How often should the darkroom fog be tested?

• A. Monthly
• B. Annually
• C. Semi-annually
• D. Weekly

Answer: (C)

Darkroom fog is unwanted film exposure caused by stray light or changes in the processing environment, which shows up as extra density on a developed film. The test checks that the safelight and darkroom conditions aren’t fogging the film, by placing a film in the darkroom under safelight for a set time, developing it, and measuring the resulting density. If the density is higher than an acceptable baseline, you’ve got a fog issue from the safelight or room seals, indicating a problem to fix (bulb wattage, distance, filter, door seals, etc.).

Testing every six months keeps surveillance on the darkroom’s condition without excessive workload. Fog risks tend to evolve slowly, so semi-annual checks commonly strike a practical balance between catching gradual degradation and not over-testing. If a darkroom has just been set up, had changes like a safelight replacement, or shows signs of trouble, more frequent checks are reasonable, but routine practice targets a semi-annual schedule.