complete washing of the material and to control or
eliminate waste.
If the wash-water temperature is allowed to drop to
65F (18C) or below, emulsion staining may result. As
the temperature decreases, less emulsion swelling
occurs, reducing the effective penetration of fresh water
supplied to the emulsion. When the emulsion does not
swell, the chemical-laden water does not get out through
the emulsion surface. These retained chemicals can
cause stains.
The wash water flow rate is another important factor
to consider. This rate must be high enough to wash the
material, but no more. When insufficient water flow is
supplied to the machine, crystallized chemicals may be
seen on the material, and additional staining can result.
You must not adjust the water flow rate higher than is
needed. A few extra gallons-per-minute flow rate may
not seem important; however, over time this effect can
be extremely costly, particularly aboard ship.
In machine processing, the temperature may vary,
depending on the machine and the kind of processing
being performed. High-speed processing machines
operate at higher solution temperatures. Temperature
control is critical and must be maintained to produce
correct results. Although this may be considered a
variable factor, the temperature is controlled
automatically by processing machines. In some
machines, the solution tanks are immersed in a
temperature-controlled water jacket. By controlling the
water temperature within the water jacket, you can
control the temperature of the solutions inside the tanks.
In other machines, the solution temperature is directly
controlled by separate heaters or heat exchange control
units in the recirculation system. A temperature probe in
the solution tank monitors and controls the temperature
control unit.
The solution levels of a processor must be checked
before processing material. If the solution level is too
low, stains, improper tracking, and roller marks may
affect the film or paper. When the machines are shut
down for a period of time, some evaporation occurs.
Since only the water from the solution evaporates, you
must top off the solution tanks with water before
processing material. There is a certain amount of
carry-over of solution from one tank to another within
the machine. Usually, chemical carry-over is minimized
with roller squeegees. When the replenishment rate of
the processor is set properly, this carry-over is
compensated by supplying fresh chemistry to the
solution tanks.
Most processing machines use relatively large
quantities of solutions to carry out the process properly.
However, even considering the large quantities
involved, certain chemical components within a given
solution are used up at varying rates. In addition, there
are certain reactions that form by-products that build up
in the tank of the processor; for example, bromide (a
restrainer) gradually builds up in the developing
solution. Also, there is a certain amount of carry-over of
solutions from one tank to another. This causes a
continuous change in solution strength and solution
purity. The replenisher solution replaces the used
chemicals, dilutes the excess chemicals or by-products
that have built up, and replaces the solution lost by
carry-over and evaporation.
The replenishment system used in machine
processing is called the bleed method. When the bleed
system is used, a calculated amount of replenisher
solution is added and forces some of the used solution
out through an overflow drain in the solution tank. You
must check the established replenishment rates as well
as the replenisher holding tanks before and during
processing. Inconsistent results occur when the process
is not replenished correctly.
After the material is processed and washed, it
continues through the machine into the drying cabinet
where moisture is removed. The drying cabinet is more
than a heated compartment for the processed material.
In a majority of machines, both the temperature and the
humidity of the cabinet are carefully controlled. Too
little drying causes the emulsion to be tacky, whereas
too much drying may produce excessive curl and
brittleness. Brittleness, once it occurs, cannot be
eliminated; so it must be prevented. Both the
temperature and the relative humidity must be adjusted
for the speed of the machine and the type of material
being dried.
Under ideal conditions, the drying cycle should
yield a stable 50 percent relative air humidity. To lower
the relative humidity of air, you must heat the air; this
accelerates the evaporation of moisture. The rate of
evaporation and the relative humidity are directly

Basic Photography Course

Privacy Policy