FILM PROCESSING

FILM PROCESSING 

Film processing involves a series of organised procedures,namely, development,rinsing,fixing,washing and drying

DEVELOPING 

Development is chemical process that produces visible image from latent image. The solution used for this purpose this is called developer. The developer converts the exposed silver into metalic silver,by reduction process.

          

    The developer contains,developing agent,activator,restrainer,preservative,hardener,sequestring agent and solvent. Hydroquinone,phenidone or metol are used as developing agents.Hydroquinone is a reducing agent,slow acting and is resposible for the black shades.Penidone is a reducing agent,acts rapidly and producec lighter gray shades.phenidone controls the toe of the curve and hydroquinone controls the shoulder of the curve.

       

        Sodium carbonate and sodium hydroxide serve as an activator,which swells gelatin,produce alklinity and control the p H. Thus it enhances the action of the developer. Pottassium bromide is used as restrainer ,which is antifog agent. Itdecreses the fog, by protecting the unexposed crystals.Fog is the development of unexposed silver halide grains, that do not contains the latent image. Thus the restrainer, restrict the action of the developing agents only to those exposed AgBr crystals.

        Sodium sulfite is used as preservative.The preservative control the oxidation of the developing agent,by air,thereby increasing the life of the developer. Hydroquinone is more sensitive for aerial oxidation. Preservative helps to maintain proper development rate and also maintains balance amoung developer components.The oxidation products, of the developing agents decompose the alkaline solution and form colored materials that can stain the emulsion.The preservative dissolves these oxidation products and form colorless sulfonates.

        Hardener and sequestring agents are used in automatic processores. Glutaraldehyde acts as hardener, to control emulsion swelling and softening. Chelates is used as sequestring agent. Which remove metal impurities ansd slouble salts.Water is used as solvent to dissolve the chemicals

RINSING

When the X-ray film is removed from the developer.it should be rinsed , in order to remove the soluble chemicals and oxidation products.Rinising also partially stops the reaction of the developer and neutrilizes the alkalinity of the rsidual developer. Thus, it reduces fog formation  Rinsing is done with done with water. Insufficient rinsing will shorten the fixer life and also destroys its hardening action.

FIXING

Fixing removes the unexposed silver halides without damaging the image.hardens the gelatin emulsion and stops rsidual development.

        The fixing solution consists ofactivator,fixingagent,hardener,preservative,buffer,sequestring agent, and solvent. Acetic acid is used as activator, which neutralizes the developer and stops its action. Sodium thiosulfate or ammonium thiosulfate salts are used as fixing agents. It dissolves the unexposed, undeveloped silver halides, leaving the deveolped metallic silver . Excess hypo may cause oxidation and make image disclosure to brown, over a period of time. Silver combine with hypo and forms silver sulfide, which appear yellowish brown.

        Pottasium alum used as hardner. It hardnes the gelatin emulsion, therby protecting it form physical injuries.When the undeveloped silver brimode is removed from the film, the emulsion starts shrinking.The hardener enhances the shrinking process, and makes the emulsion too hard. Now, its is suitable for transport through washing and drying.

         Sodium sulfite is used as preservative , which maintains the chemical balance. The developer may mix with fixer solution and may cause chemical imbalance .Thus ,preservative protects the fixing agent from decomposition .Acetate is used as buffer, which keep the pH of the fixer as constant. Boric acid and boric salts are used as sequestring agent, which removes metallic ions, sucjh as aluminum impurities.The water is usually used as solvent. It helps to mix the chemicals.

WASHING

After fixing, the film must be washed with water, to remove fixing bath chemicals, especially hypo. Otherwise , it will change the black silver to brown silver sulfide.Washing require runnnig water and it takes about 20 minutes. Incomplete washing permits the hyporetention,which may cause image fading, and make the film brown with age .The temperature of the water must be maintained at 3 degree in automatic processor.

DRYING

The final step in processing is to dry the radiograph. The film may be dried in dust  free open air area, where the temperature is less than 35 degree.  Hot air drying cabinets are also useful for drying , which is eqiupped with a fan and heating element to flow hot air.Wetting agents such as photo-flo or alchol used to decrease the time drying time.In automatic processor,wram dry air is blown over both surfaces of the film, while it is moving in the drying cabinet.