Appearance Measurement FAQs

Why measure gloss?

Gloss is an aspect of the visual perception of objects that is as important as colour when considering the psychological impact of products on a consumer.

It has been defined as ‘The attribute of surfaces that causes them to have shiny or lustrous, metallic appearance.’

The gloss of a surface can be greatly influenced by a number of factors, for example the smoothness achieved during polishing, the amount and type of coating applied or the quality of the substrate.

Manufacturers design their products to have maximum appeal- highly reflective car body panels, gloss magazine covers or satin black designer furniture.

It is important therefore that gloss levels are achieved consistently on every product or across different batches of products.

Gloss can also be a measure of quality of a surface, for instance a drop in the gloss of a coated surface may indicate problems with its cure- leading to other failures such as poor adhesion or lack of protection for the coated surface.

It is for these reasons that many manufacturing industries monitor the gloss of their products, from cars, printing and furniture to food, pharmaceuticals and consumer electronics.

What is a glossmeter?

A glossmeter (also known as a gloss meter) is an instrument that is used to measure the specular reflection of a surface such as gloss. Gloss is determined by projecting a beam of light at a fixed intensity and angle onto a surface and measuring the amount of reflected light at an equal but opposite angle.

What glossmeter do I need?

Identify the surface that you wish to measure. Is it a flat surface? If so, it can be measured with a traditonal glossmeter.

Curved surfaces should be measured using equipment specifically designed for this type of application. Benchtop and handheld instruments are available for these applications.

Selecting the correct glossmeter is dependent on the application and level of gloss of the surface. Each gloss meter specifies the measuring angles utilised.

‘Measurement angle’ refers to the angle between the incident and reflected light. Three measurement angles (20°, 60°, and 85°) are specified to cover the majority of coatings applications. The angle is selected based on the anticipated gloss range, as shown in the following table.

Gloss Range	60° Value	Notes
High Gloss	>70 GU	If measurement exceeds 70 GU at 60°, change test setup to 20°
Medium Gloss	10 – 70 GU
Low Gloss	<10 GU	If measurement is less than 10 GU, change test setup to 85°

Examples of high gloss finishes include:

Examples of medium gloss finishes include:

Examples of low gloss finishes include:

Selecting the correct angle for the application will optimise measurement accuracy.

Three types of instruments are available on the market: 60° single angle instruments, a combination of 20° and 60° and one type that combines 20°, 60° and 85°.

Two additional angles are used for other materials. An angle of 45° is specified for the measurement of ceramics, films, textiles and anodised aluminium, whilst 75° is specified for paper.

If a the appearance of a high gloss surface is affected by surface texture such as orange peel or a ‘milky’ finish or halos around reflections of bright light, these will need to be measured with the Rhopoint IQ

Novo Gloss Trigloss Glossmeter with Haze

• 20/60/85° Gloss meter for matt to mirror finishes
• Now features haze measurement to ASTM E430
• Full statistical analysis with trend graphs

Novo Gloss Trio Glossmeter

• 20/60/85° low cost glossmeter for all gloss applications
• Rapid data transfer
• Pass / Fail for easy identification of non conformances

Novo Gloss 60° Glossmeter

• 60 degree glossmeter for all gloss applications
• Easy reporting
• Pass / Fail for easy identification of non conformances

How is gloss measured?

A glossmeter (also gloss meter) is an instrument which is used to measure the specular reflection (gloss) of a surface. Gloss is determined by projecting a beam of light at a fixed intensity and angle onto a surface and measuring the amount of
reflected light at an equal but opposite angle.

There are a number of different geometries available for gloss measurement each being dependant on the type of surface to be measured. For non-metals such as coatings and plastics the amount of reflected light increases with an increase in the
angle of illumination as some of the light penetrates the surface material and is absorbed into it or diffusely scattered from it depending on its colour. Metals have a much higher reflection and are therefore less angularly dependant.

Many international technical standards are available that define the method of use and specifications for different types of glossmeter used on various types of materials including paint, ceramics, paper, metals and plastics. Many industries use glossmeters in their quality control to measure the gloss of products to ensure consistency in their manufacturing processes. The automotive industry is a major user of the glossmeter with applications extending from the factory floor to the repair shop. 

How to measure Gloss

The construction of a Glossmeter

A typical glossmeter consists of a fixed mechanical assembly consisting of a standardised light source that projects a parallel beam of light onto the test surface to be measured and a filtered detector located to receive the rays reflected from the surface, Figure 1. The ASTM Method states that the illumination should be defined such that the source-detector combination is spectrally corrected to give the CIE luminous efficiency, V(l), with CIE illuminant SC.

A number of instruments are commercially available that conform to the above standards in terms of their measurement geometry. The instruments are calibrated using reference standards that are usually made from highly polished, plane, black glass with a refractive index of 1.567 for the Sodium D line, and these are assigned a gloss value of 100 for each geometry.

Choosing the correct angle for gloss measurement

Measurement angle refers to the angle between the incident and reflected light. Three measurement angles (20°, 60°, and 85°) are specified to cover the majority of industrial coatings applications. The angle is selected based on the anticipated gloss range, as shown in the following table.

Gloss Range	60° Value	Notes
High Gloss	>70 GU	If measurement exceeds 70 GU, change test setup to 20°
Medium Gloss	10 – 70 GU
Low Gloss	<10 GU	If measurement is less than 10 GU, change test setup to 85°

For example, if the measurement made at 60° is greater than 70 GU, the measurement angle should be changed to 20° to optimise measurement accuracy. Two types of instruments are available on the market: 60° single angle instruments, and one type that combines 20°, 60° and 85°. Two additional angles are used for other materials. An angle of 45° is specified for the measurement of ceramics, films, textiles and anodised aluminium, whilst 75° is specified for paper.

Understanding Gloss units

The measurement scale, Gloss Units (GU), of a glossmeter is a scaling based on a highly polished reference black glass standard with a defined refractive index having a specular reflectance of 100GU at the specified angle. This standard is used to establish an upper point calibration of 100 with the lower end point established at 0 on a perfectly matt surface. This scaling is suitable for most non-metallic coatings and materials (paints and plastics) as they generally fall within this range.
For other materials, highly reflective in appearance (mirrors, plated / raw metal components), higher values can be achieved reaching 2000 Gloss Units. For transparent materials, these values can also be increased due to multiple reflections within the material.

Glossmeter Standards

Comparison of standards for gloss measurement
Standard	20°	60°	85°	45°	75°
	High Gloss	Medium Gloss	Low Gloss	Medium Gloss	Low Gloss
	Coatings, plastics and related materials			Ceramics	Paper
ASTM C346				X
ASTM D523	X	X	X
ASTM C584		X
ASTM D2457	X	X		X
BS3900 D5	X	X	X
DIN 67530	X	X	X
DIN EN ISO 2813	X	X	X
EN ISO 7668	X	X	X	X
JI Z 8741	X	X	X	X	X
TAPPI T480					X

Glossmeter Calibration

Each glossmeter is setup by the manufacturer to be linear throughout its measuring range by calibrating this to a set of master calibration tiles traceable to NIST (National Institute of Standards and Technology).

In order to maintain the performance and linearity of the glossmeter it is recommended to use a checking standard tile.  This standard tile has assigned gloss unit values for each angle of measurement which are also traceable to National Standards such as NIST.  The instrument is calibrated to this checking standard which is commonly referred to as a ‘calibration tile’ or ‘calibration standard’.  The interval of checking this calibration is dependent on the frequency of use and the operating conditions of the glossmeter.

It has been seen that standard calibration tiles kept in optimum conditions can become contaminated and change by a few gloss units over a period of years. Standard tiles which are used in working conditions will require regular calibration or checking by the instrument manufacturer or glossmeter calibration specialist.

A period of one year between standard tile re-calibration should be regarded as a minimum period. If a calibration standard becomes permanently scratched or damaged at any time it will require immediate recalibration or replacement as the glossmeter may give incorrect readings.

International standards state that it is the tile that is the calibrated and traceable artefact  not the gloss-meter, however it is often recommended by manufacturers that the instrument is also checked to verify its operation on a frequency dependent on the operating conditions.

Advances in gloss measurement

The glossmeter is a useful instrument for measuring the gloss of a surface.  However, it is not sensitive to other common effects which reduce appearance quality such as haze and orange peel.

Haze: Caused by a microscopic surface structure which slightly changes the direction of a reflected light causing a bloom adjacent to the specular (gloss) angle. The surface has less reflective contrast and a shallow milky effect

Orange Peel: An uneven surface formation caused by large surface structures distorting the reflected light

Two high gloss surfaces can measure identically with a standard glossmeter but can be visually very different.  Instruments are available to quantify orange peel by measuring Distinctness of Image (DOI) or Reflected Image Quality (RIQ) and Haze.

Gloss meter Applications

The glossmeter is used in many industries from paper mills to automotive and are used by the producer and the user alike.

Examples include:

• Paints & coatings
• Powder coatings
• Additives
• Inks
• Plastics
• Wood coatings, polishes and flooring
• Yacht manufacture
• Automotive manufacture and re-finis
• Aerospace
• Polished stone and metals
• Consumer electronics
• Anodised metals

Wood coatings, polishes and flooring

The gloss of hardwood flooring is typically measured at 60°.

Wood flooring manufacturer’s finishing lines have been using gloss meters for many years to measure the gloss level in quality control (QC) to ensure they always achieve a consistent, quantifiable visual finish.

Gloss Reading	Finish
Up to 20 GU	Low Gloss
21-40 GU	Medium Gloss
41 GU and up	High Gloss

Wood flooring distributors want to check their stock to maintain the integrity of their stock allocation. When wholesale orders are filled from two or more different production runs a gloss meter can verify if the finish of that run is close enough to a preceding run to send out on a job site.

Wood flooring dealers are always comparing the finish of their showroom samples to the actual product they receive from distributors and manufacturers. Gloss meters can help verify a major inconsistency that might impact negatively a project installation later.

Wood flooring installation contractors who perform sand and finish operations on site (site-finishers) need to know the gloss level of the finish type they are using; water-based urethanes, oil-modified urethanes, deep penetrating oil, conversion varnishes, etc.

Wood flooring inspectors get asked occasionally to verify gloss levels from two or more conflicting lots or runs to establish whether or not there was a problem with a previous order fulfillment. Mixing production runs does not always look good to a discriminating consumer with a sharp eye. This happens more often than people realise.

Which industries measure gloss?

How do I select the right angle to measure the gloss of my surface?

ISO 2813 and ASTM D523 (the most commonly used standards) describe three measurement angles for the measurement of gloss across surfaces of all levels.

The standard gloss unit (GU) is used, this is traceable to standards held at NIST.

Universal Measurement Angle- 60º

All gloss levels can be measured using the standard measurement angle of 60º. This is used as the reference angle with the complimentary angles of 85º and 20º often used for low and high gloss levels respectively.

Low Gloss- 85º

For improved resolution of low gloss a grazing angle of 85º is used to measure the surface. This angle is recommended for surfaces which measure less than 10 GU when measured at 60º.

This angle also has a larger measurement spot which will average out differences in the gloss of textured or slightly uneven surfaces.

High Gloss- 20º

The acute measurement angle of 20º gives improved resolution for high gloss surfaces. Surfaces that measure 70 GU and above at the standard angle of 60º are often measured with this geometry.

The 20º angle is more sensitive to haze effects that affect the appearance of a surface.

How can I measure the gloss of curved surfaces?

All standard gloss meters are designed for flat surfaces, if they are used on a curved surface, the measurement beam is reflected away from the instrument detector resulting incorrect readings. The more curved the surface the greater the error.

The solution to this problem is to using a very small area. The light is slightly scattered by the curved surface, however as long as the reflected beam remains sufficiently narrow to remain within the instrument detector the reading will be correct. The Novo-Curve gloss meter has been designed for this purpose and is specified for measuring cylinders and spheres with very low diameters. The Novo-Curve was developed in conjunction with the National Physics Laboratory (NPL).

How can I measure small surface areas?

The Novo-Curve gloss-meter has a very small measurement spot (2mm) that can be used to measure the gloss of very small parts or resolve differences in gloss across small areas.

To get equivalent readings to a standard gloss-meter on surfaces that are slightly irregular it is recommended that the average value is taken of several readings.

These instruments have been used to resolve the gloss differences across holograms, measure the polish on coins, steering wheels and extruded pipe work.

How can I measure irregular surfaces using the Novo-Curve?

When irregular or textured surfaces are measured, the small measurement area can give different gloss values compared to a standard meter that has larger measurement area. To produce comparable results, take 10 measurements on the Novo-Curve gloss meter and use the statistic function to calculate the average reading.

What gloss standard should I be using to measure gloss?

Many industries have adopted the 20/60/85º geometries as specified in ISO2813/ ASTM D523, however consult the table below for more information on specific industries and their industrial standards.

General Gloss measurement

ASTM D523 1999 (USA)

Test method for specular gloss

The principal ASTM specular gloss standard. Very similar to ISO 2813

ASTM D3928 1998 (USA)

Test method for evaluation of gloss or sheen uniformity

ASTM D4039 1999 (USA)

Test method for reflection haze of high-gloss surfaces

ASTM D4449 1999 (USA)

Test method for visual evaluation of gloss differences between surfaces of similar appearance

ASTM D5767 1999 (USA)

Test methods for instrumental measurement of distinctness of image gloss of coating surfaces

ASTM E430 1997 (USA)

Test methods for measurement of gloss of high-gloss surfaces by goniophotometry

MFT 30-064 (South Africa)

Local version of ASTM D523

JIS Z8741 1997 (JAPAN)

Method of measurement for Specular glossiness

Paint

IS0 2813 1994 (International)

Paints and varnishes – determination of specular gloss of non-metallic paint films at 20°, 60° and 85°

The principal ISO specular gloss standard. Very similar to ASTM D523

The following are technically similar to ISO 2813:

BS 3900: Part D5 1995 (UK)

Methods of test for paints – optical tests on paint films – measurement of specular gloss of non-metallic paint films at 20°, 60° and 85°

DIN 67530 1982 (Germany)

Reflectometer as a means for assessing the specular gloss of smooth painted and plastic surfaces

NFT 30-064 1999 (France)

Paints – measurement of specular gloss

at 20, 60 and 85°.

AS 1580 MTD 602.2 1996 (Australia)

Paints and related materials, methods of test – introduction and list of methods.

JIS Z8741 1997 (Japan)

Specular glossiness – Method of measurement.

SS 18 41 84 1982 (Sweden)

Paints and varnishes – measurement of specular gloss of non-metallic paint films at 20, 60 & 85°

Plastics

BS 2782: Pt 5, Method 520A 1992

Methods of testing plastics – optical and colour properties, weathering – determination of specular gloss

Similar to ISO 2813

ASTM D2457 1990

Test Method for Specular Gloss of Plastic Films and Solid Plastics

Specifies the primary standard as a perfect mirror with a defined gloss value of 1000. 20°, 60° and 45°; the 45° method is as ASTM C346 for ceramics.

Metals

BS6161: Part 12 1987

Methods of test for anodic oxidation coatings on aluminium and its alloys – measurement of specular reflectance and specular gloss at angles of 20°, 45°, 60° or 85°

Ref. Std BS 3900: Part D5 (1980); technically equivalent to ISO 7668 replaces BS 1615:1972. At 45°, dimensions of source image and receptor aperture are as for 60°. Squares with sides equal to the shorter sides of the rectangles are also recommended. Alternatively, total reflection in a 45° prism is used as a reference; source image and receptor aperture are then circular, both with angular diameter 3.44° ± 0.23° (1.5 mm ± 0.1 mm at 25.4 mm focal length)

IS0 7668 1986

Anodized aluminium and aluminium alloys – measurement of specular reflectance and specular gloss at angles of 20°, 45°, 60° or 85°.

IS0 5190

Anodizing of aluminium and its alloys – evaluation of uniformity of appearance of architectural anodic finishes – determination of diffuse reflectance and specular gloss

ECCA T2 (European Coil Coating Association)

Specular gloss at 60°.

Paper

DIN 54502 1992

Testing of paper and board; reflectometer as means for gloss Assessment of paper and board

ASTM D1223 1998

Test method for specular gloss of paper and paperboard at 75°.

Has unusual converging beam geometry. Specifies the primary standard as black glass of refractive index 1.540, not 1.567, at the sodium D-line having a defined gloss value of 100.

ASTM D1834 1995

Test method for 20° specular gloss of waxed paper

Another unusual converging beam geometry, different to the previous one.

TAPPI T480 OM-90 1990 (USA)

Specular gloss of paper and paperboard at 75°

Same text as ASTM D 1223

TAPPI 653 1990

Specular gloss of waxed paper and paperboard at 20°

Probably the same text as ASTM D 1834

JIS – Z8142 1993 (Japan)

Testing method for 75° specular gloss

Furniture

BS 3962: Part 1 1980

Methods of test for finishes for wooden furniture – assessment of low angle glare by measurement of specular gloss at 85°

Similar to ISO 2813: 1978

Floor Polish

ASTM D1455 1987

Test method for 60° specular gloss of emulsion floor polish

Ref. std ASTM D 523

Ceramics

ASTM C346 1987

Test method for 45° specular gloss of ceramic materials

Ref. std ASTM D 523

ASTM C584 1981

Test method for 60° specular gloss of glazed ceramic whitewares and related products

Ref. std ASTM D 523 {Sheen}

Fabrics

BS 3424: Method 31: Part 28 1993

Testing coated fabrics – determination of specular gloss

What is a gloss unit?

The measurement scale, Gloss Units (GU), of gloss meters is a scaling based on a highly polished reference black glass standard with a defined refractive index having a specular reflectance of 100GU at the specified angle.

This standard is used to establish an upper point calibration of 100 with the lower end point established at 0 on a perfectly matt surface. This scaling is suitable for most non-metallic coatings and materials (paints and plastics) as they generally fall within this range.

For other materials, highly reflective in appearance (mirrors, plated / raw metal components), higher values can be achieved reaching 2000 Gloss Units when measured at 20°.

What difference in gloss units is visible to the human eye?

If two different coatings are measured, what number of gloss units would be detectable by the human eye, how many units would be perceived as significantly different?

When measuring at 60 Degrees these detectable differences depend on the gloss level of the sample, for instance 3.0 GU difference measured on a very matt surface (perhaps 5GU), would be seen by the human eye but on a higher gloss coating (perhaps 60 GU) the difference would be very difficult to notice.

The only way that you can determine tolerances for your products would be experimentally, perhaps preparing printed samples at different gloss levels that you can show to end users of your coatings or internal “experts”

The other option is to change to a 20/60/85 degree instrument, the 85 degree glossmeter is more sensitive to differences in gloss below 10 GU @ 60º and the 20 Degrees has higher resolution on high gloss coatings (above 70 GU @ 60º). The advantage of using the three angles is that there is more equality to the gloss differences, in our experience a gloss difference of 5 GU, when measured with the correct geometry is just visible to a trained observer.

How to measure the gloss of transparent sheeted materials such as glass or glastic?

It can be problematic to measure the gloss of transparent sheeted material because light is reflected from both the front surface and internally from the second surface.

To only measure reflection from the front surface, the light passing into the material must be absorbed without reflecting from the second surface.

Environmental setup to measure transparent materials with defined backing

An inexpensive standard background to use would be matte black photography wrap that also works almost perfectly at absorbing any light passing through the material.

As any air between the transparent material and the foil will cause the second surface to reflect light, a liquid must be used to optically bond the transparent material to the black foil.

To completely eliminate second surface reflection a liquid with similar refractive index to the test material should be selected. In common practice a drop of water (readily available) or isopropanol (evaporates after measurement) are sufficient to get accurate gloss results for most transparent samples.

If you have any further questions, please feel free to contact us

Why should I send my glossmeter for manufacturer’s recalibration?

As well as calibrating your glossmeter on its own reference gloss tile before use, we recommend that the glossmeter and tile are calibrated yearly by a Rhopoint Approved Service Agent.  This ensures their accuracy, giving you full confidence that your product is performing correctly and that measurements are up-to-date with the best available reference data and compliant to current industry standards.

The primary master gloss artefacts used in our calibrations are calibrated by the National Institute of Standards and Technology (NIST), USA in accordance with the best practices and data available, which are upgraded when appropriate. All of our gloss calibrations are therefore traceable to NIST, with documentation available on request.

What does the calibration process involve?

When the instrument is received, we assess the physical condition and test its basic functions. We then survey the repeatability, accuracy and linearity of the instrument using a minimum of 8 gloss standards. If any major repairs are required, you will receive a quotation at this point before any work is undertaken.

Next, the optic elements and reference gloss tile are cleaned. The glossmeter is then calibrated at a minimum of 8 points throughout the full range of measurement for each angle, with minor adjustments made if required. The reference gloss tile is assigned new values from our master standards or replaced if it is damaged, and an updated certificate is produced.

The calibration date, internal stored calibration values, calibration reference and certification for your instrument are all updated. A report of the as-received readings is also supplied, so that any changes made during the calibration can be tracked and accounted for in a fully-traceable manner.