Overview
ISO 10636:1994 is an international standard specifying the purity requirements and test methods for anhydrous sodium thiosulfate and sodium thiosulfate pentahydrate used as processing chemicals in photography. Developed by ISO Technical Committee 42 (Photography), this standard ensures photographic-grade chemicals meet critical chemical and physical criteria to maintain image quality and processing reliability.
The standard defines limits for impurities such as insoluble matter, heavy metals, iron, alkalinity, acidity, sulfide content, and specifies the acceptable pH range and appearance of solutions. It replaces earlier standards ISO 419:1972 and ISO 3300:1976, consolidating test procedures for reliability and practical application in photographic chemical processing.
Key Topics
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Purity specifications:
- Anhydrous sodium thiosulfate assay ≥ 97% (mass/mass)
- Sodium thiosulfate pentahydrate assay between 99% and 101% (mass/mass)
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Impurities limits:
- Insoluble matter (max. 0.4% for anhydrous, 0.2% for pentahydrate)
- Heavy metals (max. 0.002% for anhydrous, 0.001% for pentahydrate)
- Iron content (max. 0.005% anhydrous, 0.003% pentahydrate)
- Alkalinity (as NaOH), max. 0.06%
- Acidity (as H2SO4), max. 0.01%
- Sulfide content (max. 0.0006% anhydrous, 0.0004% pentahydrate)
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pH requirements:
- Solutions must have a pH between 6.5 and 9.5 for optimal photographic use
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Appearance:
- Solutions should be clear and free from visible insoluble matter except slight flocculence
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Analytical methods:
- Chemical assays via titration and instrumental analysis based on referenced ISO 10349 parts (General, Insoluble matter, Heavy metals, Alkalinity/acidity, Sulfide determination)
- Emphasis on practical test methods suitable for standard laboratories without specialized equipment
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Safety guidelines:
- Handling procedures highlighting the use of protective apparel due to caustic or toxic chemicals involved in testing
- Hazard warnings aligned with ISO 10349-1 requirements
Applications
ISO 10636:1994 is essential in the photographic industry for quality assurance of sodium thiosulfate chemicals used in photographic film and paper processing. Ensuring chemical purity according to these specifications minimizes undesirable effects such as image degradation, inconsistent development, or contamination.
Typical applications include:
- Manufacturing and quality control of photographic chemical solutions
- Testing incoming chemical batches for purity verification
- Ensuring compliance for photographic processing labs and suppliers
- Supporting photographic engineers in optimizing processing chemistry performance
By adhering to ISO 10636, stakeholders achieve consistent photographic results, reduce waste, and maintain environmental and health safety standards during chemical handling.
Related Standards
ISO 10636 references several complementary ISO standards that specify methods for testing related chemical properties in photographic-grade materials:
Using these standards in conjunction provides a comprehensive framework for evaluating the chemical quality essential for photographic processing chemicals.
Keywords: ISO 10636, sodium thiosulfate specifications, photographic processing chemicals, chemical purity requirements, photographic-grade chemicals, photographic chemical testing, anhydrous sodium thiosulfate, sodium thiosulfate pentahydrate, ISO 10349, photographic materials quality standards, photography chemical analysis
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