Processor Chemistry and Film Development
There are four steps in film development. First, the developing phase necessitates formation of the image. Then, there is the fixing phase, in this phase development is ceased and a permanent image is fixed on the film. After fixing, there is the washing phase where the residual fixer is removed (See Appendix 1). Lastly is the drying phase which involves blowing over warm air on the film (Carlton & Adler, 2012). This paper will focus on the processor chemistry and film development.
The development phase is the first stage in the processing of the radiograph. Its main objective is to convert invisible latent image into a visible form. The processing procedure is initiated by the latent image speck (see appendix 2). Arguably, the development phase is a process of chemical reduction. Such reduction is achieved by the developer as it donates to silver ions in the exposed iodide grains and silver bromide converting them to atoms of the metallic silver. The reaction equation is;
Ag+ + electron ® Ag
A change barrier around the halide grains is involved in mode of action of the developer. A negative barrier surrounds both exposed and unexposed silver bromide grains of the bromide ions produced by excess of potassium employed in the production of silver bromide during the manufacture of emulsion. (See appendix 3). This charge barrier protects the silver bromide from electron attack in the developer solution. The silver atoms act as catalyst at the latent image center as the grain can develop fully or not at all (See Appendix 4). The developer constitute of replenisher solution which consists of a solvent, developing agents, accelerators and buffers, restrainers, preservatives, hardener and a sequestering agent. The reaction involves donation of electron by a developing agent to form metallic silver by the silver ions. Appendix 5 shows the chemical reaction.
The development reaction at high volume entails bromide and acid formed (lower pH) and it is consumed as replenisher formulas have higher pH since it contains no bromide. The following is the reaction;
2AgBr + H2Q + Na2SO3
2Ag + HBr + HQSO3Na + NaBr
On the other hand, oxidation reaction wiyh low volume raises the pH and no bromide is produced during replenishment as follows;
H2Q + Na2SO3 + O2
HQSO3Na + NaOH + Na2SO4
It is noted thatfactors that affect film development phase include the type of constitutes of the developing solution, the developer temperature and time.
The fixing phase has four functions. The stage stops further development by making it more acidic, clears the image by eliminating the residual silver halide from the emulsion, fixes the image that is no longer sensitive to light and completes the process by hardening the film emulsion.
The film must be cleaned with water after development and fixing to remove all the thiosulphites complexes. Tap water is a recommended washing medium. The washing phase takes 15 seconds for a 90-seconds cycle. Otherwise, in a manual processing a minimum of 15 minutes is recommended.
The surface water is retained in the emulsion and it must be
removed. This is done through drying air of low humidity, which accelerates the
evaporation process and decreases drying time. Air temperatures of between
40-600C are used at this phase
Carlton, R. R., & Adler, A. M. (2012). Principles of radiographic imaging: an art and a science. New York: Cengage Learning.
Jenkins, D. J. (2012). Radiographic photography and imaging processes. New York : Springer Science & Business Media.