ISO 788:2021

Overview

ISO 788:2021 - Ultramarine pigments - specifies requirements and corresponding test methods for artificial ultramarine pigments used in paints, plastics, rubbers and related applications. The second edition updates test procedures and tightens limits for impurities and elemental contaminants to support product quality, safety and regulatory compliance.

Key topics and technical requirements

• Scope and classification
  • Applies to artificial ultramarine pigments for coatings, plastics, rubbers, etc.
  • Two types by free sulfur content: Type A ≤ 0.05% and Type B ≤ 0.20% (mass fraction).
• Mandatory (basic) requirements
  • Matter soluble in water (hot extraction): Type A max 1.0%, Type B max 1.5% (ISO 787-3).
  • Residue on 63 µm sieve (water method): Type A max 0.1%, Type B max 0.5% (ISO 787-7).
  • Free sulfur determined by iodometric method (detailed procedure in Clause 7).
  • Matter volatile at 105 °C: max 1.0% (ISO 787-2).
  • Density at 23 °C: 2.23 to 2.40 g/cm3 (ISO 787-10).
  • Organic colouring matter: negative test (see ISO 1248:2006).
• Conditional requirements (to be agreed between parties)
  • pH, colour, relative tinting strength, oil absorption, resistance to light and resistance to bleeding (ISO 787 series and EN 14469-4 as applicable).
• Limitations on elemental contaminants (Clause 8)
  • Hg ≤ 1 mg/kg; Cd ≤ 5 mg/kg; Se ≤ 10 mg/kg; As ≤ 10 mg/kg; Cr, Pb, Sb ≤ 50 mg/kg; Ba ≤ 200 mg/kg.
• Sampling, marking and reporting
  • Sampling per ISO 15528; requirements for labelling and test reports are specified.

Practical applications and users

• Who uses ISO 788:2021:
  • Pigment manufacturers for product specification and QC.
  • Paint, coatings and plastics formulators to ensure compatibility and performance.
  • Quality control laboratories performing standardized tests (iodometric titration, sieve residue, water extraction, elemental analysis).
  • Procurement, compliance and regulatory teams verifying materials meet safety and elemental limits.
• Practical benefits:
  • Ensures consistent colour performance, particle quality and contaminant control.
  • Helps demonstrate conformity to international test methods and supports trade and regulatory acceptance.
  • Reduces risk of bleeding, lightfastness issues and hazardous elemental contamination in final products.

Related standards

• ISO 787 series (general test methods for pigments and extenders)
• ISO 3696 (water for analytical use), ISO 385, ISO 1042 (laboratory glassware)
• ISO 15528 (sampling), EN 14469-4 (bleeding in PVC)

Keywords: ISO 788:2021, ultramarine pigments, free sulfur, iodometric method, pigment test methods, pigments for paints plastics rubbers, elemental limits, ISO 787.