Overview
ISO 3619:1994 - "Photography - Processing chemicals - Specifications for ammonium thiosulfate solution" defines purity criteria and test methods for photographic‑grade ammonium thiosulfate solution. This second edition (1994) cancels ISO 3619:1976 and establishes mandatory limits and analytical procedures to ensure chemicals used in photographic processing do not produce undesirable photographic effects.
Key topics and technical requirements
The standard specifies chemical and physical limits, mandatory tests, and referenced methods (many from ISO 10349 series). Major requirements include:
- Assay (as ammonium thiosulfate (NH4)2S2O3): 53.0% (m/m) minimum and 61.0% (m/m) maximum
- Alkalinity (as NH4OH): 0.3% (m/m) minimum and 1.5% (m/m) maximum
- Sulfite content (as (NH4)2SO3): maximum 1.0% (m/m)
- Insoluble matter: maximum 0.2% (m/m) - determined as precipitate after treatment in ammonium hydroxide (ISO 10349‑3)
- Residue after ignition: maximum 0.2% (m/m) (ISO 10349‑4)
- Heavy metals (as Pb): maximum 0.001% (m/m) (ISO 10349‑5)
- Iron (Fe): maximum 0.001% (m/m) (ISO 10349‑5)
- Sulfide (as S2‑): maximum 0.00025% (m/m) (ISO 10349‑10)
- Specific gravity / density at 20 °C: specific gravity 1.290–1.346 or density 1.284–1.340 g/ml (ISO 10349‑11 / ISO 10349‑12)
The standard prescribes titrimetric and gravimetric methods for assay and impurity testing, and requires tests be performed on samples “as received.” It also includes handling/storage guidance (store in closed container at room temperature; avoid mixing with strong acids/alkalis).
Applications and users
ISO 3619 is intended for:
- Chemical manufacturers and suppliers producing photographic‑grade ammonium thiosulfate solution
- Quality control and analytical laboratories performing purity testing and batch release
- Photographic processors and labs that require assurance of chemical quality to avoid processing defects
- Procurement specialists and standards officers specifying compliance requirements in supply contracts
Use of ISO 3619 helps reduce image defects, ensures consistent processing performance, and facilitates vendor qualification and regulatory compliance.
Related standards
ISO 3619 references and relies on test methods in the ISO 10349 series (Parts 1, 3, 4, 5, 10, 11, 12) for general procedures, insoluble matter, residue after ignition, heavy metals/iron, sulfide, and specific gravity/density determinations.
Keywords: ISO 3619:1994, ammonium thiosulfate solution, photographic‑grade, processing chemicals, purity criteria, assay, specific gravity, ISO 10349, quality control.