Film processing
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1
Objectives
• Explain the process of film development
• Describe synergistic properties of automatic
processor reducing agents
• Identify primary chemical and its function
for each developer and fixer agents
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Objectives
• Explain process of film fixation
• Explain the washing and drying processes
of film archiving
• Describe the functions of the subsystems of
an automatic processor
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Objectives
• Discuss radiographic darkroom design
– Entrances
– Pass boxes
– Centralized and decentralized plans and
ventilation
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Objectives
• Explain rationale for use of silver recovery
systems
• Compare advantages and disadvantages of
metallic replacement, electrolytic, chemical
precipitation, and resin silver recovery units
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Purpose of Film Processing
• To accumulate enough black metallic silver
at sensitivity specks to yield a visible image
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Purpose of Film Processing
•
Film processing involves four steps:
1.
2.
3.
4.
Developing
Fixing
Washing
Drying
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Developing
• Visibility of silver at latent image sites
• Consists of:
– Reducing agents (primary agent)
– Activator
– Restrainer
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Developing
• Visibility of silver at latent image sites
• Consists of:
– Preservative
– Hardener
– Solvent
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Reducing Agents
• Provide free electrons to silver ions
– Through “gates” of exposed sensitivity specks
• Reduction/oxidation
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Reducing Agents
• Two reducing agents
work synergistically
– Phenidone (P
developer)
• Works quickly to
produce shades of
gray
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Reducing Agents
– Hydroquinone (Q developer)
• Works slowly to produce black areas
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Reducing Agents
• Used developer becomes oxidized
• If not properly replenished it changes color:
– First, deep amber
– Next, brown
– Finally, rust red
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Activator
• Typically sodium carbonate
– Added to developer to maintain an alkaline pH
• Helps reducing agents get to silver halides
– Swells gelatin making it easier to penetrate
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Activator
• Makes developer solution caustic
– Rubber gloves and apron should be worn
– Neutralize spills with fixer or dilute with water
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Restrainer
• Typically potassium bromide
– Provides a “distraction” to overactive reducers
– Prevents developer from acting on unexposed
silver halide crystals
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Preservative
• Developer is easily oxidized by air
• Sodium sulfite decreases this oxidation
process
• Additionally, careful tank design can reduce
the developer’s exposure to air
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Hardener
• Glutaraldehyde
– Controls swelling of gelatin
– Prevents abrasions during processing
– Maintains uniform film thickness
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Hardener
• Low levels of hardener allow gelatin to
stick to rollers
– Can cause processor jams and/or artifacts on
films
– May present as moist, sticky films even after
being dried
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Hardener
• Too much hardener will harden emulsion
too soon
– Prevents chemical interactions from happening
– Traps moisture in gelatin
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Solvent
• Water
– Should be filtered
• 5-10 micrometer filter
– In tropical areas
• Should be treated for bacteria and fungi
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Contamination
• Developer is impacted by contamination
– 0.1% of fixer present in developer will stop
action of reducers
– Results in gray, low contrast films
• Developer is carried into fixer tank
routinely
– Thus, developer does not contaminate fixer
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Contamination
• Can be avoided by using splash guards
• When cleaning processor
– First, fixer tank should be filled
– Second, developer tank should be cleaned
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Contamination
• When shutting down processor
– Lid should be opened
– Prevents fixer condensation from dripping into
developer tank
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Fixing
• Undeveloped silver halides must be
removed from film
• Consists of:
– Clearing agent (primary agent)
– Activator
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Fixing
• Consists of:
– Preservative
– Hardener
– Solvent
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Clearing Agent
• Usually ammonium thiosulfate
• Bonds with unexposed silver halides
– Becomes ammonium thiosilversulfate
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Clearing Agent
• Films will appear milky if not properly
cleared
• Typical clearing time is 15-20 seconds
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Activator
• Acetic acid maintains an acidic pH
• Enhances function of clearing agents
• Neutralizes developer solution
– Stops action of reducers
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Preservative
• Sodium sulfite
– Removes silver from ammonium
thiosilversulfate
– Allows the ammonium thiosulfate to continue
to remove silver halides
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Hardener
• Glutaraldehyde only works in alkaline
• Fixer hardener is aluminum chloride,
chromium alum, or potassium alum
• Serves same purpose of developer hardener
– Maintains film thickness
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Solvent
• Filtered and treated water
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Depletion
•
•
•
•
Fixer eventually becomes silver saturated
Clearing time gets longer
Replenishment prevents depletion
Silver recovery removes silver from used
fixer solution
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Washing
• Water removes as much chemistry as
possible
• Temperature should be 5oF (3oC) lower than
the other solutions
– If too cool, emulsion will reticulate
• Film will have a crackled appearance
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Washing
• If fixer is not washed from film
– Film will become yellow, then brown with age
• Proper washing
– Requires agitation and enough time
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Washing
• Wash tanks are prone to algae and bacteria
growth
– Tank should be drained when processor is shut
down
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Drying
• Accomplished by forcing hot air over both
sides of the film
– 120-150oF (43-65oC)
• Hardens the emulsion and seals supercoat
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Storage
• 70oF (23oC) and 60% humidity
• Length of storage dependent on state law
and institution
– Usually 5-7 years
– Minor and legal cases indefinite
– Mammograms
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Transport System
• Transport racks
• Crossover networks
• Drive system
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Transport Racks
• Three series of rollers
– Provide constant tension to move film through
each tank
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Transport Racks
• Turnaround equipment at bottom of each
tank
– Master roller
– Planetary rollers
– Guide shoes
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Crossover Networks
• Similar to turnaround equipment in
transport racks
• Misaligned guide shoes can scratch films
• Entrance rollers
• Film feeding
– Always straight along the short axis
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Drive System
• Series of gears and mechanical devices turn
rollers
• Driven by single motor
• Speed of motor determines length of time
for processing
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Dryer System
• Squeegee crossover rollers
– Remove excess water
• Hot air blown through slotted tubes
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Replenishment System
• Replaces chemicals as they are depleted
• Two types of replenishment
– Volume replenishment
– Flood replenishment
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Developer Starting and Seasoning
• Starter solution
– Acetic acid and potassium bromide
• Must be added to fresh developer chemistry
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Developer Starting and Seasoning
• Seasoning
– Adequate mixing of developer chemistry
necessary
– Requires running processor for 15-20 minutes
prior to processing films
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Replenishment Rates
• 4-5 ml of developer/inch of film
• 6-8 ml of fixer/inch of film
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Processor Solution Safety
•
•
•
•
•
•
Hazardous materials
OSHA
EPA
MSDS
Protective eyewear/eyewash
Rubber gloves and apron
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Circulation System
• Stabilizes temperature
• Agitates and mixes chemistry
• Filters solutions
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Temperature Control System
• Maintains all three solutions at compatible
temperatures
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Darkroom
•
•
•
•
Safelights
Entrance
Pass box
Plan
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Safelights
• Kodak GBX filter
–
–
–
–
Dark red
Low intensity (7 – 15 watts)
4 feet from work area
Direct illumination possible with most films
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Safelights
• Kodak Wratten Series 6B
– Orange-brown (amber filter)
– Safe for films sensitive to blue/violet light
55
Safelights
• LED
– Light emitting diode
– High initial cost
– Long lasting
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Safelights
• Too many can result in too much light
intensity
• Benches and flooring
– Light coloring will increase light reflection
– Makes it easier to locate film, etc.
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Darkroom Entrances
•
•
•
•
Single door
Double interlocking doors
Revolving door
Light-proof maze
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Pass Boxes
• Exposed/unexposed compartments
• Allow cassettes to be passed to and from the
darkroom
– Prevent light from entering during the process
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Darkroom Plans
• Processor feed tray in darkroom
– Other portions outside of darkroom for
maintenance
• Passbox/film bin/loading bench proximity
to feedtray
• Loading bench grounding
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Darkroom Plans
•
•
•
•
•
Communication system
White light and safelight switches
Ventilation
Humidification
Floor drains
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Silver Recovery Systems
•
•
•
•
•
•
Metallic replacement
Electrolytic
Chemical precipitation
Resin
Monitoring
Film
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