For archival storage, how much fixer solution is required?

• A. Less than 1 mg/cm2
• B. No restriction
• C. Less than 2 mg/cm2 of retained thiosulfate
• D. At least 5 mg

Answer: (C)

Archival storage depends on keeping fixer residues to a minimum, because leftover thiosulfate can continue to affect the emulsion over time, causing image degradation such as fogging or discoloration and weakening the film’s long‑term stability. The established limit is that no more than about 2 mg of retained thiosulfate per square centimeter of film surface should remain after washing. This threshold strikes a practical balance between effective cleaning and feasible processing, ensuring the radiograph remains stable over extended storage. If residues were higher, additional washing or reprocessing would be needed to bring the film into a safe range.