STAR SAPPHIRE, Untreated

The rays of the star are said to represent Faith, Hope, and Destiny.
People thought the ages have adored its unique and serene nature.
It has been said that the three interesting rays of light in a star sapphire represent Faith, Hope, and Destiny.

The overall appearance of the star sapphire in the photograph on the next page is well executed. The star is fairly visible even under normal lighting, and when a penlight is shined on it, six sharp and distinct rays of light appear across the whole surface of the stone. The star moves to the right when the stone is tilted to the right, and to the left when the stone is rocked toward the left. As in star rubies, the rays of the star appear weaker in more transparent stones.

" Star sapphire" refers to cabochon-cut blue or gray corundum that exhibits the star effect, or asterism. Star may appear in other members of the corundum family such as ruby and violet sapphire, but orange and yellow sapphire do not exhibit stars.

Ninety percent of all star sapphires are mined in Sri Lanka, and they have been loved over the ages for their uniqueness and their serene appearance. Many of the blue sapphires mined in Sri Lanka, both the cabochon-cut ones showing the star effect and those that are faceted, are natural-colored stones that do not undergo heat treatment. Heat applied to such sapphires during ring resizing may alter their color, making them lighter, so jewelers will exercise special care with these. It is thought that natural gemstones maintain a never-changing color; though this is usually the case, there are instances where they can easily be altered by heat.

There is also the near-colorless sapphire rough called "geuda" which contains silk inclusions and will become a gray star sapphire when cut into a cabochon. Heating this rough material at high temperatures causes the silk areas to turn the stone blue, and sapphires treated in this way are very popular. Therefore, rough crystals of this type that have few imperfections will be heat-treated and made into faceted sapphires instead of being cut as cabochons that show the star effect. Geuda, with its high likelihood of becoming a beautiful sapphire, commands a high price.

Name of mineral : Corundum
Mohs hardness : 9 
Refractive index : 1.762 ~ 1.770 
Specific gravity : 4.00

SYNTHETIC STAR CORUNDUM

It is amazing how people can have such admiration for gemstones created by nature, while at the same time seeking to gain a profit by imitating them.

Synthetic ruby was first commercially manufactured in 1904. When considering how humans can make synthetic materials that are structurally identical to gemstones--- even making them exhibit a star--- one cannot help but appreciate the power of technology. It is even possible to control such aspects as the appearance of the star, as well as the appearance, coloration, and tone level of the material.

However, since the production of synthetic stones can be increased simply by expanding facilities, their supply is virtually infinite, and they possess no rarity. Though they may be used as components for accessories, synthetic stones are not gemstones. There is almost no current demand for these synthetic star sapphires and synthetic star rubies.

There are also stones being treated by scientifically diffusing color- or star-causing agents into the surface of natural colorless corundum to produce a blue color or a star (a process known as surface diffusion treatment). It appears that such diffusion-treatment blue sapphires have been sold in the Thai gemstone-cutting center of Chanthaburi in recent years. There are totally different from the above-mentioned synthetic star sapphires, but since their prices are cheap, measures must be taken so that they do not end up being mixed in with natural material.

A professional jeweler can positively distinguish between natural and synthetic star corundum. Modern gem identification and separation techniques a re advancing in leaps and bounds. A specialist can separate natural and synthetic by such means as optical and compositional analysis, as well as by looking for evidence of natural crystal growth.

Synthetic Star Sapphire

Size (mm): L 9.0 x W 6.8 x D 3.32

Synthetic Star Ruby (Translucent)

Size (mm): L 9.0 x W 6.9 x D 3.50

Synthetic Star Ruby (Opaque)

Size (mm): L 8.9 x W 7.0 x D 3.56

JUDGING QUALITY

Just as with star ruby, star sapphire's quality is judged based on beauty and tone of color, and the pivotal quality factor is whether the blue color is distinct or not.

As far as the star's orientation goes, cutters believe that if all other factors are equal, it is better to have the star centered along the vertical axis (as in the gemstone shown on the quality scale in 5-S) rather than along the horizontal axis (as in 2-S). A vertically centered star will make the stone look larger and more beautiful, increasing its value.

 

QUALITY SCALE
STAR SAPPHIRES 
Untreated

HOW TO CHOOSE

A faceted gemstone will exhibit brilliance regardless of its color, allowing enjoyment of the beauty of its mosaic pattern. However, a cabochon-cut gemstone with a gray color will not across as beautiful. There may be people who would be satisfied just enjoying the appearance of a star, but such a stone has no true value as jewelry. The first recommendation is to select a blue stone, even if it is small.

Second, choose a stone that at least shows signs of the star under normal lighting, while showing distinct, sharp, and straight bands of light when lit with a penlight.

With loose stones, avoid cabochons that are too high or too low, and take care to select one with a base that is not too deep.

The value of a three-carat-size, untreated star sapphire of jewelry quality is approximately US $3,000 for the stone alone. (2001)

A GEM OF VALUE

VALUE INDEX

ct size	GQ	JQ	AAQ
10	12.0	5.0	0.7
3	3.0	1.0	0.1
1	0.3	0.15	0.04

	-GQ-Gem Quality
	-JQ-Jewelry Quality
	-AQ-Accessory Quality