Film processing 2

Processing cycle Dev. Rinse Fix Wash Dryer

Developing Dev

Rinsing (stop bath) Rinse

Rinsing in manual processing Immediately after development the film is dipped in the water in order to: Stop development To wash the developer from the surface of the film – (reduces developer carry over to fixer)

Rinsing in Automatic processing? No rinsing stage The developer is removed from the film surface by passing it through the special type of rollers called “squeegee rollers” Alkaline Developer is neutralized by the acid in the fixer

Fixing Film Film Fixer

Functions of fixing To stop any further development Clears the image (making the background transparent to light) Makes the image permanent (fixed) (no more sensitive to light) by Removing the undeveloped silver bromide crystals from the emulsion Hardens the emulsion

Fixer constituents Solvent Fixing agent Acid Hardener Buffer Preservative Anti-sludging agent

Functions of fixer constituents Solvent (water) Carrying medium for the active ingredients Controls the acidity by diluting Fixing agent (Sodium Thiosulphate /Ammonium Thiosulphate Combines with insoluble AgBr to form soluble compounds (Ammonium Argento-Thiosulphate & NH4Br

Acid (Acetic acid – pH 4.0 – 4.5) To stop development To provide suitable working environment for hardening agents Hardener (Aluminium chloride & aluminium sulphate) Hardens the emulsion to limit water absorption, to reduce drying time, to minimize physical damage

Buffer (Sodium acetate & acetic acid) Controls the pH in a precise range in order to: i. Prevent sulphurization ii. Neutralize the developer iii. Optimum hardening Preservative (Sodium sulphite) Retards the decomposition of thiosulphate and delays the onset of sulphurization Anti-sludging agent (Boric acid) Reduces the formation of sludge of insoluble aluminium compounds by the aluminium salts used as the hardner

Factors affecting Fixation The quality and quantity of fixation depends on the: Constitution and activity of fixing solution Fixer temperature Fixing time

Constitution & activity of fixing solution At a given temperature the activity of fixer solution depends on: Fixing agent Concentration of fixing agent Amount of hardener present The amount of soluble silver compounds and soluble halides present pH pH does not affect clearing action directly, but reduces the function of hardeners if becomes high

Fixer temperature The activity of fixing agents increases with temperature. But high temperatures cause emulsion swelling and becomes susceptible to damage. However precise control of temperature is not necessary

Fixing time The fixing time should be long enough to complete the fixing process. The required time for complete fixation depends on the i. activity i. type of film emulsion iii. Agitation of fixer solution Manual processing may be as long as 5 minutes Automatic processing :- 15 sec in a 90 sec cycle.

Replenishment of Fixer Replenishment of fixer is necessary to Maintain the activity Maintain the volume The rate of replenishment depends on Area/number of films processed Type of emulsion/film Type of image

Replenishment of chemicals Automatic processing Added automatically by the replenishment pumps at a given rate for each film processed Manual processing Suitable quantity is added manually at regular intervals

Washing Removes the fixing solution contaminated with silver complexes and ammonium halides from the film surface and from film emulsion Running water is used to maintain a concentration gradient and to improve the diffusion rate of chemicals from the emulsion to water If not washed properly the emulsion will gradually acquire a yellow-brown sulphur stain during storage

Factors affecting washing efficiency Type of film emulsion Condition of fixing solution Condition of water Agitation of water Temperature of water Washing time Thiosulphate level of < 3 microgram/square cm is recomended 100% efficiency is not practicable. The washing time is selected so that the film will not be stained within 10 years of storage

Drying Removes all of the surface water and most of the water retained in the emulsion Manual processing:- Keep the film in a drying cabinet in which hot air is circulated. Takes about 10-15 minutes Automatic Processing:- Surface water is removed by squeegee rollers ; evaporation removes the emulsion water. 25 sec in a 90 sec cycle

Factors affecting drying time & efficiency The wetness of the emulsion; governed by: i. hardness of the emulsion ii. emulsion thickness The drying conditions; governed by: i. Air humidity ii. Air Temperature iii. Air circulation – rate of change

Summary If a film is not processed properly the whole effort made in the x-ray room or in the ward to obtain a good radiograph will be lost It is essential to pay similar attention to film processing as you pay at the x-ray room or in the ward when taking the x-ray