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DeGwyn Gems, Private Jewelers since 1975

Sapphire

In all colors other than red, the Sapphire is a variety of Corundum, the mineral group that contains Ruby, Sapphire, and Emery.

DeGwyn Gems, Private Jewelers since 1975
 

History

Classification and Grading

Characteristics of Sapphire

Evaluation

Treatments and Enhancements

Buying a Sapphire, Things to Consider

Bibliography


History

In ancient times, the stones called Sapphires, from the Greek, sapphieros,  probably referred to what we today call Lapis Lazuli. In 1800 it was recognized that both Ruby and Sapphire were in the mineral family Corundum. All colors other than Red of the Corundum gemstone family are considered to be Sapphire. The red variety is called Ruby.

In ancient times, Sapphire was considered endowed with magical properties that would be bestowed on the wearer including truth, authority and protection as well as healing powers.

Large gem quality Sapphires have always been a rare commodity. Some of the more famous Sapphires include the largest, the 563 carat Star of India and the 117 carat Midnight Star at the American Museum of Natural History, New York, and the Star of Asia, a 330 carat Star Sapphire at the Smithsonian Institute.

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Classification and Grading

Sapphire can be defined as opaque, translucent or transparent Corundum. Sapphire denotes all colors of Corundum other than medium to dark red, Ruby. Traditionally Sapphire when not prefixed with a color, meant a blue stone.

Over the years a number of terms and classification nomenclature has been used to describe gem grade Blue Sapphire. These include:

  • Kashmire Sapphire - This term still used today refers to fine 'corn flower' blue stones with a medium transparency.
  • Burmese Sapphire - Finer quality Sapphires have traditionally been called Burmese. These fine grades are characterized by the deep, intense pure blue color with a hint of violet.
  • Thai Sapphire - This term is used primary to describe commercial grade very dark blue stones.
  • Ceylon Sapphire - Stones mined on the island of Sri Lanka, formerly Ceylon are characterized by a bright, lighter shade of blue with strong brilliance and with gray or violet shading.
  • African Sapphire - Characterized by lighter shades and pastels.

All Sapphires colored other than blue are usually referred as Green Sapphire, Yellow Sapphire, etc. Virtually all colors are represented in the Sapphire family of Corundum.

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Characteristics of Sapphire

  • Chemical Composition - Aluminum Oxide, Al2O3
  • Crystallography - Hexagonal System characterized by six sided prisms terminated by flat faces.
  • Hardness - 9 on the Moh's Hardness Table
  • Cleavage - None
  • Fracture - Conchoidal, splinter, brittle
  • Characteristic inclusions - Sapphire often contains rutile or negative crystals, called "Silk." These are often found arranged in three sets of intersecting lines that are instrumental in stones that display asterism. Other commonly found mineral inclusions are Zircon, Mica, and Spinel.
  • Fluorescence - none

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Evaluation

As with most colored gemstones, color is the most important element. Sapphire is noted for banding and parallel plane striation. Although Sapphires exhibiting this layered striation can be cut in such a way as to appear well colored when viewed from above, this color banding severely effects value.

Fine qualities of Blue Sapphire should have a pure and intense blue color, neither pale or very dark,  with little or no undertones of purple or gray. As with Ruby,  the vast majority of stones, once cut, display inclusions, silk, clouds or uneven color distribution. Sapphires that are flawless under 10X are extremely rare and most stones show some level of imperfection. 

Cutting style and quality have significant bearing on value as the depth of stone contributes greatly to the overall appearance of a stone's color saturation. In addition the orientation to the original crystal structure has dramatic effect on the resulting color display.

Evenness of color, lack of surface imperfections, quality of final polish and symmetry are important in the overall evaluation of fine Sapphires as well and are important to the final evaluation of any stone.

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Treatments and Enhancements

The most common treatments and enhancements of Sapphire are:

  • Heat Treatment - rough stone is heated to very high temperature resulting in usually permanent enhancement of color
  • Dyes, laminates and impregnated waxes are sometimes seen but are not permanent and should be avoided.

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Buying a Sapphire, Things to Consider
 

There are three elements that should be considered when buying a Sapphire.

Color - Look for intense pure color, neither dark or pale. Striping and uneven coloration is common in lower quality stones and should be avoided.

Clarity - Inclusions are very common and their size and location should be carefully considered. Rutile crystal inclusions are referred to as Silk and when evenly distributed can produce a sheen in transparent Sapphires and the asterism seen in Star Sapphires.

Cut - Sapphires are often cut in their countries of origin. Many of these stones were cut with emphasis on creating the heaviest stone from the rough crystal instead of cutting for the beauty achieved with proper proportion and orientation. Although Sapphire is the next hardest stone to Diamond, surface imperfections such as pitting and striation should be at a minimum. Finally an even finish polish and quality of facet placement and symmetry should be considered.

Sapphire prices have increased dramatically over the last few years  Fine stones today can command per carat prices that are comparable to Diamond prices.

Because of its hardness, Sapphire can be safely used in all types of jewelry including rings and bracelets and unlike more brittle stones, such as Emerald, can be safely bezel mounted.

Bibliography

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