Overview
EN 20105-A02:1994 (identical to ISO 105‑A02:1993) specifies the grey scale for assessing change in colour in textile colour‑fastness tests. Published by CEN/ISO, the standard defines a permanent, colorimetric reference scale - including an essential 5‑step scale and an augmented 9‑step (g‑step) version - against which tested samples and working standards are visually compared to assess perceived colour change.
Key topics and technical requirements
- Scale format
- Essential 5‑step grey scale: five pairs of non‑glossy grey chips or swatches illustrating contrast levels corresponding to ratings 5, 4, 3, 2, 1.
- Augmented (g‑step) scale: adds four half‑steps (4‑5, 3‑4, 2‑3, 1‑2) for a 9‑step assessment.
- Colorimetric specification
- The scale is precisely specified by colorimetric data so it can serve as a permanent reference for preparing and checking working standards.
- Chips/swatches shall be measured with a spectrophotometer including the specular component; tristimulus Y value for the first (neutral) member is 12 ± 1 (as given in the standard).
- Colorimetric calculations use the CIE supplementary standard colorimetric system (10° observer) for the appropriate D‑series illuminant as specified in the document.
- Visual assessment procedure
- Place original and tested specimen side‑by‑side on the same plane with the grey scale nearby; surround with a neutral grey field.
- Recommended illumination: equivalent natural sky light or an artificial source of ≥ 600 lx; sample illuminated at about 45°, viewing approximately perpendicular.
- Where backing effects occur, use multiple layers of the textile under both specimens.
- Rating is the grey‑scale step whose perceived difference most closely matches the difference between original and tested specimens; intermediate contrasts are recorded as half‑steps.
- Reporting
- Numerical rating (1–5 or g‑step) and optional qualitative abbreviations (e.g., B = Bluer, R = Redder, W = Weaker) may be recorded to describe direction or character of change.
Applications and users
- Quality control and production testing in textile manufacturing, dyeing and finishing.
- Independent testing laboratories performing standard colour‑fastness assessments.
- Product specification and acceptance criteria for apparel, home textiles, upholstery, and technical textiles.
- Useful for R&D, supplier quality audits, and regulatory/compliance documentation where visual colour change must be quantified.
Related standards
- Part of the ISO 105 / EN 20105 series of colour‑fastness test methods. Users should consult other ISO/EN 105 parts for specific fastness tests (washing, light, rubbing, perspiration) that reference the grey‑scale assessment.