Appearance is the common situation where surface influences meet visual differences in perception of gloss and color. The impact of different gloss levels does have a great influence on a product as well on its color. The surface quality of a coated surface is often assessed by measuring gloss. Poorly applied coatings or cured paints will show a variety of gloss levels.
Gloss terms are divided in two different groups:
- Focus on the reflected image of an object on the surface
- Focus on the illuminated surface of an objectFocus on reflected image is further divided in:
- Specular gloss
- Image clarity
- DOI (Distinctness of Image)Focus on surface is related to:
- Long-term waviness
- Short-term waviness
Focus on the reflected image obtains information on how distinct the object is reflected and may appear brilliant or diffuse depending on the specular gloss of the surface. If a surface has a high gloss level but seems milky or has a halo around the image of the reflected object than this is an indication of haze. These terms are defined in ASTM E 284 Terminology of Appearance. Gloss measuring instruments are identified by reference to the incidence angles, most 20, 60 and 85° respectively high, medium and low gloss surfaces and expressed in GU (Gloss Units). Alternatively angles of 45 and 75° are used in specific markets.
The visual perception of color changes under influence of gloss. In order to match the color of a product has to be:
Compared by visual means like RAL, NCS or similar standards, or viewed under different light sources in a color-matching booth, or measured using spectrophotometers.
Color depends on three objective aspects:
- Spectral composition (light)
- Spectral reflectance (reflection)
- Spectral response of the eye.
Light is a portion of the electromagnetic spectrum in wavelength between 400 and 700 nm. The lower than 400 nm wavelength is UV and higher than 700 nm wavelength becomes IR. The spectrum colors runs from Blue at 400 nm to Red at 700 nm. The perception of color depends on different light sources and is standardized under CIE Standard Sources and Illuminants.
Generally in terms of D(daylight), A(artificial), TL(fluorescent) and UV(ultra violet). Color measurements are performed using portable systems in field or desktop models in a laboratory situation. Conform CIE values are expressed in Lab and compared Standard against Sample. The visual color difference in DeltaE is a measure to check running color differences during production.
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