ISO 787-8:2000

Overview

ISO 787-8:2000 defines a standardized laboratory method - the cold extraction method - for determining the percentage by mass of matter soluble in water in pigments and extenders. It is one part of the ISO 787 series of general test methods for pigments and extenders and is intended for use in quality control, materials specification and product testing within the paint, coatings and pigment industries.

Key topics and requirements

• Scope: Determines water‑soluble matter in a pigment or extender sample using cold extraction (room temperature).
• Sample mass: Typical test portions are 2 g to 20 g; choose mass according to expected soluble content and use the same mass for repeats.
• Reagents & apparatus: Fresh double‑distilled or de‑ionized water (pH 6–7), one‑mark 250 ml volumetric flask, membrane filter (or centrifuge), evaporating dish, water bath, oven at (105 ± 2) °C, balance accurate to 1 mg.
• Procedure (summary):
  • Moisten test portion; add wetting agent or ethanol where necessary (example: 10 ml of 0.01% ethylene oxide condensate for pigments soluble in ethanol).
  • Add 200 ml water at room temperature, stir continuously for 1 hour.
  • Transfer to a 250 ml volumetric flask, dilute to mark, mix, and filter (or centrifuge) until clear.
  • Pipette 100 ml of filtrate, evaporate, dry at 105 °C, and weigh the residue to 1 mg precision.
• Calculation: Convert the residue mass to mass percent of the original test portion. The standard gives the calculation:
  • M_ws,c (%) = (m1 × 2.5 / m0) × 100
    • where m1 = mass of residue from 100 ml filtrate, m0 = mass of test portion.
• Repeatability & reporting rules: Perform duplicate determinations; if results differ by >10% of the lower value, perform a third test and report the arithmetic mean. Express results to one decimal place.
• Factors affecting reproducibility: Type of water, type of filter, and test portion mass.

Applications and users

• Quality control laboratories in paints, coatings and pigment manufacturing
• Raw material suppliers and spec writers who must state water‑soluble content in datasheets
• R&D and analytical labs comparing cold versus hot extraction (see related Part 3)
• Compliance testing where the specification explicitly requires the cold extraction method

Related standards

• ISO 787-3: Hot extraction method for matter soluble in water (comparison with cold extraction)
• ISO 1042: Laboratory glassware - One‑mark volumetric flasks
• ISO 15528: Sampling of paints, varnishes and raw materials

Keywords: ISO 787-8:2000, cold extraction, matter soluble in water, pigments, extenders, water‑soluble matter test, paint industry, quality control.