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The art of cutting a gem is an exacting procedure performed on a faceting machine.The ideal product of facet cutting is a gemstone that displays a pleasing balance of internal reflections of light known as brilliance, strong and colorful dispersion which is commonly referred to as "fire", and brightly colored flashes of reflected light known as scintillation.
Asterism is generated by reflections of light from twin-lamellae or from extremely fine needle-shaped acicular inclusions within the stone's crystal structure. [1] A common cause is oriented sub-microscopic crystals of rutile within the gem mineral. It occurs in rubies, sapphires, garnet, diopside, and spinel when a cabochon is cut from a ...
The Syrian rhetorician Lucian (c. 125–180 CE) describes a statue of the Syrian goddess Atargatis in Hierapolis Bambyce (present-day Manbij) with a gem on her head called Greek lychnis (λύχνος, "lamp; light") (Schafer 1963: 237). "From this stone flashes a great light in the night-time, so that the whole temple gleams brightly as by the ...
The word traces its origins back to the Latin lux, meaning "light", and generally implies radiance, gloss, or brilliance. A range of terms are used to describe lustre, such as earthy, metallic, greasy, and silky. Similarly, the term vitreous (derived from the Latin for glass, vitrum) refers to a glassy lustre. A list of these terms is given below.
One test to determine the gem's identity is to measure the refraction of light in the gem. Essentially, when light passes from one medium to another, it bends. Blue light bends more than red light. How much the light bends will vary depending on the gem mineral. Every material has a critical angle, above which point light is reflected back ...
Gem-quality material is usually a strong yellow to honey brown, orange, red, or green; its very high RI (2.37) and dispersion (0.156) make for an extremely lustrous and fiery gem, and it is also isotropic. But here again, its low hardness (2.5–4) and perfect dodecahedral cleavage preclude sphalerite's wide use in jewelry.
In a further study published in 2017, the team collaborated with Hillar Aben, a professor at Tallinn University of Technology in Estonia using a transmission polariscope to measure the optical retardation of light from a red LED as it travelled through the glass drop, and used the data to construct the stress distribution throughout the drop ...
It has been speculated that the sunstone (Old Norse: sólarsteinn, a different mineral from the gem-quality sunstone) mentioned in medieval Icelandic texts, such as Rauðúlfs þáttr, was Iceland spar, and that Vikings used its light-polarizing property to tell the direction of the sun on cloudy days for navigational purposes.