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Coatings Ingredients
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Coatings Ingredients

Glossy Finish: Basics and Gloss Control in Paints and Coatings

Glossy Paints
  1. What is Gloss?
  2. Light Reflectance by Different Types of Paint Finishes
  3. Glossy Paints – Composition & Properties
  4. Factors to Achieve Gloss Enhancement and Retention in Coatings
  5. Popular Standards to Measure Gloss of Paints & Coatings


What is Gloss?


The final finish of a coated surface has been recognized as prime importance for both the formulator as well as the consumer. There is no doubt that the paint finish can make a huge difference with respect to the overall appearance of the surface.

It is the optical properties of paint or simply say interaction of light with the components of paints (pigments, binders, etc.) that allow us to sense its finish (glossy or matt), thickness, color, and opacity. When light is incident on the painted surface, it gets reflected, absorbed, and transmitted by the paint film.

Gloss is a function of light reflection – the more light is reflected, the glossier the surface appears to be. While a matt surface scatters the light in many directions and the surface appears less glossy. The measure of the ability of the paint film to reflect light is called gloss. The gloss of different surfaces and paint film is different.

The higher the gloss of the paint film, the stronger its ability to reflect light and the higher the brightness. 

Let's explore the amount of light reflected by various paint finishes along with the key properties, factors and test standards required to obtain glossy surfaces.


Light Reflectance by Different Types of Paint Finishes


Paint finish (or sheen) refers to the amount of light that the paint reflects from its surface. The most common categories of paint finish are matt and gloss with a wide range of variants between the two, ranging from dull to shiny.

  • Flat or matt paints absorb more light than they reflect due to rough surface, so they have no sheen.
  • Semi-gloss and gloss paints reflect light, giving them a bright, shiny finish. They deliver exceptionally smooth surfaces with few microscopic irregularities.

In a 1930s publication by the Journal of Research of the National Bureau of Standards, “gloss” is defined as the surface light-reflecting properties and “glossiness” as the appearance resulting from the surface’s power to reflect light.

Different types of finishes along with the percentage of light reflectance are mentioned in the table below.

Paint Finish Description
Full Gloss
Type: Full gloss
Light Reflectance: 70% - 90% 
Description: Shows clear specular reflection at all angles of view
Semigloss
Type: Semi gloss
Light Reflectance: 41% - 69%
Description: Shows specular reflection when viewed at low angles to the surface but only a hazy reflection at higher angles
Sheen Finish
Type: Sheen & Satin
Light Reflectance: 15% - 40%
Description: Shows partial reflection of light
Eggshell Finish
Type: Eggshell
Light Reflectance: 10% - 15%
Description: Shows hazy reflection for all angles of view with clear specular reflection near grazing incidence
Matt Finish
Type: Matt
Light Reflectance: <10%
Description: Shows no specular reflection even at grazing incidence


Glossy Paints – Composition & Properties


Gloss coatings consist of the resins that will become the final coating, pigments, and other additives dissolved in some compatible solvent blend.

  • The resins may be very viscous liquids or even solids by themselves.
  • The solvents reduce the viscosity and aid the surface leveling of the coating.
  • The additives are added to impart durability, moisture resistance and some of them impart shine or dullness finish.

A gloss finish, as it dries, leaves a surface that is smooth within a small fraction of a wavelength of light.

Paints with glossier finishes, like satin paint, have higher levels of resin and lower levels of pigmentation. High resin quantities allow the paint to flow more smoothly and evenly than low resin paints. High resin quantities keep pigment particles low and embedded within the resin, which gives the painted surface a strong glossiness.

Properties of Glossy paints:

  • They have a highly reflective sheen.
  • They are very durable and stable, easy to clean and maintain.
  • They exaggerate imperfections on surfaces.
  • They are a good choice for surfaces that need frequent cleaning.

On the opposite end of the scale are flat (matt) paints that reduce glare and hide imperfections in the surface and finish.

Matting in Paints and Coatings


Factors to Achieve Gloss Enhancement and Retention in Coatings


As we discussed above, the glossy aspect of paint is due to a high reflectivity of the surface of the paint film and it is strongly related to the application area (car body, kitchen, doors, etc.) it is intended to be used.

Let us mention the factors which affect the glossiness of paints surface and how these factors can be optimized to achieve the desired coating gloss.


Surface Roughness & Surface Modifying Additives


Gloss is a function of roughness and can be used to characterize surface roughness. The smaller the roughness of the surface of the object, the more light is reflected and the higher the gloss. On the contrary, if the surface of the object is uneven, the amount of light scattered is increased, resulting in a decrease in gloss.

Surface modifying additives help to enhance gloss by:

  • Helping the paint to level out after application, and
  • Increasing pigment dispersion

There are specialty surfactants and leveling agents designed to enhance paint leveling and thus, act as a gloss enhancer.

Pigments are also used to vary the surface roughness in an attempt to increase or decrease gloss. The protrusion of pigments causes the reflected light to scatter resulting in low gloss.


Quantity and Particle Size of Pigment


Pigments: Types & SelectionWhen it comes to pigment, the three factors can affect the gloss of the coating film. They include:

  • Quantity and concentration of pigment in the formulation
  • The dispersibility of pigment
  • The particle size and particle size distribution

The two main concepts governing the quantity of pigments during coating formulation process are:

  • Pigment volume concentration (PVC)
  • Pigment to binder ratio (P:B)

On one hand, PVC is of fundamental concern when formulating paints that are needed to have an optimum performance with respect to durability. On the other hand, the P:B ratio, by weight or occasionally by volume, is often used for balancing a formulation for gloss and opacity.

For systems requiring high gloss, low PVC is required, while primers and undercoats can have much higher PVC - up to 90% because they need to be more durable and flexible.

The pigment particle size and particle size distribution are other crucial factors affecting the gloss of the coating. Particle size is related directly to the efficiency with which a pigment scatters light, with the scattering power increasing as particle size decreases. Small particles produce uniform and glossier coatings, where the angle of incident light is close to the angle of reflected light.

The ability of a given pigment to absorb light (tinctorial power) increases when the diameter of the particles is reduced and consequently by increasing the specific surface until the size at which the particles become transparent to incident light is attained. For example, in the case of titanium oxide (TiO2) the optimal size required is close to 1 µm.


Popular Standards to Measure Gloss of Paints & Coatings


Gloss is measured using a glossmeter. It is determined by measuring the percent reflectance using a simple photodetector arranged so that the illumination and detection occur at equal and opposite angles.

Gloss is measured on a scale from ‘0’ to ‘100’, with ‘0’ being no gloss and ‘100’ being perfectly mirror-like. These gloss levels are measured at different angles i.e. 20°, 60° or 85° depending on the gloss level to be achieved. This is based on the angle of sight that these paints would normally be seen.

For example, flat paints are measured at 85° as they are often used on the ceiling. Whereas gloss paints are measured at 20°, as they are normally seen straight on (e.g. doors).

Paint Type Gloss Units (GU) Degree of Gloss Measurement 
Ultra-Flat ≤1 85°
Flat 1-2 85°
Matt 3-7 60°
Low Sheen 8-12 60°
Satin 20-30 60°
Gloss 40-80 20°
High Gloss  > 80 20°


Different Kinds of Gloss measured as the Reflected Radiance
Different Kinds of Gloss measured as the Reflected Radiance at Specific Incident and Outgoing Directions
© Central European Journal of Physics


Different Gloss Standards include:

  • ISO 2813 2000 (International) Paints and varnishes – Determination of specular gloss of non-metallic paint films at 20°, 60° and 85° The principal ISO specular gloss standard.
  • ASTM D523 - 14 (2018) Standard Test Method for Specular Gloss

The following are technically similar to above mentioned standards:

  • 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°


Commercially Available Gloss Control Agents for Paints  



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