Shine

Diffuse and specular reflection of light from the surface

Glare on the surface of polished glass balls due to specular reflection

Gloss (brilliance) is an optical characteristic of the property of a surface that reflects light , showing the relationship between the intensities of light , specularly reflected from the surface, and light scattered in all directions — diffuse reflection .

Content

Nature of the Phenomenon

Bleskomer

Gloss is due to the specular reflection of light from the surface, most of which occurs simultaneously with diffuse reflection. The human eye perceives specular reflection together with diffuse. A quantitative estimate of the brightness is determined by the ratio between the intensities of specularly and diffusely reflected light. In mineralogy, shine is characterized by qualitative attributes ( shine of minerals ).

Subjective brilliance depends not only on the smoothness of the surface, but also on the reflection coefficient.

Smooth surface. If the size of surface irregularities is much smaller than the wavelength, then the proportion of specularly reflected light with respect to diffuse is large. If the size of the surface irregularities is comparable or much larger than the wavelength (rough surface), then the proportion of diffusely reflected light is large.
Reflection coefficient The reflection coefficient is the ratio of the intensity of the reflected light to the intensity of the incident light.

Reflection from smooth surfaces

Mirror reflection coefficient $K_{r}$ ${\ displaystyle K_ {r}}$ expressed as:

K_{r}={\frac {I_{r}}{I_{0}}},

{\ displaystyle K_ {r} = {\ frac {I_ {r}} {I_ {0}}},}

Where

I_{r}

{\ displaystyle I_ {r}}

- intensity of the reflected light;

Where

I_{0}

{\ displaystyle I_ {0}}

- The intensity of the incident light.

All metals in a compact form reflect light well, and if the metal surface is smooth, then a mirror image is observed. With an increase in the surface roughness of the metal, the diffuse reflection increases.

Smooth transparent dielectrics also mirror the light, but partly the light penetrates into the dielectric and the specular reflectance of such substances is always less than the specular reflectance of metals, and the reflectance depends on the angle of incidence of light on the surface and on the refractive index of the substance.

The reflection coefficient of dielectrics is expressed by the Fresnel formula :

K_{r}={\frac {1}{2}}\left[\left({\frac {\cos \phi -{\sqrt {n^{2}-\sin ^{2}\phi }}}{\cos \phi +{\sqrt {n^{2}-\sin ^{2}\phi }}}}\right)^{2}+\left({\frac {n^{2}\cos \phi -{\sqrt {n^{2}-\sin ^{2}\phi }}}{n^{2}\cos \phi +{\sqrt {n^{2}-\sin ^{2}\phi }}}}\right)^{2}\right],

{\ displaystyle K_ {r} = {\ frac {1} {2}} \ left [\ left ({\ frac {\ cos \ phi - {\ sqrt {n ^ {2} - \ sin ^ {2} \ phi}}} {\ cos \ phi + {\ sqrt {n ^ {2} - \ sin ^ {2} \ phi}}}} \ right) ^ {2} + \ left ({\ frac {n ^ { 2} \ cos \ phi - {\ sqrt {n ^ {2} - \ sin ^ {2} \ phi}}} {n ^ {2} \ cos \ phi + {\ sqrt {n ^ {2} - \ sin ^ {2} \ phi}}}} \ right) ^ {2} \ right],}

Where

n

{\ displaystyle n}

- refractive index;

\phi

{\ displaystyle \ phi}

- the angle of incidence of light.

Thus, the higher the refractive index, the higher the brilliance of a substance, for example, a diamond has a high refractive index, about 2.42 and therefore a high gloss, and the water has a refractive index of about 1.33 and the water droplets glitter slightly.

Gloss classification

For paint coatings

Degree of gloss,%, for coatings
Degree of shine	Limits
Degree of shine	lower limit	Upper limit
Deep matt	0	3
Matt	four	nineteen
Semi-matt	20	36
Semi-glossy	37	49
Glossy	50	59
High gloss	59	100

The degree of gloss coatings on the example of samples of paper-laminated plastic
Matt (right)
Semi-matt
Semi-gloss (left)
Glossy (right)

Objective measurement of the gloss of paintwork and other surfaces, for example, the surface of polymers and polymer coatings is performed using a photoelectric gloss meter ^[1] . This device determines the proportion of reflected light compared to the standard of quartz or black polished glass, the brightness of which is conventionally assumed to be 100% or 100 units ^[2] ^[3] .

For minerals

In mineralogy, the brilliance of minerals is qualitatively classified by the following characteristics:

Glass shine - characteristic of substances with a low refractive index. For example, quartz , calcite , feldspar , fluorite , etc. The gloss is similar to the gloss of glass.
Metallic luster - is observed in native metals , but some minerals with relatively low electrical conductivity , such as pyrite , chalcopyrite , galena, also have a metallic luster, similar to the luster of the metal, due to the presence of relatively free electrons in the crystal lattice.
Semi-metallic luster - dull, metallic. Examples are graphite , crystalline iodine .
Diamond shine - looks like a bright glass shine, characteristic of minerals with a high refractive index ^[4] . Examples are diamond , sphalerite , rutile , zircon .
Bold shine - not bright, not very noticeable. Looks like a shine of fat, fat. An example is native sulfur .

Special types of gloss

Pearl, diverse in appearance. An example is mica .
Silky. Glitter threadlike crystalline fibers. Examples are selenite , asbestos .
Matt - almost no gloss, for example, chalk .

Examples of different types of gloss for minerals
Hematite
Metallic luster
Sphalerite
Diamond shine
Malachite and Chrysolite compounds
Bold shine
Quartz
Glass shine
Prith
Pearlescent shine
Eye of the Tiger
Silky sheen
Stolzit
Semi-gloss or wax gloss
Aluminum Matt

Notes

↑ GOST 896-69 Paint materials. Photoelectric gloss method.
↑ GOST 9.032-74 Paint coatings. Groups, technical requirements and designations.
↑ GOST 31975-2013 (ISO 2813: 1994) Paint materials. Method for determining the gloss of paint coatings that do not have a metallic effect at an angle of 20, 60 and 85
↑ Kulikov B. F., Bukanov V. V. The dictionary of gem stones, Leningrad, “Nedra”, 1988, p. 25.

Links

Brilliance of Mineral (rus.)

[1] GOST 896-69 Paint materials. Photoelectric gloss method.

[2] GOST 9.032-74 Paint coatings. Groups, technical requirements and designations.

[3] GOST 31975-2013 (ISO 2813: 1994) Paint materials. Method for determining the gloss of paint coatings that do not have a metallic effect at an angle of 20, 60 and 85

[4] Kulikov B. F., Bukanov V. V. The dictionary of gem stones, Leningrad, “Nedra”, 1988, p. 25.

Shine

Content

Nature of the Phenomenon

Reflection from smooth surfaces

Gloss classification

For paint coatings

For minerals

Special types of gloss

Notes

Links

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