Chapter 12
Darkroom
Procedures
Darkroom Procedures
 To
repeat what was previously said
about the composition of x-ray film, it
has a base of cellulose acetate covered
on both sides with a sensitive emulsion
of silver halides (silver bromide,
chloride & iodide).
 Today plastic polyester is used.
Darkroom Procedures
 When
this emulsion is exposed to
radiation or light (from screens or other
sources) an unexplainable change takes
place that cannot be seen.
 The change is produced in the physical
& chemical structure of the emulsion.
Darkroom Procedures
The change produced on the emulsion
depends upon the amount of x-ray & light
reaching it.
 Since the body part being radiographed
absorbs some of the radiation being directed
at it, we can see that the amount reaching
the screens & the film depends upon the
intervening tissue.

Darkroom Procedures
For example, bone absorbs more x-ray & fewer
rays get through to the film/crystals.
 Therefore, fewer crystals are activated.
 The areas outside the parts receive the total
amount of radiation & in this area structural
change is complete.
 The portion of the film under the lead marker
(and any other structure that absorbs all the
radiation) receives none & there is no structural
change to the silver halide crystals.

Darkroom Procedures
The other tissue areas absorb the x-rays in
varying degrees depending upon the
thickness & density of the parts & thus the
film & screens under these parts receive
varying degrees of x-ray & the screens glow
in varying degrees & thus the change in the
emulsion varies from place to place.
 A Latent image is formed in this way.

Darkroom Procedures
 We
can therefore see that the latent
image must be a complete one.
 The purpose of dark room
procedures is to change the latent
image to a photographic one.
Film Processing Chemicals
 Various
chemicals are used in the
processing of the radiographic film.
 Of the ones discussed here, the
developer & the fixer must be used; the
developer replenisher, the fixer
replenisher & the acid stop-bath may
or may not be used.
Film Processing Chemicals
 There
are other chemicals used for
special purposes (intensification of
under-developed film, reduction of
over-developed film), but they will not
be discussed.
 Directions for their use will be found
on the package.
The Developer
 Developing
is actually the reduction of
the exposed silver halides to metallic
or elemental silver (the converting of
the latent image to a visible image).
 The developer causes a reaction of the
silver halide crystals & thus makes
them visible.
The Developer
 This
is done through a pair of
redox reactions where an electron
is made available to unite with a
silver ion that has a single (+)
charge (from light hitting the film),
thus reducing the silver ion to
metallic/elemental silver.
The Developer

Reducing Agents
– change the exposed silver halides to black metallic
silver; elon (for detail) is balanced with
hydroquinone (for contrast).

Accelerator/Activating
– maintains the proper alkalinity for the developer to
work & also swells the gelatin. Accelerating agents
include sodium carbonate or sodium hydroxide.

Prolonged exposure to these may result in
dermatitis due to its alkalinity
The Developer

Preservative
– prevents oxidation of the developing agents by
having a greater affinity for O2 than the
developing agents themselves. The preservative
used is sodium sulfite.

Restrainer
– slows down the development rate in order to
prevent fogging. Potassium bromide &
potassium iodine are the agents used.
The Developer
 Dissolving
Agent
– used is water.
 Hardening
Agents
– used in automatic processors &
functions to prevent excessive
emulsion swelling. These agents
include gluteraldahyde.
The Developer Replenisher
 In
using the developer the bromide
removed from the film builds up & acts as
a restrainer for prolonged developing
time. Developer replenisher, which is a
supercharged developer with no
restrainer, can be added to the developer
tank to bring the solution up to a proper
level while also bringing it back to its
proper strength.
The Acid Stop-Bath
 This
is absent in all automatic
processors as the rollers within the
processor function to squeeze off the
developer.
 In manual developing, the acid stop-bath
can be used after the film leaves the
developer to stop the development
immediately.
The Acid Stop-Bath
 It
is a weak acetic acid solution that
neutralizes the alkaline developer.
 Acid stop-bath is not usually used
because it necessitates having an extra
tank. The film is usually rinsed in the
water tank to remove most of the
developer before putting it into the fixer.
The Fixer
 Fixation
involves two separate processes:
The “clearing” of the film of unexposed
silver halide salts which are not affected by
the developer &which would turn black if
exposed to light (these have not been reduced
by the developer).
The “hardening” of the emulsion.
The Fixer
 The
darkroom lights may be turned on as
soon as the film has cleared since there are
than no light sensitive elements in the
emulsion.
 Clearing Agent
– removes the unexposed silver halide salts from
the film (sodium thiosulfate, a.k.a. hypo).
Most modern fixers use ammonium
thiosulfate.
The Fixer
 Hardener
– reduces the swelling & softening of the
emulsion produced by the alkaline
developer & hardens it (potassium alum).
 Preservative
– maintains proper acidity of the solution &
prevents early breakdown of the clearing
agent (sodium sulfite).
The Fixer
 Acidifier
– neutralizes the alkaline developer
carried over & keeps the medium
acid for the hardener to do a full job
(acetic or sulfuric acid).
 Dissolving
Agent
– used is water.
The Fixer
 In
manual developing chrome alum
may be used as a hardener instead of
potassium alum.
 This makes the fixer opaque to light.
 Therefore, the lights may be turned on
as soon as the film is put into the fixer
with out harm.
The Fixer Replenisher
 Replenisher
for the fixer is
available but care must be taken to
remove enough of the old solution
before adding the replenisher for
solution carried out must be
balanced by solutions carried in.
Steps in Film Processing
Before beginning to process film the
developer & fixer should be stirred with
separate paddles.
 The temperature should be as close to 680 as
possible.
 Developing times & temperatures may vary.
 As a rule with increased temperature you
decrease the developing time & vice versa.

Steps in Film Processing
 The
film is removed from the
cassette & clipped into a film
hanger.
 The cassette should be closed to
avoid staining of the screens with
solutions during processing.
Steps in Film Processing
 The
film is than passes through the
following five steps (four with
automatic processing):
Developing
Rinsing
Fixing
Washing
Drying
Steps in Film Processing
 Developing
– developing of the film may be done by:
1) sight (under a safelight of course)
2) by time & temperature charts which
are available.
– The average time developing temp/time
is 680 for 5 minutes.
Steps in Film Processing
Time & temperature is recommended because
the opacity of the uncleared film & the length
of time for the eye to accommodate to the
darkness makes inspection of the film difficult
& prolonged exposure to the safelight can fog
the film.
 In either case the film should be agitated for
the first few seconds in the developer to
remove any air bubbles on the film surface that
would restrict development in that area.

Steps in Film Processing

Rinsing
– After development the film should be rinsed in clear
water (running) for 30 to 45 seconds to remove as much
of the developing chemicals as possible to stop
development & prevent contamination of the fixer with
alkaline developer.
– An acid stop-bath may be used in place of the rinse, but
in using either the film should be drained before putting
it into the fixer.

In automatic processing the rinsing stage is
removed
Steps in Film Processing

Fixing
– We have previously described the actions of the
fixer as “clearing” & “hardening” of the
emulsion. These two processes occur
simultaneously but the latter takes
approximately twice as long.
– The clearing time is usually 3-4 minutes but the
film is left in the fixer for 10 minutes for
hardening.
Steps in Film Processing

Washing
– The finished film should be composed of
metallic silver embedded in gelatin & nothing
else. The film must be thoroughly washed to
remove all chemicals to prevent discoloration &
fading of the image.
– Films should be washed 15 minutes in clear
running water, depending upon the rate of flow,
temp., type of film used & the type of fixer
used.
Steps in Film Processing
 The
longer the film spends in the
fixer, the longer the wash time
needed.
This
is a 1:2:3 ratio of
developer to fixer to wash.
Steps in Film Processing
Drying
 The ideal situation for drying of x-ray film
is a film drying box that combines a heating
element with a circulating fan. It can dry in
15 minutes.
 Film will dry properly if hung in air for a
longer period (1+ hours).
 A fan aimed at the edge of the film will
speed up the process.

Replenisher Method & Exhaustion Method
 Both
the developer & the fixer may be
either replenished to maintain the
timing or used until exhausted by
increasing the time element.
 Both methods are satisfactory but the
replenisher method saves time, does
not involve record keeping & is less
expensive.