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Processing of films Definition of processingProcessing theoryDiagram
Practical processing methodsManual
Automatic
Self-developing films
Requirements for manual processingAbsolute light-tightness of the dark room
Adequate working space
Adequate ventilation
Adequate film storage facilities
Safelights
Processing equipments-tanks,
thermometers immersion, heater,
timer, film hangers
Adequate washing facilities
Manual processing cycleThe exposed film packet is unwrapped and the film clipped on to a hanger
The film is immersed in developer (at 20 degrees for 5 minutes) and agitated several times
Rinse the residual developer for 10 seconds
• Immerse the film in the fixer for 8- 10 minutes
• Wash the film under running water for 10- 20 min. to remove the residual fixer
•The film is dried in a dust – free atmosphere
Constituents of developer solutions and their functionsPhenidone- bring out the image
Hydroquinone- builds contrast
Sodium sulphite- reduces oxidation
Potassium carbonate- activates developing agents
•Benzotriazol- prevents fog
•Glutaraldehyde- hardens the emulsion
•Fungicide- prevents bacterial growth• •Buffer- maintains pH ( 7+)
•Water- solvent
Important points regarding development
The alkaline developer should be made up according to manufacturer’s instruction
Solutions should be changed every 10-14 days, irrespective of the number of films processed during that time
The recommended time is 5 minutes at 20 degrees
Fixer’s constituents and their functions
Ammonium thiosulphate- removes unsensitized crystals
Sodium sulphite- preservativeAluminium chloride- hardenerAcidic acid- maintains pHWater- solvent
Important notes regarding
fixing
Avoid contamination with developer and prepare according to manufacturer’s recommendations
Films should be fixed for double the clearing time (the time it takes to remove the unsensitized silver halide crystals)
•Films may be removed from the fixer after 2-4 minutes for wet reading but should be returned to the fixer to complete fixing
•Inadequate fixed films may appear greenish, yellow or milky and later brown
Automatic processingProcessing cycle- it is the same as for manual processing except that the rollers
squeeze off any excess developing solution before passing the film on to the fixer
Infection control measures
AdvantagesTime saving
No need for a darkroom
Standardized processing conditions
DisadvantagesStrict maintenance and regular cleaning are essential
Some models need to be plumbed in
Equipment is relatively expensive Smaller machine cannot process large extraoral films
Self-developing filmsAdvantages
- No darkroom or processing facilities are needed
- Time saving- the final radiograph is ready in about a minute
DisadvantagesPoor overall image qualityThe image deteriorates rapidly with time
There is no lead foil inside the film packet
The flexible film packet is difficult to use in positioning holders
Relatively expensive