Chemical Analysis
line until it intersects the bold line labeled .9 (0.90
gamma). From this point, drop straight down to the
time of development line and read 7.5. It takes 7 1/2
minutes of developing time at the recommended
Much of the chemical analysis performed is
accomplished by using common sense. Practices,
such as cleanliness, accuracy, and proper preparation
of solutions, should be observed at all times.
Contamination can ruin a developer which, in turn,
could ruin your images. Things, such as dirt and dust,
in the solution can cause artifacts on the film.
Before equipment is used for mixing and
measuring chemicals, you should clean it thoroughly.
Use a good-quality medium-strength detergent to wash
glassware and other vessels. Be sure that all washed
items are rinsed well with clean tap water. Keep the
entire area clean to prevent contamination and ensure
Some of the more common chemical analysis
methods you will use are as follows:
Determining pH
Measuring specific gravity
The equipment and methods used presently for
mixing photographic solutions are the result of
changes that have taken place over many years.
These improvements are made to keep pace with
improved sensitized materials, processing equipment,
and environmental regulations.
Substandard solutions make it impossible to
operate a processing system within controlled limits.
The preparation and use of photographic solutions
must be a systematic procedure based on accurate
measurement and standardized methods. High-quality
standards can be achieved only when the conditions of
exposure, chemistry, and processing are all within
operating tolerances. Then results are predictable.
In certain critical processing areas, chemical
analysis is used to check solutions before and during
use. This helps us to keep chemicals up to standard.
Analysis of the components of processing solutions is
often used as a basis for discarding solutions or
adjusting their composition for future use. These
procedures are used to determine proper replenishment
rates to promote the efficient use of chemicals.
Quality assurance procedures are implemented, so
solutions are mixed, used, and discarded properly.
Sensitometric testing
Although there are several reasons for certifying
photographic solutions, the principal objective is to get
desirable, predictable, and consistent results.
Control of a photographic process requires that the
chemical activity of the solutions be maintained.
Chemical analysis procedures used to indicate
chemical activity are valuable only when the samples
analyzed are representative of the processing solutions.
The analysis of a sample taken improperly may do
more harm than good in controlling the process.
Processing solutions may be clouded or contain
floating particles, dispersed oil droplets, or a
precipitate. Even a clear solution may have different
concentration levels in various parts of a processing
tank; for instance, the chemical composition at the
point where the film enters may not be the same as in
other parts of the tank. To compensate for this, you
must use a prescribed procedure, so all the samples
are taken from the same location, such as from a point
near the tank overflow. These samples should be
representative of the solution at an established

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