutes before they are placed in the drying cabinet.
Drying should preferably be done in a drying cabinet, or alternatively in a dry and dust
free room. No drops of water must be allowed to fall on films that are already drying, as
this will cause marks. Wet films should, therefore, always be hung below already
drying films.
Drying time will depend on temperature, air circulation and relative humidity of the air
in the cabinet. Films will dry more quickly when they have first been put into a wetting
agent.
Before a film is taken out of the drying cabinet, it must be checked that the corners and
edges of the film are thoroughly dry. Air temperatures above 40°C should be avoided as
this may cause ugly drying marks. There must be free circulation of air between the
films in a cabinet; if they cannot dry evenly on both sides, they may curl or distort.
Roller dryers
Industrial dryers can be used to dry films quickly and uniformly after washing.
This mechanised drying process only takes minutes. Dryers and chemicals should
preferably be matched. There are compact roller dryers on the market which are
capable of developing approx. 15 cm of film per minute and take up far less space than
a drying cabinet.
Use of the characteristic (density) curve with an exposure chart