b. Clearing Agent. The clearing agent (sodium thiosulfate or ammonium
thiosulfate) dissolves the residual unexposed silver bromide crystals in the emulsion
without damage to the silver image. The unexposed crystals have of course, been
unchanged by the developer. If the film is not properly cleared, the remaining
unexposed silver bromide crystals will darken on exposure to light and obscure the
radiographic image. These chemicals are commonly known as "hypo." The clearing
action of hypo involves a chemical reaction between the sodium or ammonium
thiosulfate and the silver bromide in the emulsion, wherein silver thiosulfate is formed
and remains in solution.
c. Hardener. The hardening agent (platinum alum, chrome alum, or aluminum
chloride) decreases the possibility of physical injury to the gelatin emulsion. A swollen
emulsion is easily scratched or distorted during the washing and drying process. The
hardener restrains swelling of the gelatin and hardens it so that it can withstand the
normal effects of processing.
d. Preservative. The preservative (sodium sulfite) prevents decomposition of
the clearing agent by the acid with a resultant precipitation of sulfur, as long as normal
developing temperatures are maintained. It assists in clearing the film and prevents the
residual developer carried over in the film from oxidizing and discoloring the fixing bath.
Section IV. HANDLING AND STORAGE
X-ray film is packaged in hermetically sealed foil and paper wrappings to protect
it from light and moisture in quantities of 25 and 75 sheets. Each film is in a folder of
chemically pure interleaving paper. (Some manufacturers omit the interleaving paper.)
Each quantity of either 25 or 75 sheets is placed between cardboard, wrapped in
protective paper, and placed in a metal foil bag sealed to ensure approximately 50
percent relative humidity inside the package. The package is then wrapped in paper
and placed in a metal foil bag sealed to ensure approximately 50 percent relative
humidity inside the package. The package is then wrapped in paper and placed in a
cardboard carton. Packed in this manner, x-ray film will be free from any defects due to
excessive humidity as long as it remains in the unopened foil wrapping. For overseas
shipments, each carton is sealed in heavy waterproof paper for additional protection.
X-ray film is delicate and should not be handled carelessly or roughly. Avoid
touching its surfaces, holding it as near the edges as possible with clean, dry hands. It
is sensitive to maltreatment of any kind; heat and light adversely affect the emulsion. It
can be handled safely and rapidly for all radiographic purposes as long as the x-ray
specialist uses precaution to avoid the production of foreign marks (artifacts) on the film.