Overview
ISO 4620:1986 - "Cadmium pigments - Specifications and methods of test" defines quality requirements and laboratory test methods for inorganic cadmium pigments used in paints, plastics, rubber and ceramics. The standard covers pigments made predominantly of cadmium sulfide or mixed crystals of cadmium sulfide and cadmium selenide, with possible partial substitution of cadmium by zinc. It classifies pigments into three types (concentrated, extended and essentially pure) and specifies chemical, physical and purity criteria plus agreed test procedures.
Key topics and technical requirements
- Pigment types
- Type 1: concentrated (≤ 30% extenders) - general-purpose.
- Type 2: extended (≤ 70% extenders) - processing/Cost-adjusted.
- Type 3: unextended (essentially pure) - mainly for ceramics.
- Minimum active content (sum of Cd + Zn + Se + S) required by type (e.g., high minimum for type 3).
- Physical and chemical limits
- Matter volatile at 105 °C, matter soluble in water, residue on 45 µm sieve and pH range (5–8).
- Limits for soluble fraction in dilute HCl (national limits may override).
- Impurity limits (examples specified): antimony, arsenic, barium, chromium, lead and mercury are restricted to low ppm/% levels to control toxicity and regulatory compliance.
- Analytical methods
- Wet-chemical and instrumental procedures are described: dissolution, masking (potassium cyanide), complexometric titration with EDTA (for Cd + Zn), back-titration (magnesium sulfate), selenium gravimetric determination (bromine oxidation and hydrazinium reduction), and sulfur determination.
- References to instrumental standards (atomic absorption, XRF) and laboratory practice (glassware and water quality) are included.
Applications and who uses ISO 4620
- Pigment manufacturers - to specify product quality, classify grades, and ensure compliance with market/regulatory limits.
- Quality control laboratories - to perform reproducible tests for composition, impurities and performance-related properties.
- Paint, plastic and ceramic formulators - to select appropriate pigment type (concentrated vs extended vs pure) for colour strength, heat stability and processing.
- Procurement and regulatory bodies - to verify material conformity and safety-related metal limits.
Related standards
ISO 4620 references several complementary standards for test techniques and laboratory practice, for example:
Keywords: ISO 4620, cadmium pigments, cadmium sulfide, cadmium selenide, pigment specifications, methods of test, EDTA titration, selenium determination, pigment quality.