Overview
EN ISO 787-25:2019 - "General methods of test for pigments and extenders - Part 25: Comparison of the colour, in full-shade systems, of white, black and coloured pigments - Colorimetric method" - specifies a standardized, reproducible colorimetric procedure to compare the colour of a test pigment with an agreed reference pigment in full‑shade (hiding) systems. The method uses dispersed pigment specimens prepared in a defined test medium (an alkyd resin and fumed silica mix) and measures tristimulus values for quantitative colour comparison.
Key topics and technical requirements
- Scope and principle: Comparison of white, black or coloured pigments in full‑shade systems using a colorimetric procedure; measurement of tristimulus values and calculation of colour characteristics.
- Test medium and materials: Uses an alkyd resin binder blended with fumed silica as the specified medium for dispersion.
- Dispersion and apparatus: Pigments are dispersed using an automatic muller (or equivalent dispersion equipment); specific apparatus and sample substrates are defined to ensure repeatability.
- Specimen preparation: Procedures for preparing test portions and test specimens for white, black and coloured pigments (mass tone/full shade distinctions are covered).
- Measurements and calculations:
- Tristimulus measurements as described in ISO 18314-1 (analytical colorimetry).
- For white/black pigments: relative hue and amount of relative hue, plus lightness difference.
- For coloured pigments: lightness, hue, chroma and total colour difference using methods aligned with ISO colourimetry practice (ISO 11664-4 referenced).
- Sampling, expression of results and reporting: Includes requirements for sampling, reporting test conditions and expressing results numerically for quality control and specification.
Practical applications
- Quality control and batch acceptance testing for pigment manufacturers and extenders.
- Comparative colour specification when substituting pigments in paints, coatings and inks.
- R&D and formulation work where objective full‑shade colour matching is required (mass tone vs full shade assessment).
- Regulatory or procurement specifications that require standardized, reproducible colour comparison data.
Who should use this standard
- Pigment and extender manufacturers
- Paint, coatings and ink formulators
- Laboratory technicians in QC/QA roles
- Standards bodies and procurement specialists specifying pigment performance
Related standards
Keywords: EN ISO 787-25:2019, colorimetric method, pigments and extenders, full-shade systems, colour comparison, pigment testing, paint quality control.