Creating the Image Unit III

Film Processing Chapter 20

Objectives Explain process of film developing and fixing Describe synergistic properties of automatic processor reducing agents Identify primary chemical and its function for each developer and fixer agents

Objectives Explain washing and drying processes of film archiving Describe functions of subsystems of automatic processor

Objectives Discuss basic function of radiographic darkroom design and safelights Explain rationale for use of silver recovery system

Purpose of Film Processing To accumulate enough black metallic silver at sensitivity specks to yield visible film image Due to predominance of digital imaging, very little chemical processing still done in developing nations

Purpose of Film Processing Film processing involves four steps: Developing Fixing Washing Drying

Developing First step in wet processing Results in visibility of silver at latent image sites

Developing Consists of: Reducing (primary) agents Activator Restrainer Preservative Hardener Solvent

Reducing Agents Provide free electrons to silver ions Through “gates” of exposed sensitivity specks Reduction/oxidation

Reducing Agents Two reducing agents work synergistically Phenidone (P developer) Works quickly to produce shades of gray

Reducing Agents Two reducing agents work synergistically Hydroquinone (Q developer) Works slowly to produce black areas

Reducing Agents Used developer becomes oxidized If not properly replenished, changes color from deep amber to brown to rust-red

Activator Typically sodium carbonate Added to developer to maintain alkaline pH Helps reducing agents get to silver halides Swells gelatin Making it easier to penetrate

Activator Makes developer solution caustic Should wear rubber gloves and apron Neutralize spills with fixer or dilute with water

Restrainer Typically potassium bromide Provides distraction to overactive reducers Prevents developer from acting on unexposed silver halide crystals

Preservative Developer easily oxidized by air Sodium sulfite decreases this oxidation process Careful tank design can reduce developer’s exposure to air

Hardener Glutaraldehyde Controls swelling of gelatin Prevents abrasions during processing Maintains uniform film thickness

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

Hardener Too much hardener will harden emulsion too soon Prevents chemical interactions from happening Traps moisture in gelatin

Solvent Water Should be filtered In tropical areas 5-10 micrometer filter In tropical areas Should be treated for bacteria and fungi

Contamination Developer impacted by contamination 0.1% of fixer present in developer will stop action of reducers Results in gray, low-contrast films Developer carried into fixer tank routinely Thus, developer does not contaminate fixer

Contamination Can be avoided by using splash guards When cleaning processor: Fixer tank should be filled Developer tank should be cleaned

Contamination When shutting down processor: Lid should be opened Prevents fixer condensation from dripping into developer tank

Fixing Undeveloped silver halides must be removed from film

Fixing Consists of: Clearing (primary) agent Activator Preservative Hardener Solvent

Clearing Agent Usually ammonium thiosulfate Bonds with unexposed silver halides Becomes ammonium thiosilversulfate

Clearing Agent Films will appear milky if not properly cleared Typical clearing time: 15-20 seconds Manual processing: 2-3 minutes

Activator Acetic acid maintains acidic pH Enhances function of clearing agents Neutralizes developer solution Stops action of reducers

Preservative Sodium sulfite Removes silver from ammonium thiosilversulfate Allows ammonium thiosulfate to continue to remove silver halides

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

Solvent Filtered and treated water

Depletion Fixer eventually becomes silver saturated Clearing time gets longer Replenishment prevents depletion Silver recovery removes silver from used fixer solution

Washing Water removes as much chemistry as possible Temperature should be 5º F (3º C) lower than other solutions If too cool, emulsion will reticulate Film will have crackled appearance

Washing If fixer not washed from film: Proper washing requires: Film becomes yellow and then brown with age Proper washing requires: Agitation Enough time

Washing Wash tanks prone to algae and bacteria growth Tank should be drained when processor shut down

Drying Accomplished by forcing hot air over both sides of film 120-150º F (43-65º C) Hardens emulsion and seals supercoat

Storage 70º F (23º C) and 60% humidity Length of storage dependent on state law and institution Usually 5-7 years Minor and legal cases indefinite Mammograms

Automatic Processors First introduced by Kodak (1957) Utilizes sub-systems: Transport Dryer Replenishment Circulation Temperature control

Transport System Moves film through developer, fixer, washer, and dryer sections Controls length of time radiograph is immersed in each solution Agitates chemistry

Dryer System Final stage of processing Squeegee crossover rollers Removes excess water Blows hot air through slotted tubes Film emulsion shrinks and seals

Replenishment System Replaces chemicals as they are depleted Two types of replenishment: Volume Flood

Replenishment Rates 4-5 ml of developer/inch of film 6-8 ml of fixer/inch of film

Mixing Solutions Must be done according to manufacturers’ specifications Starter solution Acetic acid and potassium bromide Must be added to fresh developer chemistry

Developer Starting and Seasoning Adequate mixing of developer chemistry necessary Requires running processor for 15-20 minutes prior to processing films

Processor Solution Safety Hazardous materials Occupational Safety and Health Administration (OSHA) U.S. Environmental Protection Agency (EPA)

Processor Solution Safety Material Safety Data Sheet (MSDS) Protective eyewear/eyewash Rubber gloves and apron

Circulation System Stabilizes temperature Agitates and mixes chemistry Filters solutions

Temperature Control System Maintains all three solutions at compatible temperatures

Darkroom Safelights Entrance Pass box Ventilation

Darkroom Safelights Kodak GBX filter Dark red Low intensity (7-15 watts) 4 feet from work area Direct illumination possible with most films

Darkroom Safelights Kodak Wratten Series 6B Orange-brown Amber filter Safe for films sensitive to blue/violet light

Darkroom Safelights Light emitting diode (LED) High initial cost Long-lasting

Darkroom 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.

Darkroom Entrances Single door Double interlocking doors Revolving door Light-proof maze

Darkroom Pass Boxes Exposed/unexposed compartments Allow cassettes to be passed to and from darkroom Prevent light from entering during process

Darkroom Ventilation Chemical fumes must be vented to outside of building

Silver Recovery Systems Feasible from financial standpoint Prevents toxic heavy metal pollution in environment

Silver Recovery Systems Must adhere to legislative acts: Water Control Act of 1972 Hazardous Waste Act of 1976 Clean Water Act of 1984 Conservation and Recovery Act of 1986