Colour concentration may be seen arround melted guest crystal. Most melted crystals are surrounded by discoid fractures often with dendritic pattern (partial recrystallization) they often show a cottony appearence. Resulting inclusions are distorted melted guest crystals such as white formless zircon (often with gas bubble). Very high heat treatment is required to diffuse the colouring agent into the gem. Other colours may also result or be improved by this treatment (typically ruby, blue and green sapphires): standard tests are limited especially for clean light gems. In most cases, unlike natural, the rays do not show a 90° orientation to color zoning (crystal faces).ĭiffusion (beryllium): Most corundum with orangy hue, strong bi-coloration and saturated colours, typically yellow, orange, red-orangy, orangy-pink, pink-purple, hot pink, and padparadscha colour are beryllium treated. Fiber-optic light: shallow fuzzy whitish surface layer. Star-diffusion(titanium): Surface-diffusion on a gem already cut into cabochon shape: strong star effect occuring at and just below the surface.
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