Sapphire

Sapphire September's Birthstone
Colours Various
Family Corundum. Al203
Hardness 9
Refractive Index 1.76 – 1.78
Specific Gravity 3.97 – 4.05
Crystal System Cubic
Enhancements May be Enhanced
Major Sources Namibia, Nigeria, Sri Lanka, Mali, India Kenya, Zambia, Mozambique, Tanzania, Russia, Madagascar
Warnings for Care Colour change occurs at moderate to high heat

Sapphire Facts

The name Sapphire come from the Greek word for blue, although in the middle ages the name was applied more to what we know today as Lapis Lazuli. Sapphire and Ruby are members of the  Corundum family. If Corundum exhibits a colour from slightly pinkish red, through red to slightly reddy brown then it is called a Ruby. All other colours of Corundum are termed Sapphires. So while we traditionally think of Sapphires as being only blue stones, they actually come in all colours from black to white.  Corundum is second only to Diamond in terms of its physical hardness, (although exhibiting only  1/140th of the hardness of Diamond), This hardness (9 on the Moh's scale) in relation to all other gemstones has ensured Sapphires position with Ruby and Emerald  as one of the so called "precious gems".

Sapphire is the birthstone for those whose birthday falls in September, and for those born under the star sign of the Taurus.

Topics Of Interest:
Sapphire - What Causes the Colour
Purchasing Sapphire
Mineable Deposits
Sapphire - Common Treatments
Important & Famous Sapphire
Sapphire - The Legend

Sapphire - What Causes The Colour

In Blue Sapphire the causal agent is trace amounts of Iron or Titanium, a  violet hue being caused by the presence of Vanadium. When the trace content of Iron is very low, yellow and green tones are produced. While the inclusion of Chromium in the lattice produces a pink colour in the stones. Blue is however the most famous and desired of the sapphire colors. The prized Kashmir and Burmese Sapphires have a deep intense almost velvety blue colour, and represent the pinnacle of colour perfection

Padparadscha from the Singhalese word for  lotus flower, is a very rare sapphire which exhibits two colors simultaneously, pink and orange, and like Ruby and unlike all the other fancy coloured Sapphires has its own name. This being due to its rarity and value.

Purple is another rarer colour for Sapphire, being  found in Sri Lanka and Tanzania. In these deposits Iron and Titanium which normally produce the common blue colour, has under specific concentrations and conditions caused the purple hue of the stone.

Colorless or white Sapphires are rare as faint shades of color (typically blue and pink) are nearly always present.

Many of the fancy coloured Sapphires are under microscopic examination merely combinations of banding in two distinct colours. Green for example is actually the result of closely space blue and yellow colour band within the stone.

Purchasing Sapphire

Color
All Corundum’s (Ruby and Sapphire)  are graded on  the purity of their primary hue or colour. For blue Sapphires, the primary hue is blue, while violet, purple and green are the normal secondary hues. Violet and purple can contribute to the overall beauty of the color, while a green overtone is considered a negative trait and it to be avoided. Blue sapphires with typically a primary Blue hue comprising 85% of the colour and secondary (violet or purple) hues contributing 15% to the colour are said to be of fine quality. Blue sapphires with any amount of green, a distinct negative, as a secondary hue are less attractive and  not considered to be fine quality. A Gray tone is a normal and common saturation modifier or colour mask in blue sapphires, this effectively reduces the saturation or brightness of the hue and therefore has a distinctly negative effect on the stones appearance and value

Lighting
Sapphires are a daylight stone looking their best when expose to natural sunlight. After dark or indoors, they still look very attractive under fluorescent light. Incandescent (tungsten) light  which is a soft light found in all but the latest energy saving globes is a redder, warmer light, which does no real justice to the gem, making them appear dark and dull compared to their appearance in daylight.

Clarity
Second to colour, clarity is the next most important criterion to consider when purchasing a sapphire. Good quality stones should be clear of visible inclusions to the naked eye or eye clean. Sapphire tends to be cleaner than ruby and larger unincluded pieces are not uncommon. Under microscopic examination almost all sapphire are actually included. The presence of a find rain of inclusions or fine needles within the stone can impact significantly on the appearance of the stone in a distinctively positive way. The famed Kashmir Sapphires has a rich almost velvety appearance due in part to the presence of fine inclusions, not visible to the naked eye. Star Sapphire (Asterism)  is common in those stones with a high content of fibrous or needle like inclusions, typically needles of Rutile. The star manifests itself as a 6 rayed or pointed star when view from above in a en cabochon cut.

Cut
No one cut particular  favours the natural beauty of Sapphires. As such all cutting styles are commonly produced, with rounds dominating the smaller sizes and ovals and oval or square cushions in the larger sizes. Lower grade slightly less transparent rough is often cut  en cabochon or as round brilliants where the added brilliance the cut imparts to the stones  can help to mask their lower quality. Those stones with a high Rutile needle content are cut en cabochon with care being taken to ensure the orientation of the needles in the finish piece creates a centered, symmetrical and clear star effect.

Mineable Deposits

Sapphires are abundant in many localities around the world, although some of the once prolific producing areas are now heavily depleted, or completely worked out. Historically the mines of the Kashmir region of India and Mogok valley in Myanmar (Burma) have produced some of the finest material known, but today production is limited and care should be taken when purchasing stones at a premium based on their provenance. Significant deposit are located across South East Asia, (Thailand, Vietnam, Cambodia and South East China). In addition Sapphires occur in Africa (Tanzania, Kenya, Nigeria and Madagascar), Australia and Sri Lanka.

In the 1980's about 70% of the world Sapphire production was coming from the Australia, although the quality was of a commercial nature, rather than top gem quality. In recent decades this dominance has declined. Today Sri Lanka and Madagascar produce most of the fine sapphires finding their ways on to the worlds rough markets

Sapphire - Common Treatments

Heat Treatment
Sapphire like their cousins Rubies are commonly heat treated to enhance their colour and to even out or totally remove "silk". While initially only stones of a lower quality were treated in this way, estimates coming for South East Asia indicate that heating is now carried out of about 95% of all rough material, as part  of an industry accepted enhancement technique. Heat treatment is used specifically to improve and even out the colour in Sapphires, and when done at a moderate heat will reduce the presence of needles. At higher temperatures needles, specifically of Rutile are completely removed by a process of melting and re absorption. These heat treatments enhancements  typically occur around temperatures of 500  - 1800 °C, in computer controlled electric furnaces. Some cutting houses still use the older process of low tube heat, when the stones are heated over charcoal at a temperature of about 1300 °C  for 20 to 30 minutes, a process know in the trade as "Chanthaburi cooking". The silk is only partially broken as the color is improved, imbibing the stone with a richer luster, and better colour.

Diffusion Treatment
The diffusion technique is essentially a method of coating a natural Sapphire with a "skin" of colour. The compound for diffusion is effectively bonded into the outer layer of the cut stones as they approach their melting point, thus forming a composite lay of essentially Sapphire and the diffusion agent on the stones surface. The depth of this colour enhanced skin can vary  from a few microns to an millimeter or more depending on the method used. Initially this was confined to blue Sapphires of a lower blue or  green colour, and the diffusion coating was Titanium oxide, which imparted a deep blue colour to the stones. Recently Beryllium is being diffused into the surface of  fancy yellow and pink sapphires at very high heat, and again close to their melting point.  This process  produces stunning red and orange colours that are only rare and expensive in nature (Padparadscha).

Important & Famous Sapphire

 

Very large sapphires are as a rule rare and as such are sometimes named in the same way as diamonds. One of the largest facetted blue Sapphires is the 423 cts Logan Sapphire currently on display at the Smithsonian Museum of Natural History in Washington. Other famous ones are the Midnight Star, the Star of Asia,  and the Star of India. In the case of the latter at 536cts this is the largest cut Star Sapphire known, and currently resides  in the American Museum of Natural History in New York.

The British Crown Jewels hold two exceptions blue Sapphires, the St Edward's and the Stuart replicas of which are on display at the Tower of London

Sapphire - The Legend

Sapphire is the birthstone for those who are born in the month of  September, and for those born under the star sign of  Taurus.

Through history, Sapphire has symbolizes truth, sincerity, and faithfulness in relationships, bringing peace, joy and wisdom to the wearer and owner. In the past, Sapphires was also believed to be a talisman that would protect against evil spirits.

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