Overview - ISO 6504-1:2019 (Kubelka‑Munk method for white and light‑coloured paints)
ISO 6504-1:2019 specifies a standardized laboratory method to determine the hiding power (the spreading rate required to give 98% hiding) of white and light‑coloured paints using the Kubelka‑Munk (K‑M) optical model. The procedure applies to paint films with a CIE tristimulus value Y ≥ 70 and hiding power > 80%. It is not applicable to fluorescent or metallic paints. The method converts measured reflectance values into scattering and absorption coefficients and derives the wet film thickness that corresponds to 98% opacity (hiding).
Key technical topics and requirements
- Principle: Uses the Kubelka‑Munk equations to relate film reflectance to scattering (S) and absorption (a, b) coefficients and to predict hiding at a target reflectance ratio (Rfilm on black / R∞ ≈ 0.98).
- Measurements required:
- Reflectance of paint film on a black substrate (R_B).
- Reflectivity (R∞) - reflectance of an effectively infinitely thick film, typically measured on a white substrate.
- CIE tristimulus Y values (Y/100 used as reflectance input).
- Apparatus and materials:
- Substrates: polished black glass or polyester film and white/grey charts (ceramic or glass alternative).
- Film applicators (bar or wire‑wound) producing uniform wet films (typical 40–150 µm).
- Photoelectric reflectometer with spectral response approximating D65 × y(λ), accuracy ~0.1% full scale; 8°/diffuse geometry recommended in disputes.
- Templates and controlled application procedure.
- Calculations and output:
- Compute K‑M parameters (a, b) and St product from measured reflectances.
- Derive scattering coefficient S (S = St / t) and calculate hiding power V (V = 1000 / t for the film thickness t that yields 98% hiding).
- Limitations & precision: Not suitable for fluorescent or metallic paints; standard includes repeatability and reproducibility guidance and example graphs/tables (Annexes A–C) to simplify computation.
Practical applications and who uses this standard
- Quality control and batch release testing in paint and coatings manufacturing
- R&D and formulation optimization to compare pigment loading and extender efficiency
- Third‑party testing laboratories and certification bodies verifying opacity claims
- Specifiers, architects and procurement teams assessing coating performance
- Suppliers evaluating pigment/binder tradeoffs for cost vs. hiding efficiency
Benefits include objective, reproducible hiding‑power values, reduced extrapolation compared with full spreading‑rate tests, and direct linkage to optical parameters used in color/appearance engineering.
Related standards
Normative and complementary references used in ISO 6504-1:2019:
Keywords: ISO 6504-1:2019, hiding power, Kubelka‑Munk, paints and varnishes, reflectance measurement, scattering coefficient, paint opacity, white paints, light‑coloured paints.
Open preview (PDF)Paints and varnishes — Determination of hiding power — Part 1: Kubelka-Munk method for white and light-coloured paints