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Essential Guide to Darkroom Printing
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On one side of the darkroom there should be a dry workbench for films, clean film hangers, film boxes and cassettes. The hands must be dry when working at this bench. It contains an area for loading and unloading film holders, a cassette transfer cabinet, a film bin, compartments for cassettes and exposure holders, storage for hangers, a wastepaper receptacle, and storage for processing materials. Loading Area.
Guide to Darkroom Printing: Equipment Needed
The length of the loading bench depends on the volume of work and the space available. The minimum length of the working surface should accommodate two 14 by inch cassettes, side by side, to permit unloading and reloading of two cassettes. Preferably, it should be long enough to accommodate at least four 14 by inch cassettes, side by side, to preclude piling of cassettes. The working surfaces shown in figure require approximately 96 inches, exclusive of transfer cabinet and dryer space.
The bench should be about 36 inches high and 24 inches deep.
A strip of one- half by one-inch molding placed lengthwise and six inches from the back edge of the bench anchors the cassettes while they are being opened and closed and keeps them at the front of the bench within the working area of maximum efficiency. Unloading the cassette: Under safelights, the cassette is placed face downwards on the bench and the locking clip is released. The cassette is then turned over and the front of the cassette is tipped so that the film falls from the cassette well. The film is removed with the dry hand and the cassette closed. Loading the cassettes: Under safelights the cassette is placed face downwards on the bench and as before opened from the back.
The unexposed film, lightly gripped at its edge is lowered gently into the cassette well.
The Darkroom Cookbook | ScienceDirect
The cassette is closed by bringing over the back and engaging the locking lip. Darkroom illumination: This may be considered under two headings: 1. Safelighting While all film materials would instantly be fogged if exposed to white light, safelighting which is the use of dim colored lighting provides sufficient illumination by which one can handle, manipulate and process film. Providing exposure to such lighting is brief, no significant fogging will occur. But it is to be noted that no safelighting is completely safe; all films will become significantly fogged if exposed to safelights for ling enough.
Darkroom Dynamics, 2nd Edition
The radiographic intensifying screen emits light, which exposes the radiographic film placed between the two screens. The emulsion of x- ray films must be chemically processed to render visible and permanent the information recorded in the latent image. Processing causes the silver ions in the silver halide crystals that have been exposed to light to be converted into microscopic black grains of silver. The processing sequence comprises the following steps: wetting, developing, rinsing in stop bath, fixing, washing and drying. These processing steps are completed in an automatic processor.
Film processing involves a number of complex chemical reactions whose activity and efficiency are influenced by various factors including temperature and pH of the chemical environment in which the reactions take place. Before the introduction of automatic film processing, x-ray films were processed manually. All radiographic processing is automatic today. The chemicals involved in both are basically the same.
In automatic processing, the time for each step is shorter and the chemical concentration and temperature is higher. Processing the film magnifies this action many times until all the silver ions in exposed crystals are converted to atomic silver, thus converting the latent image into a visible radiographic image. The exposed crystal becomes a black grain that is visible microscopically.
Processing is as important as technique and positioning in preparing a quality radiograph. A change in recommended processing conditions should never be a substitute for a poor radiographic exposure because the result is always a higher patient dose. Bushong S. In automatic processing, this step is omitted and the wetting agent is incorporated into second step, developing. The developing stage is very short and highly critical. After developing, the film is rinsed in an acid solution designed to stop the developing process and remove excess developer chemicals from the emulsion.
Photographers call this step the stop bath. In radiographic processing, the stop bath is included in the next step, fixing. The gelatin portion of the emulsion is hardened at the same time to increase its structural soundness.
Fixing is followed by vigorous washing of the film to remove any remaining chemicals from the previous processing steps. Finally the film is dried to remove the water used to wash it and to make the film acceptable for handling and viewing. Developing, fixing and washing are important steps in the processing of radiographic film. The precise chemical reactions involved in these steps are not completely understood. However a review of the general action is in order because of the importance of processing in a high quality radiograph.
Event Purpose Approximate time Manual automatic Wetting Swells the emulsion to permit subsequent chemical penetration 15s Development Produces a visible image from the latent image 5 min 22s Rinsing in stop bath Terminates development and removes excess chemical from the emulsion 30s Fixing Removes remaining silver halide from emulsion and hardens gelatin 15 min 22s Washing Removes excess chemicals 20 min 20s Drying Removes water and prepares radiograph for viewing 30 min 26s 4.
The wetting agent is water and it penetrates the gelatin of the emulsion causing it to swell. In automatic processing the wetting agent is in the developer. Its primary purpose is to convert into visible form, the invisible latent image produced when the film was exposed. During development the silver halide grains in the emulsion which were affected by exposure are reduced to metallic silver while those which were unaffected remain largely unchanged.
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Chemical action of developer: Development is a process of chemical reduction. The reduction is achieved by the developer donating electrons to the silver ions in the exposed silver bromide grains, converting them to atoms of metallic silver. Component Chemical Functions Developing agent Phenidone Hydroquinone Reducing agent; produces shades of gray rapidly Reducing agent; produces black tones slowly Activator Sodium carbonate Helps swell gelatin; produces alkalinity; controls pH Restrainer Potassium bromide Antifog agent; protects unexposed crystals Preservative Sodium sulfite Controls oxidation 5.
Hardener Glutaraldehyde Controls emulsion swelling and enhances archival quality Sequestering agent Chelates Removes metallic impurities; stabilizes developing agent Solvent Water Dissolves chemical for use Bushong, S. It is the developing solution used in greatest quantities in x-ray departments today. Developer replenisher consists of: 1. Solvent: water is the solvent used in radiographic processing.
It acts as carrying medium in which the developer constituents are dissolved. It has a softening effect on the film emulsion gelatin, thus allowing the chemicals tio penetrate the emulsion and act on silver halides.