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| an effect in the brain produced by reaction to visible light that reaches the back of the eye; the reaction triggers messages to the brain and color is 'seen'; most color is perceived after modification of white light |
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electromagnetic radiation energy having wavelengths of between 400nm and 700nm, which is detected by human eyes
because we normally use our eyes to detect light radiation, light provides the most convenient means for various methods of testing and identifying most gem materials (optical testing) |
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| lacking of color response to certain wavelengths of visible light |
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| chemical elements within a material that are capable of causing selective absorption of visible light |
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| body color in a gemstone is derived from the visible light in which it is viewed, the absorption by the gemstone of some of the color spectrum (i.e. certain wavelengths) from that light, and our perception of the residual light |
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| the splitting of white light into the ocmponent colors of the visible light spectrum whereby each wavelength is refracted at a differing angle; the measured amount of dispersion in a gemstone is the difference in refractive index of light measured at two different selected wavelengths |
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| a popular term for the spectral colors displayed by a gemstone with a significant degree of dispersion |
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| a 'spreading' effect upon light that occurs when light waves pass an edge, pass through thin slits or very small holes; it can cause interference in white light to produce iridescence |
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| type of grid of parallel slits or parallel lines imprinted on a transparent sheet that cause the diffracted waves to interfere in a systematic way to produce spread-out spectra |
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| visible light is absorbed when electrons in a material interact with the light to convert it into visible heat energy; this light is therefore not transmitted all the way through the material |
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| a pattern of dark bands or lines in the visible light spectrum, seen when light from certain gem materials is viewed thorugh a spectroscope |
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| an instrumen which separates a ray of light into its constituent wavelengths or spectrum colors by means of prisms or a diffraction grating, enabling observation of the color or colors making up a ray of light |
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| Diffraction Grating Spectroscope |
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| a diffraction 'grating' consisting of very fine, closely-spaced parallel lines printed or engraved on a glass, plastic or metal plate is used to produce an observable spectrum in this type of spectroscope |
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| several glass prisms, cemented together in line, are used to produce an observable spectrum in this type of spectroscope |
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| transparent material with a particular selective absorption which is used to view the body colors of gem materials; the overall selective absorption through both the filter and the gem material may differ for different gem materials with the same body color, allowing the gem materials to be distinguished |
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| occurs when, upon illuminating certain stones with two slightly differing incident 'white' light sources, different color sensatiosn are produced in the brain |
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a differential selective absorption of light by certain anisotropic colored materials; the term is used to describe the different colors which may be seen in different directions in certain colored gemstones
Dichroism - two colors
Trichroism - three colors |
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an instrument for detecting pleochroism in a material
using either a calcite crystal or polarizing filters, it is constructed so that two pleochroic colors, or shades of color, may be detected and compared side by side in a single view |
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"play of color"
a color, or series of colors, produced by interference or diffraction when visible light is reflected or diffracted from thin layers or from the internal structures of gems such as labradorite or precious opal |
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| allochromatic materials owe their body color to the presence of certain chemical elements which do not form an essential part of the chemical composition of the material |
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| idiochromatic materials are those which owe their body color to elements that are an essential part of the chemical composition of the material |
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| pleochroism in uniaxial crystal structures through which the two princiapl vibration directions show a differing color or shade of color |
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| the pleochroism of those optically biaxial gemstones which have differential selective absorption in the three principal vibration directions giving three principal body color variations |
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a convenient unit of length measurement used for electromagnetic radiations
one nanometer (1nm) is one billionth of a meter 10-9m
unit of length for light wavelength |
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| the absorption by a material of only certain wavelengths of light |
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| the name given to a range of frequencies or wavelengths or radiation |
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when light waves can pass through a material without being completely absorbed, they are said to be transmitted
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| a description of a cycle of energy transmission |
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| a combination of all frequencies (wavelengths) of visible light, as from the sun |
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| a solid, transparent, singly-refracting material shaped in order to transmit light to produce, for example, dispersion or reflection |
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