Manual processing was performed almost exclusively prior to 1956 when Kodak began mass-producing an affordable automatic processor. Manual processing took up to an hour, some STAT exams were read "wet." Automatic processing contains several systems that work together to develop films. It functions to transform the latent image into a manifest image. This process has four components: developing, fixing, washing, and drying.
Developing
Through the use of six chemicals, the developer solution converts exposed silver (latent image) to black metallic silver. The reducing (developing) agents can only function in an alkaline environment. The rate of reduction from silver to black metallic silver is increased due to the source of electrons supplied by the developing agents, in addition to the electrons supplied by the bromine and iodine on the surface of the matrix. The electrons are provided to neutralize the sensitivity speck. Time is critical; if films stay to long, or not long enough in the developer solution, proper development is not possible. Temperature is also critical; high or low developer temperature results in over or under active developing agents which affects film density. It is very important that the developer not get contaminated the by the fixer.
The activator chemical provides an alkaline environment that causes the emulsion to swell. The reducing agents create the density on the film. The preservative chemical reacts with oxygen in air in order to prevent oxidation of developing agents. The solvent chemical is used to dilute the concentration of chemicals to the proper strength. The solvent should be filtered and treated to prevent algae. The hardener chemical controls emulsion swelling to prohibit roller transportation problems. Finally, the restrainer chemical―also referred to as starter solution―restrains the developing agents by preventing them from developing unexposed silver crystals.
Fixing
The purpose of the fixer solution is to stop the developing process. There are five chemicals in the fixer solution. The clearing (fixing) agents can only function in an acid environment; it removes the unexposed, undeveloped silver halide crystals from the emulsion.
The activator chemical provides the needed acidic environment. First, the clearing agent removes the unexposed, undeveloped SHCs. The preservative chemical prolongs the effective life of the solution by dissolving the silver from the solution allowing the clearing agent to remove silver from the emulsion. As a result of the large amount of silver in the fixer solution, a silver recovery unit is needed to remove it. The solvent chemical is used to dilute the concentration of chemicals to the proper strength. The solvent chemical should be filtered and treated to prevent algae. Finally, the hardener chemical shrinks and re-hardens the emulsion.
Washing
The washing component provides the task of removing chemicals form the film emulsion which is required for good archival film quality. Residual chemicals left in the emulsion will cause the film to discolor (yellow). Agitation during the washing process aides in removing chemicals. It is important that the wash tank has a fresh supply of water. The tank should be drained when not in use to prevent growth of algae.
Drying
The drying component dries the film for interpretation and storage by blowing warm, dry air over its surface.
Transport
The transport system functions to move the film through the different processing steps (developing, fixing, washing, and drying) by means of rollers, gears, chains, and sprockets. The rollers serve to agitate the solution against the film surface. There are three roller subsystems: transport racks, crossover networks, and the drive system.
Transport racks are found inside the tanks and function to move film through the tank. Turnaround assemblies (master roller, guide shoes) located at the bottom of the solution tanks function to redirect the film up towards the top of the tank to the crossover rollers and are.
The crossover networks located at the top of the solution tanks serve to direct the film from one processor solution to the next and to perform a squeegee action on the film. Crossover rollers should be cleaned after the processor has not been in use for a while (i.e. overnight). Entrance rollers―also part of the crossover network―directs the film from the feed tray into the developer tank.
The drive system controls the speed at which the films travel through the processor solution tanks. The film should travel through the developing solution at 22 seconds; the fixer solution at 22 seconds; the wash solution at 20 seconds; and the dryer at 26 seconds.
A film failing to travel through the transport system can result from too rapid film feeding (overlapping films); broken drive gears; and warped or improperly seated roller racks or guide shoes.
Replenishment
The replenishment system is responsible for maintaining proper solution concentration (developer, fixer, and water) to the tanks during the processing cycle. The emulsion in the film carries solution as films pass from one tank to the next, which depletes the solution. If the solution level drops, the density and contrast of the film will be affected. There are two types of replenishment systems: volume and flood. In a volume replenishment system, solutions are replenished only while film is being feed into processor and in a flood replenishment system, solutions are replenished at certain time intervals.
Temperature Regulation
The temperature regulation system functions to control the temperature of each section of the processor. Maintaining proper developer temperature is very critical; it is controlled by a thermostat and it must be maintained between 92° and 96° F. Developer temperature shouldn't vary more than ± 5°. Developer is circulated through a circulation coil in the bottom of the fixer and wash tanks, thereby regulating the fixer temperature by heat conduction. Fixer solution temperature is not as critical as developer, it is usually slightly lower temperature. Wash solution is kept about 5º F lower than the developer.
Recirculation
After the replenishment system adds solution to the tanks, the recirculation system provides agitation to the solution. This agitation provides uniform concentration and temperature to the solution and prevents air bubbles from clinging to the film. It keeps the fresh solution in contact with the film emulsion and it filters debris, such as gelatin particles, from the solution. In addition, this system circulates 1-2 gallons of fresh water every minute in the wash tank. The replenishment system adds fresh chemicals to the top of the tank and the recirculation system draws solution from the bottom of the tank and replaces it on the side of the tank.
Dryer
The dryer system functions to remove water from the film by blowing warm, dry air (120º to 130º F) over its surface. Squeegee crossover rollers remove water from the wash tank and heated air is blown through a series of tubes that surround both sides of the film.
Silver Recovery
About half of the silver in the emulsion remains in the fixer tank after the film is processed. A drain in the fixer tank is connected to a silver recovery unit where the excess silver is removed. Silvery recovery is only slightly desirable for financial reasons, the collected silver is a very, very, very small source of income to the department. More importantly, silvery recovery is necessary for ecologic reasons. Fixer silver is toxic to the water supply and we have little choice but to remove the silver before we dump the exhausted fixer down the drain.
There are three types of silvery recovery units, metallic displacement, precipitate, and electrolytic. With the metallic displacement unit, fixer enters a metallic displacement cartridge and metallic silver is precipitated onto steel wool within. With the precipitate unit, the tank is filled with a chemical (i.e. sodium borohydride) which causes metallic silver falls to the bottom and form a sludge. The electrolytic method (see diagram) is the most common type in use. In this unit, fixer solution passes through an electric current causing silver to be plated onto the cathode cylinder of the unit. The silver is periodically removed by scraping it from the stainless steel cathode.
When an automatic processor is started up at the beginning of the day, or restarted after an extended standby period, the technologist should process an unexposed and undeveloped 14 × 17 inch film. The processor lid should be kept ajar when not in use to prevent cross contamination caused by fumes from solutions. There should also be covers on the developer and fixer tanks.
The rollers in the tanks should be cleaned to prevent build up of chemical deposits, dirt, algae, and emulsion. Crossover rollers should be cleaned daily and the roller racks should be cleaned monthly. If the rollers are not properly maintained, a buildup of chemicals can cause a roller misalignment and result in films being scratched the film as they pass by. The crossover rollers must be removed carefully so as to not mix chemicals between tanks. The fixer solution must never be spilled into the developer solution. The tanks drained and washed monthly usually by a processor service company.
Sensitometry should be done on a general processor on a periodic basis and must be done on a mammography processor daily. The purpose of sensitometry is to measure the characteristic responses of film to exposure and processing. Sensitometry is performed by using a sensitometer and a densitometer. A sensitometer―a device with a controlled intensity of light that is used to expose an optical step wedge of either 11 or 21 steps (densities) onto a film―is exposed onto a film and developed in the automatic processor being tested. A densitometer is a device with a calibrated light source that is used to measure the optical densities (OD) of the exposure on the film. Once the sensitometry film has been exposed and developed, a densitometer is used to measure the density on the film and thus the perfor mance of the processor.