Overview
EN ISO 787-23:1995 (ISO 787-23:1979) is a general test method for determining the density of pigments and extenders by removing entrained air with a centrifuge. The method uses a displacement liquid of known density to wet a dried sample, centrifuges the mixture to expel occluded air, and calculates the sample density from mass differences. This standard is intended for use where the centrifuge method is appropriate and complements the pyknometer-based method given in Part 10 of ISO 787.
Key topics and requirements
- Principle: Wet a dried, sieved sample in a displacement liquid, centrifuge to remove entrained air, weigh the assembly in air and in the liquid, and calculate density from mass differences and the known density of the displacement liquid.
- Displacement liquid selection: Must be immiscible with the sample, have good wetting properties and low evaporation under vacuum. Recommended: high‑boiling aromatic or aliphatic hydrocarbons (boiling point > 170 °C).
- Temperature control: All weighings must be made at a constant temperature because liquid density is temperature‑dependent. Use a constant‑temperature room or enclosure where possible; if not, record temperature and apply corrections.
- Sample preparation:
- Mix and take representative sample per ISO 842.
- Sieve (nominal 500 µm) and dry at 105 ± 2 °C for 2 hours; cool in a desiccator.
- Typical sample mass: 1–10 g depending on expected density.
- Apparatus:
- Centrifuge tube (glass, polypropylene or stainless steel)
- Laboratory centrifuge (example: 4 500 r/min)
- Cradle and fine wire loop to suspend tube on balance
- Glass stirring rod, balance accurate to 1 mg
- Procedure highlights:
- Weigh empty tube assembly in air and suspended in displacement liquid.
- Add sample and liquid, stir, centrifuge (for 4 500 r/min ~ 15 min suggested) until occluded air is expelled and solids are closely packed.
- Refill tube to level, equilibrate to test temperature, weigh and compute density.
- Precision: Repeatability ~0.03 g/ml; reproducibility ~0.05 g/ml (95% probability).
Applications and users
- Quality control and R&D in paint, coatings and pigment manufacturing
- Materials testing laboratories measuring true density of pigments and extenders
- Specification writers and procurement teams requiring standardized density data for formulation and product comparison
- Useful where entrained air would bias density measured by other methods (e.g., bulk or tamped density measurements)
Related standards
- ISO 787-10 / EN ISO 787-10 - Density by pyknometer (alternative density method)
- ISO 842 - Sampling of raw materials for paints and varnishes
- Other parts of the ISO 787 series covering general test methods for pigments and extenders
Keywords: EN ISO 787-23, ISO 787-23, density determination, pigments and extenders, centrifuge method, displacement liquid, entrained air, paint testing, pyknometer alternative.