dust or fumes can ruin these materials. There should be
adequate ventilation, a complete air change every 3
minutes, and an exhaust fan to the outside atmosphere
in the area where chemicals are mixed.
Containers for photographic solutions should be
made of a material that does not affect or is not affected
by chemicals. Glass is the best material. Stainless steel
is a highly suitable material, provided it is of the proper
composition. Hard rubber and glazed earthenware may
also be used satisfactorily. Acid and alkali-resistant
plastic containers are acceptable.
Containers, graduates, sinks, and every utensil used
in the photographic lab should always be clean. As soon
as work is finished with an item of equipment, it should
be cleaned and returned to its proper place. When
chemicals are spilled, clean them up as soon as possible.
Chemical solutions and chemical dust corrode and
cause pitting of most materials, including stainless steel,
when allowed to remain for any length of time.
Photographic quality suffers when the chemicals are
improperly mixed. You must be certain that the amount
of chemical you put into a solution is the amount
The mixing of processing solutions has been greatly
simplified over the years by the introduction of
packaged photo-processing chemicals. Packaged
chemicals come in convenient sizes for most needs.
They offer standardized quality, economy, and
Packaged chemicals include film and paper
developers and fixing solutions of various types that are
manufactured under tightly controlled conditions. These
packaged chemicals are available in either liquid or
powder form. Processing solutions can be mixed easier,
faster, and more accurately with packaged chemicals
than with bulk chemicals.
When mixing packaged chemicals, you should
always mix the entire package. Packaged chemicals
usually contain more than one ingredient. During
shipping and handling, these ingredients may separate
with the heavier elements settling to the bottom of the
package. When only part of the package is mixed, some
of the ingredients that have separated or settled may not
be put into the solution and the result of the process is
not predictable.
Always add chemicals to the water or solution Dry
chemicals should be poured slowly into the water while
it is being stirred. When preparing a developer, be
careful while you are stirring so air is not beaten into the
solution. When water is poured on dry chemicals, they
will cake and form hard lumps that are difficult to
Lumps or hard particles should be ground up, or
crushed, with the stirring rod or with a pestle. Never add
another chemical to a solution before the previous part
has been completely dissolved Sometimes there is a
residue that will not dissolve. The residue may be sand
in the water supply, impurities in the chemicals, or other
matter that found its way into the water; however, when
the solution is allowed to stand for awhile, these
particles usually settle and the clear liquid can be poured
off. To remove sludge or dust particles that may not
settle, pour the solution through a funnel containing
three or four layers of cheesecloth or absorbent cotton.
Many chemicals are very sensitive to heat, and even
moderate temperatures seriously affect their chemical
properties. However, the rate of chemical reaction
increases with an increase in temperature, and all
chemicals dissolve more readily in warm water than in
cool water; consequently, many formulas and
instructions recommend that water as hot as 125F be
used to prepare the solution that must then be cooled to
the correct processing temperature. You should always
try to mix solutions at the minimum temperature
recommended by the manufacturer. Solutions oxidize
faster at higher temperatures because of increased
chemical activity at these temperatures.
When all crystals are dissolved, the solution should
be practically colorless. Sometimes a solution appears
cloudy or milky for a short time after it is mixed. This
appearance may be caused by air taken into the solution
by the dry chemicals. Air taken into a solution is
distributed through the solution as tiny bubbles that
cannot escape while the solution is being stirred. When
the presence of bubbles has caused the discoloration, the
solution will clear up when it is allowed to stand for a
while. The bubbles rise to the surface of the solution and
escape into the air.
Always add acid to the water. This is as easy to
remember as AAA (Always Add Acid). It is dangerous
to pour water into an acid. Some acids generate heat

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