For film archival, thiosulfate levels calculated from fixer retention testing should be how many mg/cm²?

For film archival, the correct amount of thiosulfate levels calculated from fixer retention testing should be 2 mg/cm². This standard is based on industry guidelines that aim to minimize the potential for photographic materials to degrade over time.

Thiosulfate is a chemical used in the fixing process of film that helps to remove unexposed silver halides. Retaining excessive amounts of thiosulfate can lead to the deterioration of the film, causing fading or discoloration, which compromises the archival quality of the images. By maintaining thiosulfate levels at or below 2 mg/cm², it ensures that the film achieves an optimal balance between image permanence and chemical stability, thus preserving the integrity of the photographic materials for historical documentation or future reference.

The other levels presented in the choices represent higher thresholds, which could lead to higher risks of film degradation, making 2 mg/cm² the most appropriate value for ensuring long-term archival quality.