🔩 Specular gloss of paint coatings — measurement with a glossmeter at 20°, 60° and 85°
In short
The glossmeter measures the light reflected specularly from the coating and relates it to a standard of polished black glass with a refractive index of 1. The test is performed according to PN-EN ISO 2813:2014-11; Measuring geometries: 20° — high-gloss surfaces; 60° — semi-gloss surfaces; 85° — matt surfaces. The procedure comprises 8 steps; it is used for: Quality control of paint coatings on industrial products and rolling stock, Acceptance of paint coatings on steel structures and rail vehicles, Assessment of gloss loss after natural and accelerated ageing.
At a glance
- Standard: PN-EN ISO 2813:2014-11
- Category: Materials and NDT
- Procedure steps: 8
- Measuring geometries: 20° — high-gloss surfaces; 60° — semi-gloss surfaces; 85° — matt surfaces
- Rule for selecting the geometry: By default 60°; 20° geometry for high-gloss surfaces, 85° for matt surfaces. The numerical thresholds used in practice (above 70 GU at 60° for the 20° geometry, below 10 GU at 60° for the 85° geometry) come from an industry publication, not from the text of the standard
- Unit: Gloss units GU; gloss must not be expressed as a percentage
Overview
The standard specifies a method for determining the gloss of coatings using three measuring geometries: 20°, 60° and 85°. The method is suitable for measuring the gloss of non-textured coatings. The gloss value is given in gloss units (GU); gloss values must not be interpreted or expressed as percentages. The gloss scale is defined by assigning a value of 100 gloss units to polished black glass with a refractive index of 1.567 for all three geometries.
Because gloss characteristics are non-linear, each measuring angle can differentiate gloss only within a certain range. The following angles have proved themselves in practice: the 20° geometry for high-gloss surfaces, the 60° geometry for semi-gloss surfaces and the 85° geometry for matt surfaces. The geometry used must be stated with each gloss value. In industrial practice the 60° geometry is used by default, and 20° and 85° in special cases: 20° for surfaces with a gloss above 70 GU at 60°, and 85° for surfaces below 10 GU at 60°.
Gloss measurement is one of the standard tests of paint coatings, alongside the measurement of thickness, hardness, colour, adhesion, and corrosion and weathering resistance. The result is a measure of the quality of workmanship of the coating and its aesthetic qualities, and in contractual assessments acceptance criteria are set, including the permissible loss of gloss after ageing.
Method principle
The principle of gloss measurement is based on measuring directionally reflected light. A glossmeter is used to determine the gloss values of coated surfaces, correlated with the visual impression of gloss: the ratio of the gloss of the coating to the gloss of a polished flat glass plate with a specified reference refractive index is measured. The standard is polished black glass with a refractive index of 1.567 at a wavelength of 587.6 nm, measured in the specular direction for the given angle of reflection, which is assigned a value of 100 gloss units for all three geometries. The result is given in gloss units (GU), always together with the measuring geometry.
Applications
- Quality control of paint coatings on industrial products and rolling stock
- Acceptance of paint coatings on steel structures and rail vehicles
- Assessment of gloss loss after natural and accelerated ageing
- Comparison of batches of coating materials and control of application repeatability
- Assessment of the effectiveness of local coating repairs
Key parameters
| Parameter | Value |
|---|---|
| Measuring geometries | 20° — high-gloss surfaces; 60° — semi-gloss surfaces; 85° — matt surfaces |
| Rule for selecting the geometry | By default 60°; 20° geometry for high-gloss surfaces, 85° for matt surfaces. The numerical thresholds used in practice (above 70 GU at 60° for the 20° geometry, below 10 GU at 60° for the 85° geometry) come from an industry publication, not from the text of the standard |
| Unit | Gloss units GU; gloss must not be expressed as a percentage |
| Standard | Polished flat black glass with a refractive index of 1.567 at 587.6 nm, with a value of 100 GU for all three geometries |
| Repeatability of readings | Differences between measurements should not exceed 5 GU; otherwise the number of readings is increased |
| Limitation | Method intended for non-textured coatings |
| Reporting the result | The geometry used is stated with each gloss value |
Standard
- Standard number
- PN-EN ISO 2813:2014-11
- Title (PL)
- Farby i lakiery — Oznaczanie połysku powłok niemetalicznych przy kącie 20°, 60° i 85°
- Title (EN)
- Paints and varnishes — Determination of gloss value at 20°, 60° and 85°
Step-by-step procedure
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Surface preparation
The coating to be measured is to be non-textured, uniform, clean and dry; remove dust, grease and dirt that alter the directional reflection.
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Conditioning
Condition the coated panels under specified conditions of temperature and humidity until the coating is completely dry and cured.
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Checking the glossmeter
Calibrate the instrument on the polished black glass standard with a refractive index of 1.567, which is assigned a value of 100 GU, and then check the readings on a working standard in the range of the expected values.
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Selection of the geometry
Make an orientation measurement at 60°. In industrial practice it is assumed that a result above 70 GU directs to the 20° geometry, and below 10 GU to the 85° geometry; these numerical thresholds come from an industry publication and not from the text of the standard, so check the requirement applicable to the specific product in the specification or in the standard itself. The standard only indicates that 20° is used for high-gloss surfaces, 60° for semi-gloss and 85° for matt surfaces.
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Measurement
Place the glossmeter head on the surface so that it rests over the whole measuring aperture, and read the value. Take several readings at different places on the surface.
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Assessment of scatter
Check the scatter of the readings: the differences between measurements should not exceed 5 GU. With greater scatter increase the number of readings.
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Result
Give the mean value in gloss units together with the geometry used, for example "68 GU at 60°"; do not convert the result to percentages.
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Report
In the report give the identification of the product and the substrate, the method of application and the drying conditions of the coating, the conditioning conditions, the instrument and standards used, the measuring geometry, the number of readings, the values and the mean result, and the acceptance criteria, if specified.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Glossmeter (reflectometer) | Instrument with 20°, 60° and 85° geometries, reading in gloss units | — |
| Polished black glass standard | Flat plate with a refractive index of 1.567, reference value 100 GU | — |
| Working standards | Plates with lower gloss values for checking the linearity of readings in the working range | — |
| Test panels | Standard panels according to ISO 1514 with a coating applied at uniform thickness | — |
| Coating thickness gauge | Magnetic or induction — coating thickness check accompanying the gloss assessment | — |
| Climatic chamber | Conditioning of the panels before measurement under specified conditions of temperature and humidity | — |
Health and safety (OHS)
- Solvents and coating materials during panel preparation — ventilation, gloves, no open flame
- Vapours of volatile organic compounds during coating drying — extraction above the workstation
- The black glass standard is fragile and easily scratched — store it in its case, clean with a soft cloth
- Work on freshly painted surfaces — wait for the full curing time before measuring
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN ISO 2813:2014-11 — “Paints and varnishes — Determination of gloss value at 20°, 60° and 85°”.
How does this method work?
The principle of gloss measurement is based on measuring directionally reflected light. A glossmeter is used to determine the gloss values of coated surfaces, correlated with the visual impression of gloss: the ratio of the gloss of the coating to the gloss of a polished flat glass plate with a specified reference refractive index is measured.
What is the measuring range and accuracy?
Measuring geometries: 20° — high-gloss surfaces; 60° — semi-gloss surfaces; 85° — matt surfaces; Rule for selecting the geometry: By default 60°; 20° geometry for high-gloss surfaces, 85° for matt surfaces. The numerical thresholds used in practice (above 70 GU at 60° for the 20° geometry, below 10 GU at 60° for the 85° geometry) come from an industry publication, not from the text of the standard; Unit: Gloss units GU; gloss must not be expressed as a percentage; Standard: Polished flat black glass with a refractive index of 1.567 at 587.6 nm, with a value of 100 GU for all three geometries.
How long does the test take?
The procedure comprises 8 steps. The standard does not give a duration for every stage — the laboratory's own procedure decides.
What equipment is required?
Glossmeter (reflectometer), Polished black glass standard, Working standards, Test panels, Coating thickness gauge, Climatic chamber.
Where is this test used?
Quality control of paint coatings on industrial products and rolling stock; Acceptance of paint coatings on steel structures and rail vehicles; Assessment of gloss loss after natural and accelerated ageing; Comparison of batches of coating materials and control of application repeatability; Assessment of the effectiveness of local coating repairs.
What safety precautions apply?
Solvents and coating materials during panel preparation — ventilation, gloves, no open flame; Vapours of volatile organic compounds during coating drying — extraction above the workstation; The black glass standard is fragile and easily scratched — store it in its case, clean with a soft cloth; Work on freshly painted surfaces — wait for the full curing time before measuring.
Which laboratory can perform this test?
The test is performed by laboratories accredited to ISO/IEC 17025. On LabCoda you can find them by the standard number PN-EN ISO 2813.