9/14/2023 0 Comments Corundum ruby sapphireCrystal morphology (crystal shape) is closely related to crystal growth. The growth lines (picture 1.2.1) in the natural crystals (including corundum) are straight and follow the directions of the crystal flat faces of the raw material before the faceting. Their color is known as “pigeon blood” (picture 1.1.3). Ruby may exhibit one of a few possible secondary hues – pink, purple and orange. Most desirable and expensive are the rubies with light purple hue and tone 8. Blue color tones from 5 to 9 in natural jewelry blue sapphires The blue color tones from 5 to 9 for natural jewelry blue sapphires are shown in picture 1.1.2 from left to right. Most desired blue color tone for corundum is 8. When defining the color and color tone, the stones should be placed on a clean white paper with the pavilion facets up, as the dispersion from the crown facets can mislead us. Picture 1.1.1 Different colors in natural corundum The red corundum with a color tone of over 5 is called ruby, and corundum of all other colors – sapphire (white sapphire, yellow sapphire, orange sapphire, pink sapphire, blue sapphire, green sapphire, etc.). Saturation refers to the intensity of color and is the degree to which color departs from a neutral (gray) sensation. The tone scale is divided into 11 grades, 0 to 10, with 10 being black. Natural corundum can be found in all colors in nature with a wide variety of hue, tone, and saturation (according to the GIA grading system for colored gemstones) (picture 1.1.1). The color is determined with hue precision, for example, red-violet, violet, violet-blue, etc. Tone refers to a gem’s relative lightness or darkness of color, for example extremely light, very light, light. 1.1 Color, tone, and hue in natural corundum.
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