Overview
ISO 3621:1994 - Photography - Processing chemicals - Specifications for sodium tetraborate decahydrate - defines purity criteria and test methods for photographic‑grade sodium tetraborate decahydrate (Na2B4O7·10H2O). This second edition (1994) cancels and replaces the 1976 edition and is part of a series of ISO standards that set minimum quality and analytical requirements for photographic chemicals used in film and paper processing.
Key topics and requirements
- Scope and intent: Establishes chemical and physical requirements that correlate with undesirable photographic effects; tests are performed on samples “as received.”
- Physical form & storage:
- White crystalline powder or granules; relative molecular mass 381.37.
- Store in a closed container at room temperature.
- Mandatory purity limits (summary from Table 1):
- Assay (Na2B4O7·10H2O): ≥ 99.0% (m/m)
- Heavy metals (as Pb): ≤ 0.002% (m/m)
- Iron (Fe): ≤ 0.003% (m/m)
- pH (20 °C): 9.14 – 9.34
- Reaction to ammoniacal silver nitrate: To pass test
- Appearance of 20 g/L solution: Clear and free from insoluble matter except for slight flocculence
- Analytical methods:
- Assay based on a 20 g/L test solution and titration procedures (mannitol reaction and NaOH titration) using standardized reagents and apparatus.
- Heavy metals and iron determinations follow ISO 10349‑5 procedures.
- Reaction to ammoniacal silver nitrate follows ISO 10349‑9.
- pH measurement requires a calibrated electronic pH‑meter at 20 °C.
- Safety and laboratory practice: Uses potentially caustic/toxic reagents; follow ISO 10349‑1 guidance and standard laboratory safety (glasses, gloves, ventilation).
Applications and users
ISO 3621:1994 is intended for:
- Photographic chemical manufacturers and suppliers for product specification and quality control.
- Analytical and quality assurance laboratories performing acceptance testing of photographic-grade chemicals.
- Photographic processors and film/paper manufacturers seeking materials that will not impair photographic processing or image quality.
- Regulators and procurement teams specifying minimum purity for processing chemicals.
Practical benefits include ensuring consistent processing performance, minimizing image defects caused by impurities, and simplifying supplier acceptance testing.
Related standards
Keywords: ISO 3621, sodium tetraborate decahydrate, photographic chemicals, purity specification, assay, heavy metals, pH, ISO 10349.
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