A standard for each color processing chemical should be established. What
the standard should be depends on many factors: the particular laboratory,
the type of work, the type of processes, etc. Due to many variables that
may be beyond your control, the established standard must have upper and
lower control limits to allow a minimal amount of deviations and still
produce an acceptable product.
Some of these variables are: a change in
agitation from one person to another, not following the manufacturer's
recommendations when mixing, the age of the chemicals, the use or misuse of
replenishment, or even the rate. Any of these items can cause problems in
the color process.
Specific gravity, pH, and sensitometric analysis are
used to analyze the color processing solutions to assure the highest quality
in the chemicals, therefore assuring a high quality end product.
a. Specific Gravity Analysis. Specific gravity is a check to determine
if proper amounts of chemicals and water are present in a solution.
Specific gravity may be defined as the following: the mass of a volume of a
substance compared to an equal volume of pure distilled water.
(1) How specific gravity analysis works. As chemicals or water are
added to or subtracted from a chemical solution, the specific gravity of the
solution will change.
When chemical solutions are mixed and the specific
gravity is determined, it should be the same as the specific gravity of any
previously mixed solution.
(a) If the measurement registers higher than the previous reading
it would indicate that more than the formula amount of the chemical
ingredients have been added to the solution, a foreign ingredient has been
added, or the solution has not been diluted adequately.
(b) A specific gravity reading that is lower than the previous
readings would indicate that an ingredient had been left out of the solution
or too much water had been added.
(2) Setting a standard. To certify a chemical solution, first set a
To set a standard, take specific gravity readings each time a
developer or any chemical solution is mixed.
After several readings have
been taken, determine the average reading. This average can then be used as
(a) Establish upper and lower control limits.
represent the amount of deviation from the standard that a solution may be
and still obtain an acceptable product.