The sapphire stone was known to the ancient Egyptians as ‘the stone of the stars’. They believed that sapphire stimulated honesty, truth and justice.
Whatever its properties and “powers”, the colour and purity of this stone, as coveted and prized as the diamond, arouse the desire and interest of jewellery lovers.
The name sapphire is derived from the Greek word sappheiros, meaning “the most beautiful”, and the Latin word saphirus, meaning “blue”.
It was widely used by kings, queens and great men of the Church.
Set in rings, diadems and crowns, they represented the high social status of the people who owned them.
Even today, the English court displays its exceptional pieces set with this precious stone.
Sapphire belongs to the group of corundum minerals with gemological qualities.
Sapphire is basically composed of aluminium oxide with the chemical formula Al²O³. In its natural state, this chemical compound is colourless.
In the case of sapphire, the characteristic blue colour is due to the presence of titanium and iron in its composition.
Although the name sapphire is related to this colour, the gemstone as we know it has a wide variety of colours due to the presence of “metallic impurities” in its composition.
Sapphire can be mistaken for other stones. Some of the pieces used in ancient times were set with gems such as lapis lazuli or topaz, which were believed to be sapphires. It wasn’t until around 1800 that sapphire was discovered to belong to the corundum group.
Corundum is an aluminium oxide mineral known for its hardness (9 on the Mohs scale) and intense lustre. Because of these characteristics, it is widely used as a gemstone in its different varieties. The main ones are sapphire (blue) and ruby (red).
Depending on the presence of certain elements, sapphires can be found in different colours, such as
- yellow (low iron content)
- green (due to the presence of titanium)
- Pink, purple, brown, orange (due to the presence of iron and chromium)
- Padparadscha sapphire, orange tending towards salmon pink (due to the presence of iron and chromium)
The name sapphire (without adjective) always refers to blue.
In the case of sapphires of other colours, the name always takes the colour as a complement; they are also known as fancy.
Red corundum always refers to ruby.
Sapphire (blue) is widely used in jewellery for engagement rings and distinctive designer pieces, mainly because of its intense, vibrant colour.
In recent years, however, coloured sapphires, especially yellow sapphires, have become increasingly popular. The possibility of replacing the rare and expensive diamond has been embraced by countless celebrities.
And, of course, it has become a popular item.
Sapphire’s gemological characteristics
Sapphires have a high degree of hardness, which increases their value and the difficulty of cutting them.
- Hardness – 9 Mohs
- Relative density – 4.0
- Fracture – conchoidal
- Translucency – can vary from transparent to opaque and has a vitreous to translucent sub-adamantine lustre.
Sapphire has a pyramidal habit, crystallising in hexagonal bipyramids with transverse striations on their faces.
Its main composition is aluminium oxide, with traces of other elements such as cobalt, iron, titanium and chromium, which give the gemstone its colours. In addition to the colours already mentioned, they can also be found in grey and black.
The best sapphires come from Kashmir in India, but these mines are sold out. That’s where the sought-after blue sapphires come from.
In Thailand, in Chanthaburi, sapphires range in colour from dark blue to aqua green.
Australian sapphires are not of the highest quality; they are watery blue and sometimes black.
In Sri Lanka (Ratnapura region) there is a light blue stone with a hint of purple. There are also coloured sairas and the Padparadscha saira, which is orange and tends towards salmon pink.
The finest stones command high prices and are found in Sri Lanka, Vietnam and Tanzania.
The main producing countries are Burma, Thailand, Sri Lanka, Australia and Madagascar.
It is rare in Brazil, being found in Mato Grosso, Goiás, Santa Catarina and Minas Gerais.
The largest centre for cutting sapphires is India.
Sapphire colour
1. White sapphire or leucosaira
White sapphires are actually colourless. There are no elements present that could change their colour. They are now widely used in jewellery as an excellent substitute for diamonds in engagement rings.
They only lose in brilliance. They are cheaper than the yellow, pink and blue and are very durable. Although they are rare, they are not as much in demand, which makes them more affordable.
2. Yellow Sapphire
White sapphires are actually colourless. There are no elements present that could change their colour. They are now widely used in jewellery as an excellent replacement for diamonds in engagement rings.
They only lose in brilliance. They are cheaper than the yellow, pink and blue and are very durable. Although they are rare, they are not in such high demand, which makes them more affordable.
Yellow sapphires are becoming increasingly popular and sought after. Like white sapphires, they are a great alternative to diamonds. However, their special colour adds a cheerful and youthful touch.
The colour is due to a low iron content in the corundum.
Some say that this gemstone stimulates creative energy and brings prosperity. It activates the intellect and action.
3. Pink Sapphire
The colour of this sapphire is due to the low amount of chromium. If the amount is high, the colour would be red and then a ruby. This line, which separates a pink skirt from a ruby, is always confirmed by gemmological tests and an analysis of the amount of chromium present.
The pink colour is also in great demand on the market. They were recently found, about 15 years ago, on the island of Madagascar, where they are becoming increasingly common.
Before that they were only found in Burma and Sri Lanka.
They range from light, intense pink to bubblegum pink. The latter is very popular in jewellery.
4. Violet or purple sapphire
The colours violet and purple are often confused, but they are actually different shades of the same colour.
Purple is a mixture of red and blue, and violet is purple and white. These colours are rare. They are often mistaken for amethyst.
Violet sapphires have a unique characteristic in that they can change colour under different types of light.
5. Grey and Black Sapphire
Black sapphire is mined in large quantities and is almost opaque. They are cheap and considered to be of low quality.
They can replace onyx perfectly. Sometimes they can be very dark grey.
6. Orange Sapphire
Orange sapphires are also rare, but because their colour isn’t the most popular, their price hasn’t kept pace. The orange colour, which is a mixture of chromium and iron, isn’t the most beautiful or pleasant to look at either.
7. Green Sapphire
Green sapphires are rare. It can be found when blue and yellow sapphires are found in the same mine. There is little demand for this colour, so prices are not high, as emeralds and tourmalines are easier to find.
Green sapphires are darker or very light in colour, but have an intense lustre. Traces of yellow and blue can often be seen under magnification and sometimes even with the naked eye.
8. Padparadscha Sapphire
Little known to the general public, Padparadscha sapphires are highly prized by gemologists, collectors and experts in the field. The name comes from the Sangali word meaning ‘lotus colour’.
Its characteristic colour is defined as an orange pink tending towards salmon. Although renowned laboratories such as AGTA and GIA differ on the certification of these sapphires, most have this colour and come from Sri Lanka and, controversially, Madagascar.
They are very rare and expensive, the “darling” of sapphires.
9. Sapphire
Sapphire is the most precious and valuable of all blue gemstones. It is distinguished by its incomparable colour and brilliance.
When we say “sapphire” we are always referring to the blue colour. One of the most famous is the ‘Logan Sapphire’, which is deep blue in colour and exceptionally clear, especially for a stone of its size. It was tested by the Gemological Institute of America in 1997 and found to be a naturally coloured sapphire with no evidence of heat treatment.
Recently, the world’s largest sapphire, weighing 42kg, was found in Sri Lanka.
Guruge Gems, the company that owns the stone, split it into several pieces and cut out the gem you see in the picture, which is worth an incredible $800 million.
This colour has always been a favourite of churchmen, kings and queens, as it carries spiritual significance and prosperity.
What is asterism?
In gemology, asterism is the property of some minerals (e.g. sapphire, emerald, garnet) to show the image of a star due to the reflection or refraction of light caused by inclusions of the mineral rutile.
When the presence of this mineral is small, it gives a silky appearance; when it is larger, it causes asterism.
There are some scholars who argue that rutile does not cause asterism, but rather the presence of crossed hollow channels in three directions.
Sapphires with this effect are called star or asterism sapphires and their value depends not only on the carat of the stone but also on its colour and the visibility and intensity of the asterism.
Recently, this phenomenon has been created in synthetic sapphires, which has considerably reduced the value of natural stones that display it.
For the star effect to be perfect, the gemstone must be cut in the shape of a cabochon or sphere. In some cases, the star will appear to move as you turn the gemstone.
Stars can have 4, 6 or 12 points.
Synthetic Sapphire
Synthetic sapphires, like other gemstones, are not artificial.
This confusion can be caused by inexperience or mistranslation. Synthetic gemstones have no trace or origin of the natural gemstone, i.e. they don’t exist in nature.
Synthetic gemstones, which are produced in laboratories, have as their raw material powdered natural gemstones, which undergo a process of melting and recrystallisation so that their properties are very similar to those of the natural gemstones, and in some cases identical.
This synthesis can only be identified using a gemological microscope. Because they undergo rigorous and expensive processes, synthetic gemstones have a high value, but are more affordable than natural gemstones.
The most widely used methods for synthesising synthetic sapphires are:
- The first method is the flame fusion or Verneuil process, developed in 1902 by the Frenchman Auguste Verneuil, which is still the most widely used and one of the cheapest.
In this process, aluminium oxide powder is placed in an apparatus and then oxygen is injected, forcing the mixture downwards to meet the hydrogen injected at the bottom of the apparatus.
This causes combustion with a flame that reaches 2000°C. The aluminium oxide powder melts into drops which fall onto a support, cool and crystallise to form corundum.
The addition of salts of chromium, titanium, iron, etc. to this process produces sapphires, coloured sapphires and rubies.
- The luxury process is based on dissolving the aluminium oxide (in the case of sapphires and rubies) in a molten compound that acts as a solvent. This mixture is poured into a platinum crucible and then placed in a furnace at a temperature close to 1,300ºC.
- The hydrothermal process involves various techniques for crystallising substances in aqueous solutions at high temperatures and vapour pressures.
- Other processes such as Czochralski and float zone are also used.
Many synthetic sapphires are produced for industrial, commercial and technological applications.
In order to determine the natural or synthetic origin of a gemstone, it is essential to examine the inclusions under a magnifying glass and microscope. Some other characteristics, such as the nature and content of its trace elements, can give an indication of this origin, but they are not diagnostic.
Natural sapphires usually have mineral and fluid inclusions as well as linear colour zoning.
Sapphire Treatments
1. heat treatment
Heat treatment is used to enhance or even change the natural colour of the gemstone. Sapphires can be made lighter or darker.
It is also used to improve the clarity of the stone. High temperatures of 1,500 to 1,800ºC are used, in electric kilns with or without oxygen.
The final colour is permanent and very stable as long as the stone is not exposed to high temperatures again.
This treatment is considered the most natural and acceptable by the GIA and other certifying laboratories as no components are added.
This process “finishes” the chemical reaction of the mineral impurities that occur naturally in the stone.
2. Diffusion
This process consists of introducing impurities into the gemstone by diffusing oxides at high temperatures (around 1,900ºC).
The gemstone is placed in a crucible, mixed with titanium oxide or another powdered colourant and heated to a high temperature. The atmosphere and time are variable.
The result is a thin, highly coloured layer of stable colour.
3. Whitening
Whitening involves the use of chemical products to lighten the yolk or remove unwanted colours.
Other treatments such as cavity filling, heating followed by cooling and tinting are also used, but many are temporary and unacceptable.
Sapphire grading
As with other coloured gemstones, sapphires are graded on the basis of colour saturation and intensity, clarity, cut and size – the same 4Cs as diamonds.
1. COLOUR
Sairas come in a wide range of colours and each colour has its own quality variations. In general, the more intense the colour and the fewer the inclusions, the more valuable the gem.
For blue sapphires, the assessment of colour is more important in determining value.
The most prized are velvety blues to violet blues (called violet-blue) among medium dark hues. The saturation should be as strong as possible without darkening the colour and compromising brilliance.
The colour grading of sapphires is divided into three quantifiable categories: intensity (saturation), hue (colour) and tone (light/dark), as defined by the GIA.
Terms such as “blue”, “slightly greenish blue”, “very slightly greenish blue” are used to describe colour trends.
The colour gradation nomenclature also specifies six levels of saturation, from “greyish” to “moderately strong” to “vivid colours”, and nine levels of hue, from “very very light” to “very very dark”.
2. TRANSPARENCY / CLARITY
The degree of visibility through a sapphire is known as its clarity, which varies from transparent to opaque, with transparent being the ideal, as categorised below:
Transparent
Clear and distinct visualisation of objects through the stone. These sapphires generally have excellent brilliance despite any inclusions.
Semi-transparent
Slightly blurred visualisation through the stone.
Translucent
Sapphire is difficult to see through. Light is slightly diffused.
Semi-translucent or semi-opaque
A small amount of light passes through the stone.
Opaque
Very little light passes through the stone.
Blue sapphires tend to have more inclusions than most coloured sapphires. The term “inclusion” is used to define features found within a gem and is often used to indicate that the stone is of natural origin.
Inclusions generally reduce the value of a gem, especially if they threaten its durability. They can take various forms, such as crystals (solid inclusions like small grains), silk (fine rutile fibres), which, although an imperfection, is preferred because it sometimes gives the gem a velvety appearance, increasing its value, cracks, fingerprints (inclusions that have the appearance).
3. CARAT / WEIGHT
The effect of carat on the value of a sapphire varies with colour. Yellow sapphires are relatively common in sizes over five carats, but five-carat Padparadscha sapphires are extremely difficult to find.
Blue, pink, orange or Padparadscha sapphires over fifteen carats are particularly valuable.
Because sapphires have a high density, a one-carat sapphire looks smaller than a diamond of the same weight.
4. CUT
Comparable to diamonds, the best sapphire cuts offer a greater depth/width ratio.
Deeper sapphires appear smaller but show more colour than when cut to normal proportions.
They also preserve the weight and therefore the value of the gem. When cut shallowly, they appear lighter in colour than when cut deeper. Quality sapphires have good symmetry when viewed from a distance – they reflect light evenly.
As the original shape of the crystal is a hexagonal pyramid, deep cuts provide better colour and proportions.
The cuts are based on colour zoning (different colours in certain areas), pleochroism (different colours in different directions) and the clarity of the gem.
The star sapphire is always cabochon cut to show off the star.
Most sapphires are cut in oval, emerald, round and cushion cuts. In mixed cuts, the pavilion is cut in parallel steps and the upper part is of the brilliant type, as in the emerald cut, which allows the gem to be better utilised.
At present, in Thailand, India or Sri Lanka, the vast majority of sairas have mixed cuts.
In the picture below you can see the most common types of sapphire cuts.
Sapphire Care
Because of its hardness, sapphire doesn’t need much care and can be cleaned with warm water and soap, or with one part ammonia to six parts water.
Use a toothbrush to scrub behind the stone where dust can collect. As with most gemstones, avoid heavy work or contact with chemicals as this can damage the stone.
