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Information about Gloss (material Appearance)

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Gloss is an optical property, which is based on the interaction of light with physical characteristics of a surface. It is actually the ability of a surface to reflect light into the specular direction. The factors that affects gloss are the refractive index of the material, the angle of incident light and the surface topography.

Gloss can be said as a view of material appearance. Materials with smooth surfaces appear glossy, while very rough surfaces reflect no specular light and therefore appear matt (British English) or matte (American English). Gloss is also expressed as lustre (mineralogy) or sheen in certain fields of application.

Qualitative and Quantitative View of Gloss

Surface gloss is considered to be the amount of incident light that is reflected at the specular reflectance angle of the mean of that surface. So, specular gloss is proportional to the reflectance of the surface.

The Fresnel formula gives the specular reflectance, , for an unpolarized light of intensity , at angle of incidence , giving the intensity of specularly reflected beam of intensity , while the refractive index of the surface specimen is .

The Fresnel equation is given as follows :

Surface Roughness

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Figure1:Specular reflection of light from a rough surface
Surface roughness in micrometer range influences the specular reflectance levels. The diagram on the right depicts the reflection at an angle on a rough surface with a characteristic roughness height . The path difference between rays reflected from the top and bottom of the surface bumps is:



When the wavelength of the light is , the phase difference will be:



If is small, the two beams (see Figure 1) are nearly in phase and therefore the specimen surface can be considered smooth. But when , then beams are not in phase and through interference, cancellation of each other will occur. Low intensity of specularly reflected light means the surface is rough and it scatters the light in other directions. If an arbitrary criterion for smooth surface is , then substitution into the equation above will produce:



This smooth surface condition is known as the Rayleigh criterion.

Gloss Measurement

Specular reflection is measured with a specular glossmeter. Unpolarised white light is concentrated by a condenser lens onto a field aperture, which is located in the focal plane of the source lens. The reflected beam at the surface is later collected by the receptor lens. The intensity of the beam is then measured through a photodetector.

The common angles of incidence for gloss measurement are 20°, 60° and 85°. In some cases is used 45° and 75° geometry. Low gloss surfaces are recommended to be measured with 85° settings.

The typical standards for gloss measurements are ASTM D 2457, DIN EN ISO 2813 and DIN 67530.

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Glossmeter

References

  • Meeten, G.H. (1986). Optical Properties of Polymers. London: Elsevier Applied Science, 326-329. ISBN 0-85334-434-5. 
Optics (ὀπτική appearance or look in Ancient Greek) is a branch of physics that describes the behavior and properties of light and the interaction of light with matter.
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Specular reflection is the perfect, mirror-like reflection of light (or sometimes other kinds of wave) from a surface, in which light from a single incoming direction (a ray) is reflected into a single outgoing direction.
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Topography (Greek topos, "place", and graphia, "writing") is the study of Earth's surface features or those of planets, moons, and asteroids.

In a broader sense, topography is concerned with local detail in general, including not only relief but also
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British English (BrE, BE, en-GB) is the broad term used to distinguish the forms of the English language used in the United Kingdom from forms used elsewhere in the Anglophone world.
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American English (AmE, AE, AmEng, USEng, en-US), also known as United States English or U.S. English, is a set of dialects of the English language used mostly in the United States.
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For other senses of this word, see lustre.


Lustre (American English: luster) is a description of the way light interacts with the surface of a crystal, rock, or mineral.
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In optics and heat transfer, reflectivity is the fraction of incident radiation reflected by a surface. In full generality it must be treated as a directional property that is a function of the reflected direction, the incident direction, and the incident wavelength.
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Augustin-Jean Fresnel (pronounced [freɪ'nel] in AmE (or fray-NELL), [fʁɛ'nɛl
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In physics, intensity is a measure of the time-averaged energy flux. To find the intensity, take the energy density (that is, the energy per unit volume) and multiply it by the velocity at which the energy is moving. The resulting vector has the units of power divided by area (i.e.
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Augustin-Jean Fresnel (pronounced [freɪ'nel] in AmE (or fray-NELL), [fʁɛ'nɛl
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Condenser may refer to:
  • Condenser (laboratory), a range of laboratory glassware used to remove heat from fluids.
  • Abbe condenser, a group of lenses mounted below the stage of an optical microscope to concentrate light.

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In optics, an aperture is a hole or an opening through which light is admitted. More specifically, the aperture of an optical system is the opening that determines the cone angle of a bundle of rays that come to a focus in the image plane.
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A standards organization, also sometimes referred to as a standards body, a standards development organization or SDO (depending on what is being referenced), is any entity whose primary activities are developing, coordinating, promulgating, revising, amending,
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ASTM International (ASTM) is an international standards developing organization that develops and publishes voluntary technical standards for a wide range of materials, products, systems, and services.
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DIN or Din or din can have several meanings:-
  • A din is a loud noise.
  • Dīn, an Arabic term meaning "religion" or "way of life".
  • Din (Kabbalah) is one of the ten aspects of the Ein Sof in Kabbalah (more commonly known as "Gevurah").

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