Overview
EN ISO 19399:2017 (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 wedge-cut (scribe or drill) creates a controlled damage whose geometric projection is measured with a measuring microscope; film thickness is calculated from the measured base and the wedge-cut angle (t = l · tan α). The method is suitable for most coat–substrate combinations and can resolve single film thicknesses within multilayer coating systems.
Key topics and requirements
- Scope and applicability
- Destructive method for dry-film thickness measurement.
- Applicable to single coats and multilayer coating systems where microscopic contrast exists.
- CEN adoption of ISO 19399:2016 (EN ISO 19399:2017).
- Two methods
- Method A - wedge-cut scribe (linear scribe flank measured microscopically).
- Method B - wedge-cut bore/drill (conical bore; concentric circles measured).
- Measurement principle
- Film thickness calculated using the wedge-cut base (l) and wedge angle (α): t = l · tan α.
- Instruments may express readings in scale divisions or micrometres; wedge-cut factor (tan α) or divisor is used for conversion.
- Apparatus and microscope limits
- Measuring microscope with adequate depth of field and scale resolution.
- Wedge-cut tools with defined flank angles (examples given: 5.7° and 14.0°).
- Example measuring ranges: up to ~200 µm (α = 5.7°) and up to ~500 µm (α = 14.0°); example absolute resolutions 2 µm and 5 µm respectively.
- Limitations
- Not suitable or restricted for: very soft/elastic coatings or substrates, very hard (unscribable) substrates, poor visual contrast between coating and substrate, or film thicknesses exceeding microscope depth of field.
- Normative reference: ISO 4618 (terms and definitions).
Applications and users
- Practical applications:
- Quality control and verification of dry film thickness in paint and varnish production.
- Determination of single coat thicknesses in multilayer coating systems.
- Failure analysis and laboratory assessment where destructive measurement is acceptable.
- Typical users:
- Coatings test laboratories, R&D and QC teams in paint manufacturers, corrosion engineers, inspection bodies, and standards/specification writers.
Related standards
- ISO 4618 - Paints and varnishes: terms and definitions (normative reference used by EN ISO 19399:2017).
- EN ISO 19399:2017 is the CEN-endorsed European version of ISO 19399:2016.
Keywords: EN ISO 19399:2017, ISO 19399:2016, wedge-cut method, scribe and drill method, dry film thickness, paints and varnishes, coating systems, measuring microscope.