How big should the washer tank be compared to the developer tank?

• A. 2x
• B. 3x
• C. 5x
• D. 4x

Answer: (D)

Focus on how washing works in film development. After the film is developed, residual chemicals need to be carried away by fresh water. If the wash bath is too small, the water becomes quickly saturated with developer, so the concentration gradient that drives diffusion from the film into the wash drops and residues aren’t removed effectively. Having a washer tank about four times the volume of the developer tank gives ample dilution and rapid turnover of wash water, promoting thorough rinsing of all residues. Good agitation and regular changes of the wash water further improve cleaning, but the critical point is providing enough bath volume for effective rinsing. Hence, four times the volume is the typical guideline.