ISO 787-25:2019

Overview

ISO 787-25:2019 specifies a colorimetric test method for comparing the colour, in full‑shade (optically hiding) systems, of white, black and coloured pigments against an agreed reference pigment. The standard describes preparation of a defined test medium, dispersion and specimen preparation, colour measurement using spectrometers or tristimulus colorimeters, and expression of results (e.g., relative hue, lightness, chroma and total colour difference).

Keywords: ISO 787-25, pigments, extenders, colour comparison, colorimetric method, full-shade systems, pigment testing, spectrometer, tristimulus colorimeter.

Key topics and technical requirements

• Scope and principle
  • Compares the colour of a test pigment and an agreed reference in a single‑pigment (mass tone/full shade) system using tristimulus measurements and colourimetry (ISO 18314-1; ISO 11664-4 for derived attributes).
• Test medium
  • Preferred binder: an alkyd resin composed of 63% linseed oil, 23% phthalic anhydride, 14% trimethylol propane with specified acid value, viscosity and hydroxyl value.
  • Fumed silica (to prevent flocculation and control flow) blended at a recommended ratio; preferred mix: 97 parts alkyd : 3 parts fumed silica, dispersed on a triple‑roll mill.
  • Fumed silica requirements include BET surface area 175–225 m2/g and pH of a 4% aqueous dispersion 3.6–4.5.
• Sample preparation and apparatus
  • Use of an automatic muller (ground‑glass plates), triple‑roll mill for pre‑dispersion, film applicator, suitable non‑fluorescent substrates and stencils/glass covers.
• Measurement and instrument requirements
  • Spectrometer or tristimulus colorimeter per ISO 18314‑1.
  • Special provisions for black pigments: high instrument accuracy, zero adjustment using a light‑trap black standard and repeatability requirement where standard deviation σ of consecutive tristimulus measurements must be < 0.005 (20 measurements).
• Results reporting
  • Expression of relative hue/amount of relative hue (white/black pigments), lightness difference, and colour difference metrics for coloured pigments. Test report items are specified.

Applications and who uses it

• Pigment manufacturers for quality control and batch-to-batch colour matching.
• Paints, coatings and ink formulators to verify pigment behaviour in full‑shade systems.
• Testing laboratories and QC departments that conduct standardized colour comparisons.
• Procurement and compliance teams requiring reproducible, comparable colour data for supplier agreements.

Related standards

• ISO 18314‑1/2 (analytical colourimetry), ISO 11664‑4 (colour attributes), ISO 787 series parts (e.g., ISO 787‑9, ISO 787‑24), ISO 8780‑6 and others referenced for sampling, dispersion and instrument methods.

This concise, technical method ensures reproducible, comparable colour assessment of pigments in full‑shade systems, supporting quality control and specification compliance across coatings and colourant industries.