How long should you spend in the darkroom before checking for darkroom fog?

• A. 10-15 minutes
• B. 15-20 minutes
• C. 20-30 minutes
• D. 5-10 minutes

Answer: (B)

The test checks for darkroom fog by letting an unexposed film sit in the darkroom under the safelight for a set period and then processing it. If the safelight or the room leaks light, or there are other fog sources, the film will show a uniform gray fog after processing. The 15-20 minute window is used because it’s long enough for even low levels of stray light or mild fogging to become visible on an unexposed film, yet not so long that normal storage changes or accidental exposure confuse the result. This interval provides a practical, reliable check: if the film remains clear after processing, the darkroom conditions are acceptable; if fog is present, inspect safelight distance, wattage, shielding, and door seals, then re-test.