Quality Control and Darkroom Practice
Quality Control and Darkroom Practice
This domain tests processing chemistry, safelighting, fog control, and routine QC. Expect questions on developer and fixer function, temperature and time, sensitometry, and artefact recognition.
Core rules
- Manual processing: developer about 20°C for 5 minutes, fixer about 20°C for 10 minutes, with agitation. Automatic processors run near 35°C with short cycles.
- Developer converts exposed silver halide to silver; fixer dissolves unexposed halide. Contamination of developer by fixer causes low density and fog.
- Safelight must match film sensitivity, use a low-wattage bulb, and be at least 1.2 m from the bench. Test with a coin or step test.
- Replenish chemistry according to workload; monitor base-plus-fog, speed and contrast with sensitometry.
- Keep the darkroom light-tight and clean; recover silver responsibly.
Worked example
Unexposed films show uniform fog. Develop one film in total darkness: if fog persists, the developer is exhausted or contaminated. If the film clears, test the safelight by exposing a film partly covered for 2 minutes; fog under the uncovered area indicates a safelight or light leak.
Traps
- Blaming film for fog without testing safelight and chemistry.
- Using the wrong safelight filter for orthochromatic film.
- Over-replenishing or under-replenishing.
- Ignoring fixer exhaustion, which causes yellow-brown stains.