Overview
ISO 787-17:2019 - General methods of test for pigments and extenders - Part 17 - specifies a comparative laboratory method to determine the lightening (reducing) power of white pigments against an agreed reference sample of the same type. The standard defines two procedures:
- Procedure A: quicker, suited to testing a single sample;
- Procedure B: more exhaustive, suited to multiple samples or pigments of unknown lightening power.
The method uses a prepared blue paste into which measured amounts of the test and reference white pigments (e.g., titanium dioxide, zinc oxide, lithopone, zinc sulfide) are dispersed, followed by visual comparison of opaque strips on a glass slide under diffuse daylight.
Key topics and requirements
- Blue paste composition (example quantities provided): castor oil (500 g), precipitated calcium sulfate CaSO4·2H2O (475 g), ultramarine blue (5 g), treated natural earth (20 g).
- Sample preparation: dispersion of measured pigment masses into 5 g of blue paste using an automatic muller (ground-glass plates, up to ~1 000 N force, specified revolutions) or by hand muller/palette knife.
- Reference masses (Procedure A examples): zinc oxide/lithopone 0.500 g; high‑grade zinc sulfide 0.200 g; titanium dioxide 0.100 g. Procedure B uses a series of reference masses (see standard) to derive percentage lightening power.
- Comparison method: spread pastes in opaque strips on a glass slide and compare intensity in diffuse daylight (or artificial daylight if necessary).
- Expression of results: relative lightening power = 100 × (mass of reference pigment / mass of test pigment) (Procedure A) or read/ interpolate percentage from the Procedure B reference series.
- Reporting: identify pigment tested, reference to ISO 787-17:2019, test conditions and results.
Applications and users
ISO 787-17:2019 is practical for:
- Quality control laboratories in pigment manufacturing and paint/varnish production;
- R&D and formulation teams comparing titanium dioxide and alternative white pigments;
- Procurement and specification teams requiring standardized comparative data on lightening power;
- Conformity assessment and product specification writers who need repeatable, documented test results.
Keywords: ISO 787-17:2019, lightening power, white pigments, titanium dioxide, zinc oxide, lithopone, test method, pigment comparison.
Related standards
- ISO 788 - Ultramarine pigments for paints (referenced for ultramarine blue);
- ISO 15528 - Sampling of paints, varnishes and raw materials;
- ISO 18451-1 - Pigments, dyestuffs and extenders - Terminology (general terms);
- ISO 787 series - other general test methods for pigments and extenders.
