Star Sapphire Gemstones - Variety of sapphire
The star sapphire gemstone is a variety of sapphire which has been found to have a characteristic only known as asterism; this is when the sapphire seems to produce a star of light that comes from the center of the stone
If a skilled cutter takes a good look at the rough, he should be able to tell whether this will produce a start sapphire or not. This cannot be seen through the naked eye until it is cut. Then position of the star effect, with respect to the positioning of the center of the gemstone will determine the value of the stone after cutting. The depth and clarity of the gemstone will also affect this effect and also affects the price. The stars which seem to appear closer to the top of the gemstone will have four points, but it is very rare that you come across one that has six points, and this is considered a truly valuable specimen.
Most start sapphire are cut in cabochon forms, and they have a dome that allows the asterism to be seen clearly. This effect would be lost if the stone was cut in any other fashion.
The light that comes out of the star sapphire is caused by needlelike inclusions, which make the light to bounce around within the crystal and come out in the form of a star. The light will hit these inclusions, which are arranged parallel to one another and will force the light to be concentrated in points which form the star. When there are two or more of the bands intersecting, then the star pattern is formed. This is a very difficult effect to describe and it has to be seen in order to be believed. Usually, depending on the crystal, the star will have six to twelve rays of light.
The star sapphire comes in various colors. The main ones are blue, black, brown, Purple, Green, Plum and rarely in orange. If the gemstone is found in any other color apart from blue, then this color must be added to the name e.g. Orange Star Sapphire. There are times when you find this gemstone in the yellow colors. The star sapphire is a corundum by family.
The key separations of the star sapphire are appearance, the refractive index and through magnification. The black star sapphire is a name that is used to cover the dark varieties of all the colors. This is a gemstone with a transparency of semitransparent to opaque, and has a refractive index of about 1.762 to 1.77. It has a birefringence of about 0.008 to 0.01 and has a uniaxial optical character; it also has a negative optic sign. When viewed under the polariscope, this gemstone is doubly refractive. The fluorescence of the stone, when viewed under long and short wave ultraviolet light is light blue weak tones which are moderate to strong red. The dark tones are inert. The stone has no pleochroism, though some of them have a weak one. The same stones may look like the non-asterism counterparts and the pleochroism will depend on the transparency of the stone. It has a weak dispersion with a fire value of 0.018.
This is a corundum and is made of aluminum oxide. It has a hardness of 9 on the Mohs scale, making it a very hard stone, and it has a white streak. It has a specific gravity of 3.95 to 4.1 but typically of 4.0. It has excellent toughness and a high number of inclusions. The inclusions will seem silky and are sometimes seen as parallel rutile needles, which will then produce a six ray star. There are hexagonal growth lines and some color zoning mineral inclusions are also seen at times. There star characteristics are affected by the strength of the body color. A weak body color has a weaker star effect. When in the natural state, the star will have one of the rays running perpendicular to the growth zones which run hexagonally. It is very rare that you come across a stone that will have the full set of 12 rays, but this is a phenomenon that is seen in the black and dark stones. This is a gemstone that has a sub adamantine to vitreous luster and is very stable. It has a conchoidal fracture and has no cleavage.
However, the twinned stones may show some parting.
A profile of the star sapphire gemstones
They say that any corundum that has rutile inclusion is blessed because it will display the star effect. Not only will the gemstone have a great star, especially when talking about the blue sapphire, but the rutile inclusions will also interact with the iron to bring a deeper blue color to the stone. However, there is also a downside to all this.
You see, Rutile, is actually titanium oxide and it cannot do both these feats at the same time. The rutile must be chemically in different states in order to produce the blue color and also produce the star. When the rutile is left in an undissolved state, it usually collects into deep dark bundles, of tiny minuscule needles, and when found in abundance, then the corundum will have a clarity that ranges from translucent to opaque. The corundum stones which have a high level of rutile in the crystals usually seem to have a milky feature which is refered to as silk in the gemstone world. The stones which have moderate levels of partially dissolved rutile will have a grayish to light and blue colors, and these are usually cut into cabochons. When these stones are cut into cabochons, the inclusions then produce a star effect which is known as asterism; the star has six sides since the crystal of the corundum also has six sides.
Many of the rutile-rich gemstones always ended up in these cabochon shapes for several centuries. However 25 years ago, one of the dealers in Bangkok found that it was possible to dissolve this rutile in ovens. In the altered stare, the rutile in the stones cleared up and the cloudy gemstones soon took a permanent blue color.
Once the Bangkok dealers discovered this alchemical feat, they rushed into Sri Lanka, where they were able to buy the rutile-rich, silk varieties of the corundum, at pennies per carat, since they bought it in huge quantities. They then took these to their oven and turned them into beautiful gemstones. It was not long before the people in Sri Lanka found out what was going on, and the price of these gemstones went up incredibly. It was not long before the mountains where this rough came from, were turned into molehills as people mined the corundum. It was not long before the Thais too started baking their own stones and even heating some which had already been turned into cabochons, hoping that they could get them to become clear too and increase their value. Soon they were hunting for start sapphires that could be turned using the same baking and increasing their market value.
As a result of this. The existence of the star sapphire is dire need as most people want them to be taken to Bangkok and be baked into the clear sapphires. The existing and potential stock seems to be destined for this treatment. The gem species has also been endangered by the fact that the United States of America has also found a way in which they can make synthetic star sapphires.
The Linde Stars
Nature may be very good at making wonderful star sapphires but man has surpassed her in this respect. When union carbide became the first company to produce the first synthetic sapphires, they were immediately named, The Linde Stars. This occurred in the late 1940s and these manmade stars produced rays of light that were so sharp and straight that they made the natural ones seem like crooked and low quality varieties. For most traditionalists, the Linde Stars offended them then and still do to this day. However, for most consumers, they decided to adopt the straight stars; this has been the trend to the effect that they are preferring to have the natural ones, which have the straight lines that are produced by the synthetic ones, even if they have to pay a lot more for them. The asking that natural start sapphires have the straight points of the synthetic ones is not fair at all, especially when you consider that most want those with the lovely blue color that connoisseurs have come to love so much.
As mentioned earlier, it is when the light is reflected from the rutile needles that you finally get the asterism that is so dearly loved in these gemstones. The corundum that has this effect is mainly mined in Sri Lanka. These varieties have a denser packing of the needles, and when they are more pronounced, then the better quality of star the stone has.
Union Carbide is the one company that mainly deals with synthetic star sapphires and these are made it its subsidiary, the Nakazumi Earth Crystals facility in Japan. They are able to put in so many tiny needles of rutile into a stone that the star produced is so precise that it seems to have been painted into the stone. The Chief gemmologist at the Gemological Institute of America, John Koivula says that the painted look of the star which seems to sit in the stone and not come out of it is one way in which specialists are able to tell the synthetic variety from the natural one.
However, the fact that the stars lack depth and seem to look like decals placed in the stone has not dampened the need for the synthetic variety, something which the crystal growers are very proud of. While looking at the stones that have this feature, many dealers will tend to seem apologetic for the stubby rays and uneven nature of the rays that come from the natural variety of the star sapphire. This is especially pronounced in those which have a deep blue color.
The jinx of fine stone cutting
There is no need to make apologies for the natural stones; you see, the star sapphire is classified as a phenomenon stone, and the quality of the star should mean more to the buyer than the color of the gemstone. Therefore, it comes as no surprise that you will find dealers who say that they tend to sell just as many fine gray sapphires as they do fine blue specimens, simply because the buyer was more enchanted by the quality of the star. The gray stones seem to have better stars than those of the blue. Each of the stars seem to be running all the way to the bottom of the cabochon.
Gray stones however do not just rely on the star as their selling feature, they are also superior in their makeup. The blue stones are more translucent than the gray ones, and the cutters have to preserve most of the rough, and also the rutile in it, in order to have a great combination of color and asterism. This means that the blue stars have to be cut with the bottom parts sagging down, while the gray ones are cut with a flat base. Therefore, for most jewelers and consumers who do not know why the blue star sapphire must be cut in this way feel that this is an unnecessary addition of weight and cost, so they opt for the gray ones.
The fact that the Lindes have very slim lines and also have very great stars will make many dealers have a hard time explaining to a customer why the blue must have a bulging belly. The bottom bulk of the gemstone can easily be hidden in the fitting of the jewelry, but most buyers see this as an ugly feature. It is only the fact that you can only rarely find a deep blue star that has a perfect blue color, which will make the buyer not feel uneasy in having to pay extra for the bulge.
Even if there are a few missing sections about this fine gemstone, the fine blue sapphire will get a high value, per carat, an only one in ten of those top colors will have good and well centered stars. Who can blame them? This is the reason why some people will pay extra in order to have the plain and powdery fine blue sapphire as opposed to the star sapphire.
This is a gemstone that will appeal to people who want to stand out from the rest. When people are flaunting their powder blue sapphires, the unique fashion fan will want to stand apart and go for the star sapphire even if it might be considered to be lesser than the former. This is a gemstone that has had a very difficult history bit it is still holding its own in the finicky gemstone trade. Given this long hold, despite the turbulence and challenges that it has faced, this is a gemstone that will one day become very valuable, as people start looking for the natural ones, most of which are being baked into clear gems, and it will be rare to find a star sapphire that is natural anymore.