What is Gloss Measurement of the Paint / Coating , ASTM D523 & ISO 2813 Explained with Angles

What is Gloss of Paint / Coating: 

Gloss is the ability of a painted surface to reflect light in a mirror-like (specular) direction.

• Smooth surface → high gloss
• Rough / matte surface → low gloss

*Gloss is measured in Gloss Units (GU) using a Gloss meter.

Measurement Principle (How Gloss Meter Works):-

1. A light beam strikes the surface at a fixed angle

2. Light reflects from the surface

3. A detector measures reflected light intensity

4. Result is compared with a black glass standard

5. Value displayed in Gloss Units (GU)

*Calibration standard: Polished black glass = 94.8 GU at 60°

                                         

Why Three Angles Are Needed:-

One angle cannot accurately differentiate very shiny or very dull surfaces.

So both ASTM D523 and ISO 2813 define three geometries:

Angle	Purpose
20°	High-gloss surfaces
60°	Universal / reference angle
85°	Low-gloss / matte surfaces

Detailed Angle Explanation:-

20° Angle (High Gloss)

• Used for automotive top coat
• Powder clear coat
• Piano black finishes

Why 20°?

• At low angle, slight surface defects cause large changes in reading

Typical range:

70 – 100+ GU

 60° Angle (Standard Angle)

• Most commonly used
• Quality control reference angle

Used for:

• Liquid  paint
• Powder coating
• CED Base coat
• Appliance coating

Typical range:

10 – 70 GU

 85° Angle (Low Gloss / Matte)

• For textured & matte paints
• Low sheen powder coating

Why 85°?

• At high angle, matte surfaces reflect more measurable light

Typical range:

0 – 10 GU (measured at 60°)

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