ISO 18917:1999

Overview

ISO 18917:1999 specifies analytical test methods for the determination of residual thiosulfate and related chemical residues in processed photographic materials. It covers silver halide/gelatin products that have undergone a final thiosulfate fixing bath followed by a water wash and provides three primary test procedures: iodine‑amylose, methylene blue, and silver sulfide (silver densitometric) methods. Results from these methods can, within stated limitations, correlate with the image stability of processed photographs.

Key topics and technical requirements

• Scope and exclusions
  • Applies to silver halide/gelatin films, plates and papers processed with a thiosulfate fixer and water wash.
  • Excludes stabilised black‑and‑white products, thermally processed films, and instant-type products.
• Three standard methods
  • Iodine‑amylose method: Measures thiosulfate ions; suitable for fibre-based paper, resin-coated paper, films and plates - specifically recommended for materials containing incorporated developing agents. Analytical range cited: 0.002–0.40 mg/cm².
  • Methylene blue method: Also measures thiosulfate; usable with films and papers but not for materials with incorporated developing agents.
  • Silver sulfide (densitometric) method: Detects thiosulfates, polythionates and other residual chemicals that react with silver ion to produce a silver “stain” under test conditions.
• Sampling notes
  • Materials with photosensitive layers on both sides (or with gelatin backing) may retain roughly twice the thiosulfate of single-sided coatings; reporting guidance is provided in the standard (see annexes and examples).
• General laboratory requirements
  • Use of certified reagent‑grade chemicals, distilled (or equivalent) water, and appropriate glassware (heat‑resistant borosilicate). Instrumentation includes spectrometers/photometers, pH meters and standard lab apparatus.
  • Safety and hazard warnings are specified; proper PPE and handling procedures required.

Applications and who uses it

• Quality control in photographic film and paper manufacturing
• Analytical labs assessing wash adequacy and predicting image permanence
• Conservation scientists and archives evaluating processed photographic collections
• Forensic and research labs that require quantitative residual chemical data for processed silver‑halide materials

The standard helps link residual chemical levels to potential image degradation (stain, density loss) and supports decisions on processing, washing protocols and archival treatments.

Related standards

• ISO 3897, ISO 5466, ISO 6051, ISO 10602 (storage and archival guidance referenced)
• Normative references within ISO 18917: ISO 5‑3 (density measurements), ISO 10349‑1 (photographic‑grade chemicals)
• Informative annexes A–D provide guidance on keeping characteristics, method selection and reagent preparation.

Keywords: ISO 18917, residual thiosulfate, iodine‑amylose, methylene blue, silver sulfide, processed photographic materials, silver halide, fixing bath, image stability, photographic testing.