rapidly enough to cause boiling or a splashing explosion
that may splash the solution on someone nearby. Acids
should always be poured slowly into a solution (near the
edge of the container) while rapidly but carefully stirring
the liquid.
Mixing tanks, storage tanks, and machine tanks for
developer, stop bath, fixer, and other solutions must be
labeled clearly with waterproof tape or nameplates to
reduce the chance of putting a solution into the wrong
tank. The label should contain the name of the solution,
the date it was mixed, and the name of the person that
mixed it. It is also mandatory that hazardous chemical
labels be attached to all chemical containers.
All of the mixing equipment and the mixing area
must be cleaned immediately after use to prevent
solution contamination. The mixing tools and tanks
must be thoroughly cleaned right after use to prevent
dried solutions from forming encrustations that could
dissolve when a new solution is mixed. Mixing tools that
have not been used in some time should be washed
before use to remove any dust or dirt that may have
When mixing photo chemicals, you should always
start with clean tools and a clean tank with the right
amount of water-usually about one half to three fourths
of the final volume. The temperature of the water must
be as specified in the instructions. Developers are
generally mixed at or about 90F to 125F, while fixers
are mixed in water that should not be much above 80F.
Always dissolve or dilute ingredients in the order
called for by the instructions. Dry ingredients must be
completely dissolved before the next ingredient is
added. All liquids must be completely diluted, while
stirring, before the next ingredient is added.
After a liquid is added to a solution, rinse the bottle
and add the rinse water to the solution, so all the
concentrated liquid is used.
After all ingredients have been combined and
thoroughly dissolved, diluted, and mixed, water should
be added to bring the solution up to the correct volume.
Do not forget to mix this water thoroughly into the
Before mixing photographic chemicals, you should
read the manufacturer's directions carefully. Much
research goes into the production of chemical products;
however, it is only effective when the chemical is mixed
and used properly. The directions for even the most
familiar product should be reviewed, because there are
continual attempts to improve photographic materials;
for example, new film or developer combinations may
call for changes in dilution, processing time, or
temperature to get the required results. Learn to follow
directions. This is very important in the preparation of
chemicals for both quality and safety reasons.
Remember to follow the proper procedures for
chemical safety. You should prepare the chemicals in a
well-lighted and well-ventilated room. Do not taste or
inhale any chemical. You are required to wear rubber
gloves, a rubber apron, eye protection, a long sleeve
shirt, and a respirator for your personal protection.
Remember, for safe mixing and quality results,
In most imaging facilities, it is common
practice to connect a hose to the water spigot to
aid in filling a chemical mixing tank and to
prevent splashing in the sink. Aboard ship,
hoses attached to potable water spigots can back
siphon chemicals from the tank or sink into the
drinking water supply. Such hoses should either
be removed after each use or have a backflow
preventor installed in the plumbing system.
You must know how to prepare percentage solutions
from liquid chemicals. When the chemical on hand is in
liquid form and of known strength, a percentage solution
can easily be prepared by the following method:
Amount Wanted x Strength Desired
Strength on Hand
Multiply the amount wanted by the strength desired
and divide the product by the strength of the chemical
on hand; for example, you need 11 ounces of 28 percent
acetic acid. The chemical on hand is glacial acetic acid,
99.5 percent. Thus,
11 x 28
= 99.5 = 3.09 = 3 ounces

Basic Photography Course

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