How much time should be spent in the darkroom before testing for darkroom fog?

• A. 5-10 minutes
• B. 15-20 minutes
• C. 25-30 minutes
• D. 45-60 minutes

Answer: (B)

Darkroom fog is caused by stray light exposing the film, so you test by leaving an unexposed film in the darkroom long enough to reveal any leakage when it’s processed. The recommended interval is fifteen to twenty minutes because that window is long enough to show even subtle fog from minor safelight leaks or small light leaks, yet short enough to fit into normal workflow. If you wait less than that, subtle fog may not become visible; waiting much longer isn’t necessary and can waste time. After this interval, develop the film as you normally would and look for a uniform, gray veil indicating fog, which would point to light leaks or safelight issues that need correction.