Overview
ISO 8781-3:1990 defines a laboratory method for assessing the dispersibility of pigments and extenders by monitoring the change in specular gloss during progressive dispersion. The procedure compares a test pigment with an agreed reference: the pigment is dispersed in stages in a selected binder (agreed binder system), samples of the mill base are taken after each stage, films are prepared on a substrate, dried or stoved, and the specular gloss of each film is measured (per ISO 2813). Gloss values are plotted against dispersion stage (time, revolutions or passes) and the dispersion work required to reach a target gloss is determined by interpolation.
Key topics and requirements
- Purpose: comparative evaluation of dispersibility of pigments and extenders by tracking gloss development.
- Dispersion methods: use one of the methods described in the ISO 8780 series (machine dispersers, turbines, bead mills, three-roll mills, etc.). Read ISO 8780-1 in conjunction.
- Sample preparation: disperse pigment at agreed concentration in the chosen binder; take aliquots after each dispersion stage to make coating films.
- Film application and drying: apply films to agreed substrates (glass, panel, board) with uniform applicator; dry or stove under agreed conditions; maintain orientation consistency.
- Gloss measurement: measure specular gloss in triplicate using a glossmeter compliant with ISO 2813 (measurement angles such as 20°, 60°, 85° are referenced in ISO 2813).
- Data analysis: plot mean gloss vs dispersion stage (or inverse values); determine dispersion work needed to reach the agreed specular gloss value; report achieved maximum gloss if target not reached.
- Reporting: include product ID, references to ISO 8781-3 and relevant ISO 8780 part, binder type and pigment ratio, substrate and application method, target gloss, dispersion work (time, revolutions), graphical data, deviations and test dates.
- Annex A: mandatory supplementary information (dispersion method, binder designation and pigment/binder ratio, substrate and application, target gloss).
Practical applications and users
- Quality control labs and pigment manufacturers: establish batch-to-batch consistency and acceptance criteria for dispersibility.
- R&D and formulation teams (paints, coatings, inks): compare new pigments to reference standards and optimize milling/dispersing processes to reach required gloss levels.
- Suppliers and testing laboratories: provide objective, reproducible comparison of test pigment performance in a given binder system.
- Practical uses: optimize milling time, select dispersants or binders, evaluate processing stability (re-agglomeration or flocculation effects), and support specifications for paint and coating manufacture.
Related standards
- ISO 8781 (Parts 1–3) - general series on pigments and extenders dispersibility assessment.
- ISO 8780 series - methods of dispersion (machine, turbine, bead mill, three-roll mill, etc.).
- ISO 2813 - Determination of specular gloss of non-metallic paint films (referenced for gloss measurement).
Keywords: ISO 8781-3:1990, pigments, extenders, dispersibility, specular gloss, dispersion assessment, binder, mill base, ISO 2813, pigment testing, gloss measurement.
Open preview (PDF)Pigments and extenders — Methods of assessment of dispersion characteristics — Part 3: Assessment from the change in gloss