Operating Manual

The unexposed area on the PMC-strip shown in figure 2-10, apart from providing a
reference for fog and base density, also allows for the Thio-Test to be carried out.
The components used for this test are:
1 The Thio-Test colour step-wedge
2 A dropper-bottle of Thio-Test reagent
The reagent consists of a 1 % silver nitrate solution in demineralised water
The working method, which only takes a few minutes, is as follows:
1 apply the test liquid (reagent) to an unexposed part of undeveloped, dry film
2 allow to soak for 2 minutes,
 15 seconds
3 remove excess liquid with absorbent paper
4 leave to dry for 1 minute before treating the reverse side
5 repeat the above procedure on the other side of the film, in exactly the same spot.
Evaluate as follows, within 30 minutes:
6 the test zone of the film is put against a white background
7 the Thio-Test colour strip is put on the film, as close to the spot as possible
8 the colour step of the wedge that resembles the colour of the test zone closest,
is regarded definitive for life expectancy.
A regular Thio-Test provides early detection of deficiencies in the development process,
for example exhausted fixer solutions, irregular water supply or insufficient rinsing, and
so prevents poorly processed films being archived.
10.7 Storage of exposed films
The way in which radiographs are handled and stored plays a very important role in their
keeping properties. Films that must be kept for longer periods of time require the same
ambient conditions as new unexposed films, i.e.:
• ambient temperatures below 24°C
• relative humidity of less than 60 %
• preferably stacked on edge
9594
A PMC-strip as shown in figure 2-10 has to be used whenever the chemicals in an auto-
matic or manual processing system are replenished or changed. It is also advisable to use
a PMC-strip regularly, but at least once a month, for a routine check of the development
system.
A calibrated densitometer measures the following steps:
D
0
: fog and base density (  0.3)
D
3
: density of step 3
D
7
: density of step 7
The reference values according to the corresponding certificate are S
r
and C
r
.
The following calculations are then made:
• Sensitivity index S
x
= D
3
– D
0
• Contrast index C
x
= (D
7
– D
3
)
.
S
r
/S
x
The system is acceptable if the following criteria are met:
a. D
0
=  0.3
b. S
x
has a value  10 % of S
r
c. C
x
has a value between C
r
+15 % and C
r
–10 %
If one or more of these criteria are not met, the development process must be adjusted.
Thiosulphate-test to check film archiving properties
The archival properties of a radiographic image must also be determined in accordance
with the standards ISO and EN by analysing the quantity of residual thiosulphate in the
film’s emulsion layers. This quantity depends on the thoroughness with which the fixing
and rinsing processes have been carried out.
For storage over a period of 100 years, 100 g/m
2
is allowed; for a period of 10 years dou-
ble this figure is allowed, see table 3-10. These values are difficult to measure however.
The so-called Thio-Test, developed by Agfa, is a very useful and quick method to quantify
film-keeping properties in practice.
Unexposed area for the Thio-Test
fog + base density
Fig. 2-10. PMC-strip with an unexposed area
for the Thio-Test
Reference step
for film sensitivity
Table 3-10. Colour steps for the Thio-Test . (*)These values apply to films with double-sided emulsion layers.
Reference step
for film contrast
Colour wedge Thiosulphate Archival quality
(from dark to light) (*)g/m
2
L.E. (Life expectancy)
Darkest Min. 0.35 Film needs
repeat treatment
Dark Max. 0.20 L.E. 10 years
Light Max. 0.10 L.E. 100 years
Lightest max. 0.04 L.E. 500 years