Overview
ISO 19399:2016 - Paints and varnishes - Wedge-cut method for determination of film thickness (scribe and drill method) - specifies a destructive microscopic method to determine dry film thickness of coatings. The standard covers both single coats and multi‑coat systems by mechanically creating a controlled wedge cut (either by scribing or drilling) and measuring the projection of the wedge flank with a measuring microscope. It is suitable for almost all coat–substrate combinations, with specific limitations noted for very soft/elastic coatings, very hard substrates, low visual contrast, or very thick films exceeding the microscope depth of field.
Key topics and technical requirements
- Principle: create a wedge cut with known flank angle α and calculate dry-film thickness t from the measured wedge‑cut base l using t = l · tan α.
- Two methods:
- Method A (wedge‑cut scribe) - linear scribing stylus.
- Method B (wedge‑cut bore/drill) - conical drill bit creating concentric circles.
- Apparatus:
- Wedge‑cut stylus or drill bit with specified wedge‑cut angle/factor.
- Measuring microscope: minimum 40× magnification, measuring range ≥ 2 mm, scale division ≤ 0.02 mm. Video microscopes may be used.
- Measurement procedure:
- Apply three wedge cuts per determination; measure each cut at two points.
- Optionally apply a thin contrast mark (black or white felt‑tip) to aid microscopy.
- Performance examples:
- Typical wedge angles: 5.7° (tan α ≈ 0.10) and 14.0° (tan α ≈ 0.25).
- With a 2 mm microscope range, film thickness measuring ranges approx. up to 200 µm (5.7°) or up to 500 µm (14.0°); resolution examples given in the standard.
- Limitations: unsuitable or restricted for very soft/elastic coatings (no clear scribe), very hard coatings/substrates (cannot be scribed/drilled), low coating–substrate contrast, or film thickness beyond microscope depth of field.
Applications and who uses it
- Quality control and acceptance testing in coatings manufacturing and application
- Laboratory measurement of dry film thickness for single coats and multi‑layer coating systems
- Failure analysis, R&D, surface engineering and materials testing where precise layer thicknesses are required
- Typical users: paint and varnish manufacturers, independent testing labs, coating inspectors, automotive and industrial maintenance teams, research institutions
Related standards
- ISO 4618 - Paints and varnishes: terms and definitions (referenced)
- ISO 2808 - Definitions related to dry‑film thickness (referenced)
- ISO 19399:2016 is prepared by ISO/TC 35 (Paints and varnishes), SC 9 (General test methods)
Keywords: ISO 19399:2016, wedge‑cut method, dry film thickness, scribe and drill method, paints and varnishes, measuring microscope, wedge‑cut stylus, wedge‑cut drill, destructive film thickness measurement.