what is manual x-ray film processing in darkroom?
The manual film processing is the process which help to convert the latent images to visible images by the help of chemical agents. This method always done in darkroom at under the safe light.
There are following staps are involved in manual film processing.
1) Developing.
2) Rinsing.
3) Fixing.
4) Washing.
5) Drying.
1) Developing:- The development of a radiographic film is a chemical process which convert the latent images into visible images. This process reduce x-ray exposed silver bromide of x-ray film into plain film. Thus action of the developer is sensitive.
The developing time is about 3-5 min about 68-72 degree F, depending on fresh of the developer solution. The developer solution contains:-
a) Developing agents:- The developing agents contain Hydroquinone and Metol. The Hydroquinone is a reducing agent which is slow acting so it is responsible for the black shades of image. But Metol are acts repidly and produces lighter shades of gray. Thus Metol gives fine details.
b) Activator:- In activator, sodium carbonate and sodium hydroxide are used to swell the emulsion. These chemical are produce alkalinity, control the PH and making easier penetration of developing agents in to emulsion
c) Restrainer:- In Restrainer, potassium bromide and potassium iodide are used. These are antifogging agents. These compounds are decrease the fog, by protecting the unexposed crystal.
d) Preservative:- In preservative, Sodium sulfite used. The sodium sulfite control the oxidation of the developing agent by air so it increases the life of developing agent. Preservative helps to maintain proper development rate and also maintain balance among developer components.
2) Rinsing:- Rinsing is the next step after developing. This is done to remove the excess of developer retained on the surface of x-ray film. The alkaline developing solution is prevented from reaching the fixer tank, other wise the acidic nature of the fixer will be neutralised. Rising is done for 30 second in cool water. we add 28% acetic acid to rinser water to help prolong the life of fixer solution.
3) Fixing:- It is a process of making the image permanent without fading.
In this chemical process, the undeveloped silver bromide is removed from the film and precipitation into the solution by the clearing agent in the fixer
The fixing solution are given below
a) Fixing agent:- In fixing agents, sodium thiosulfate or ammonium thiosulfate (Hypo) salts are used . Sodium thiosulfate Ammonium thiosulfate (Hypo) are used as fixing agent. It dissolves the unexposed, undeveloped silver halides, leaving the developer metallic silver.
b) Preservative:- sodium sulfite is used in preservative. It maintain the chemical balance. Thus preservative protect the fixing agents from decomposition.
c) Hardener:- Chrome alum or potassium alym are used in Hardener. these are protected film by scratch.
d) Activator:- Acetic acid is use as activator whice neutralize the developer and stops it’s action.
4) Washing:- Washing is the next step of processing after of fixing. The film most be washed with cool water to remove the all chemical agents on the film because it will change the black silver to brown silver sulfide. The film after fixing needs washing in the tank for 10-20 minutes for best results. The washing time is prolong if fixing solution is an exhausted one because here more silver salts remain on the film. The temperature of washing water shall be between the 65-75 degree F.
5) Drying:- After washing the film must be dried safely without blistering or bending. The water shall be drained off fully, from the film after the washing is over. The drying temperature must not exceed 35 degree C.
Drying methods are given below:-
a) By handing them individually with the help of a safety pin on to a rope wire in a a dust free room with fans.
b) By use of drying cabinets which are equipped with a heater and fan in it.
c) By using alcohol (70%) bath for 2 minutes which selectively remove the water from the film and helps faster drying.
d) Photo Flo solution method.
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