You should consult the film data sheets or the
Photo-Lab-Index for the recommended developers for
each particular type of film to be processed.
CHANGES IN DEVELOPER WITH USE
The function of a developer is to change chemically
the sensitized material treated in it. It stands to reason
then that a chemical change also takes place to the
developer itself. Most developers are used more than
once. Therefore, you must know what changes to the
developer can be expected and what can be done to
prevent them or at least compensate for them. The
primary changes that occur to a developer as it is used
are as follows:
Some developer is removed or carried out with
the film and on the film hangers or reels.
The developing agents are used up by reduction
of silver halides to black metallic silver and by aerial
oxidation. When the developing agents are used up by
the reduction of silver halides, the by-products of the
reaction cause the pH of the solution to drop, thus
becoming more acid. When the developer agents are
used up by oxidation, the pH tends to rise.
The preservative is used up, thus the developing
agents oxidize faster.
The bromide within the solution is increased
because the bromide is released from the film emulsion
itself.
The effects of these changes to a developer are as
follows:
The development time required to reach a given
contrast index or gamma is increased. Therefore, when
a developer is used over and over, development time
must be increased as more film is developed.
The effective film speed produced by the
developer decreases because of the increased bromide
(a restrainer) in solution. However, this speed loss may
be partially offset by increasing development time to
maintain image contrast.
Complete exhaustion of a developer occurs when
the developing agents are all used up. The approach of
exhaustion is characterized by a brown color of the
solution. Since a developer in this state can stain
sensitized materials, it should not be used.
In most Navy imaging facilities, it is not economical
to use a developer to the practical exhaustion point and
then discard it. The quality of the image usually suffers
long before the exhaustion point of the developer is
reached. Replenishers are usually used to prevent this
from happening.
Replenishment of a developer involves replacing
those chemicals in the used developer that are exhausted
by a replenisher so that the developer remains
consistent. The aim of replenishment is not to keep the
composition of the developer constant but to keep its
activity constant.
There are two commonly used methods of
replenishment. The first or “topping off” method is used
extensively in tank processing. When topping off is
used, the developer solution is maintained at a constant
level in the tank by adding replenisher, so the volume
added is equal to the amount of developer carried out.
When you are replenishing by this method, it is possible
to maintain consistency in development for only a
certain period of time. After a given volume of
replenisher has been added to the developer, the
developer must be discarded. This procedure is then
repeated with new developer.
The second replenishment method is called the
"bleed" method. The bleed method is used primarily
with machine processing where a circulating developer
system is used. In the bleed method, used developer is
drained off and replenisher (in proportion to the amount
of film processed) is fed in, so the characteristics and
the level of the developer in the machine remain
constant.
FIXING, WASHING, AND DRYING
As soon as a light-sensitive material is developed,
it contains a visible silver image, but the image is not
ready to be exposed to light. Only a portion of the silver
halides in the emulsion were reduced to black metallic
silver by the developer. The silver halides that were not
reduced restrict both the immediate usefulness and the
permanence of the image. These undeveloped silver
halides must be removed. This is the purpose of the
fixing bath. Before treating the sensitized material in the
fixer (as it is called), you must stop or at least slow down
the action of the developer. When the light-sensitive
material is removed from the developer solution, there
is a small amount of developer both in the emulsion and
on the surface that must be removed or neutralized. For
this, you use either a water rinse bath or an acid stop
bath.
10-4
