Overview
EN ISO 2495:2000 (ISO 2495:1995) specifies the composition, physical characteristics and test methods for iron blue pigments (commonly known as Prussian blue and related ferrocyanide/ ferricyanide iron pigments). It replaces the first edition (1972) and provides laboratory procedures and acceptance criteria used in pigment quality control and specification for the paint, coating and printing industries.
Key topics and requirements
- Definition: An iron blue pigment is formed by reaction of iron salts with cyanoferrate(II) or cyanoferrate(III) ions (with optional oxidation steps).
- Composition requirements:
- The sum of iron(II) + iron(III) ions together with the iron-cyanoferrate complex (expressed as Fe(CN)6) shall meet a minimum content specified in the standard.
- Total iron content has a specified minimum (see standard text).
- Physical appearance: Material must be a soft dry powder or be readily reduced to that form without grinding (palette-knife crushable).
- Chemical and physical limits (examples from the standard):
- Volatile matter: specified range (see clause/table).
- Matter soluble in water: maximum permitted value (hot extraction method).
- Acidity/alkalinity of aqueous extract: maximum titratable acidity per 100 g pigment.
- Identification test: Alkali treatment should destroy the blue coloration and reformation of the characteristic iron blue on acidification - used to detect added non-iron colouring matter.
- Analytical test methods:
- Two procedures for determining basic iron and hexacyanoferrate content are provided. Method A is the referee method and uses KOH decomposition with titrations (dichromate, permanganate/thiosulfate) and associated reagents/indicators. Method B is an alternative involving NaOH decomposition and permanganate titration.
- Conditional requirements (by agreement): colour match to a reference pigment, relative tinting strength, ease of dispersion, oil absorption tolerance (e.g., ±10% from agreed value).
Applications and users
- Quality control laboratories in pigment manufacturing and distribution
- Paint, varnish and ink manufacturers specifying Prussian/iron-blue pigments
- Procurement/specification teams requiring compliance checks for pigment shipments
- Regulatory and standards compliance officers verifying product conformity
- R&D teams evaluating pigment dispersion, tinting strength and compatibility
Related standards
Standards referenced by EN ISO 2495 (used for sampling and specific test procedures) include:
- ISO 787 series (general pigment test methods: volatile matter, water‑soluble matter, oil absorption, tinting strength)
- ISO 842 (sampling of raw materials for paints and varnishes)
- ISO 3696 (water for analytical use)
- ISO 385-1, ISO 648, ISO 1042 (laboratory glassware)
- ISO 8780-2 (dispersion methods)
For detailed numeric limits, stepwise procedures, precision statements and safety precautions (use of analytical-grade reagents, mercury handling note, waste treatment), consult the full EN ISO 2495:2000 / ISO 2495:1995 text.
