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Sapphire by crylight

Natural sapphire

Sapphire is one of the two gem varieties of corundum, the other being the red ruby. Although blue is the most well known hue, sapphire is any color of corundum except red. Sapphire may also be colorless, and it also occurs in the non-spectral shades gray and black. Pinkish-orange sapphire is known as padparadscha. The cost of natural sapphire varies depending on their color, clarity, size, cut, and overall quality as well as geographic origin. Significant sapphire deposits are found in Eastern Australia, Thailand, Sri Lanka, Madagascar, East Africa and in the United States at various locations (Gem Mountain) and in the Missouri River near Helena, Montana. [1] Sapphire and rubies are often found together in the same area, but one gem is usually more abundant.[2]

Blue sapphire

Color in gemstones breaks down into three components: hue, saturation, and tone. Hue is most commonly understood as the "color" of the gemstone. Saturation refers to the vividness or brightness or "colorfulness" of the hue, and tone is the lightness to darkness of the hue. [3] Blue sapphire exists in various mixtures of its primary and secondary hues, various tonal levels (shades) and at various levels of saturation (brightness): the primary hue must, of course, be blue.

Blue sapphires are evaluated based upon the purity of their primary hue. Purple, violet and green are the normal secondary hues found in blue sapphires. [4] Violet and purple can contribute to the overall beauty of the color, while green is considered a distinct negative. [4] Blue sapphires with no more than 15% violet or purple are generally said to be of fine quality. [4] Blue sapphires with any amount of green as a secondary hue are not considered to be fine quality.[4] Gray is the normal saturation modifier or mask found in blue sapphires.[4] Gray reduces the saturation or brightness of the hue and therefore has a distinctly negative effect.

The color of fine blue sapphires can be described as a vivid medium dark violet to purplish blue where the primary blue hue is at least 85% and the secondary hue no more than 15% without the least admixture of a green secondary hue or a gray mask. [3] The 422.99 carats (84.60 g) Logan sapphire in the National Museum of Natural History, Washington D.C. is one of the largest faceted gem-quality blue sapphires in the world.

Source of Color Sapphire

Red rubies are corundum which contain chromium impurities that absorb yellow-green light and result in deeper ruby red color with increasing content.[5] Purple sapphires contain trace amounts of vanadium and come in a variety of shades. Corundum that contains ~0.01% of titanium is colorless. If trace amounts of iron are present, a very pale yellow to green color may be seen. If both titanium and iron impurities are present together, however, the result is a magnificent deep-blue color.

Unlike localized ("interatomic") absorption of light which causes color for chromium and vanadium impurities, blue color in sapphires comes from intervalence charge transfer, which is the transfer of an electron from one transition-metal ion to another via the conduction or valence band. The iron can take the form Fe2+ or Fe3+, while titanium generally takes the form Ti4+. If Fe2+ and Ti4+ ions are substituted for Al3+, localized areas of charge imbalance are created. An electron transfer from Fe2+ and Ti4+ can cause a change in the valence state of both. Because of the valence change there is a specific change in energy for the electron, and electromagnetic energy is absorbed. The wavelength of the energy absorbed corresponds to yellow light. When this light is subtracted from incident white light, the complementary color blue results. Sometimes when atomic spacing is different in different directions there is resulting blue-green dichroism. Intervalence charge transfer is a process that produces a strong colored appearance at a low percentage of impurity. While at least 1% chromium must be present in corundum before the deep red ruby color is seen, sapphire blue is apparent with the presence of only 0.01% of titanium and iron.

Fancy color sapphire

Purple sapphires are lower in price than blue ones. Yellow and green sapphires are also commonly found. Pink sapphires deepen in color as the quantity of chromium increases. The deeper the pink color the higher their monetary value as long as the color is going toward the red of rubies. Sapphires also occur in shades of orange and brown, and colorless sapphires are sometimes used as diamond substitutes in jewelry. Salmon-colored padparadscha (see below) sapphires often fetch higher prices than many of even the finest blue sapphires. Recently, sapphires of this color have appeared on the market as a result of a new treatment method called "lattice diffusion".[citation needed]

Padparadscha

Padparadscha is a pinkish-orange to orangy-pink colored corundum, with a low to medium saturation and light tone, originally being mined in Sri Lanka, but also found in deposits in Vietnam and Africa. Padparadscha sapphires are very rare, and highly valued for their subtle blend of soft pink and orange hues. The name derives from the Sinhalese word for lotus blossom. Along with rubies they are the only corundums to be given their own name instead of being called a particular colored sapphire. Cut stone Padparadscha The rarest of all padparadschas is the totally natural variety, with no beryllium or other treatment, and no heating. To find a stone that is certified by a reputable lab as being completely natural is extremely rare and the stone will be very expensive. High quality, unheated and untreated natural padparadscha sapphires will start off in the range of $5,000 per carat and rise by size, color, tone, cut, and clarity, to $20,000–30,000 per carat.

Color change sapphire

A rare variety of sapphire, known as color change sapphire, exhibits different colors in different light. Color change sapphires are blue in outdoor light and purple under incandescent indoor light. Color changes may also be pink in daylight to greenish under fluorescent light. Some stones shift color well and others only partially, in that some stones go from blue to bluish purple. While color change sapphires come from a variety of locations, the gem gravels of Tanzania is the main source. Certain synthetic color-change sapphires are sold as “lab” or “synthetic” alexandrite, which is accurately called an alexandrite simulant (also called alexandrium) since the latter is actually a type of chrysoberyl---an entirely different substance whose pleochroism is different and much more pronounced than color-change corundum (sapphire).

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