1. Processing of films Definition of processing Processing theory Diagram

2. Practical processing methods Manual Automatic Self-developing films

3. Requirements for manual processing Absolute light-tightness of the dark room Adequate working space Adequate ventilation Adequate film storage facilities

4. Safelights Processing equipments-tanks, thermometers immersion, heater, timer, film hangers Adequate washing facilities

5. Manual processing cycle The 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

6. 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

7. Constituents of developer solutions and their functions Phenidone- bring out the image Hydroquinone- builds contrast Sodium sulphite- reduces oxidation Potassium carbonate- activates developing agents

8. Benzotriazol- prevents fog Glutaraldehyde- hardens the emulsion Fungicide- prevents bacterial growth Buffer- maintains pH ( 7+) Water- solvent

9. 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

10. Fixer’s constituents and their functions Ammonium thiosulphate- removes unsensitized crystals Sodium sulphite- preservative Aluminium chloride- hardener Acidic acid- maintains pH Water- solvent

11. 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)

12. 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

13. Automatic processing Processing 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

14. Advantages Time saving No need for a darkroom Standardized processing conditions

15. Disadvantages Strict maintenance and regular cleaning are essential Some models need to be plumbed in Equipment is relatively expensive Smaller machine cannot process large extraoral films

16. Self-developing films Advantages - No darkroom or processing facilities are needed - Time saving- the final radiograph is ready in about a minute

17. Disadvantages Poor overall image quality The 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