Apsara Gems - Gem Treatments

What are gem treatments?

Many different types of gemstones have been treated in one way or another for hundreds of years. There are records of heat-treatments being applied to rubies & sapphires, which date back to the 11th Century. The types of gem treatments used today vary a lot but they all have the same goal - to improve the colour and / or the clarity of the gem.

Gem treatments include anything from heating, irradiation & oiling to name a few. Some treatments like the high temperature heating applied to rubies and sapphires, are permanent and irreversible. Other treatments such as the oiling of emeralds are not permanent and may need re-treating from time to time.

Diamonds can also be subjected to various treatments. These include irradiation to produce coloured diamonds, laser drilling / bleaching to remove dark inclusions and fracture filling to improve clarity. More recently high-pressure high-temperature treatment (HPHT) has emerged as one of the most controversial, as it can greatly improve a diamond’s colour but is difficult to detect. Coated diamonds can also be a problem. These stones are coated with a thin layer of colour to make them resemble coloured diamonds. The coating is not permanent and is usually performed for the purpose of deception.

A crucible containing heat-treated sapphires ...

A crucible containing heated blue sapphires.

There are many different types of gems, which are heat-treated as a matter of routine. Some gem types would not exist in their present form without heat-treatment. An example of this is tanzanite, which owes its purple / blue colour to heat–treatment. Many other gems are routinely heated including rubies, sapphires, aquamarine, tourmaline, topaz, zircon and amethyst along with many others.

The Heat-Treatment of Rubies & Sapphires

Removing blue sapphire crystals from the clay ball after old-style treatment.

The heat treatment of rubies and sapphires has been performed for hundreds of years but it is more recent years that ruby & sapphire heat-treatments have been performed as a matter of routine. During the 1970’s & 80’s heat-treating technology evolved dramatically and heat-treated Sri Lankan geuda sapphires began to pour onto the market. Rubies from Bo Rai in Thailand and Pailin in Cambodia also responded well to heat-treatment by removing the brown or purplish overtones and lightening the colour. During this time the treatment process was a bit of a hit-and-miss affair. The sapphire & ruby crystals were enclosed in clay balls with a few secret ingredients and potions, then placed amongst smouldering charcoal and left for hours or even days to ‘cook’. In more recent years furnaces powered by gas, diesel or electricity have replaced the smouldering charcoal fires. Modern ovens have much more control over the cooking process and give much better results than the earlier methods.

The Heat-Treatment Process

The stones are placed in a crucible and heated in a furnace to enhance colour and/or clarity. Depending on the type of gem being treated, the furnaces can be powered by gas, electricity, diesel or charcoal. During the treatment process, inclusions with a lower melting point than the corundum host, dissolve. The stones are 'soaked' at high temperatures then slowly cooled. During the cooling process the inclusions and impurities re-distribute themselves in the crystal lattice. The re-distribution of these inclusions can have an effect on colour and clarity.

Gas-combustion furnace

Gas-combustion furnace used for heating blue sapphires.

Crucibles used as a container for the sapphires during heat-treatment.

An example of this is the dissolving of rutile silk inclusions in blue sapphires which both improves clarity and colour. This heat treatment is permanent & irreversible. It is often possible to tell if a stone has been heated to high temperatures by studying the inclusions within the stone. However some stones do not contain diagnostic inclusions, which could be used to prove treatment or non-treatment. Most of the rubies and sapphires available in the market place today have been treated using this method.

Surface Diffusion

The stone has been heated in the presence of colour bearing elements such as iron & titanium. During the heat-treatment process, the elements are diffused into the gem just below the stone's surface, thus creating a coating of colour. It is also possible to diffuse a ‘star’ into the surface of cabochon cut rubies and sapphires producing surface diffused star rubies or sapphires. The depth of penetration of the diffused colour coating or diffused star is approximately 0.1mm. The colour coating or star can be removed if the stone is damaged or re-cut. These stones can be detected by viewing the stone with a 10x loupe or microscope and/or by viewing the stone immersed in a heavy liquid such as Methylene Iodide (Di-Iodomethane).

From this diagram it is possible to see how the colour only penetrates the stone's sub-surface.

Beryllium Diffusion

The stone is heated in the presence of beryllium (Be) often in the form of chrysoberyl. During the heating process the beryllium is diffused into the stone and is probably acting as a type of catalyst, which triggers thermo-chemical reactions in the crystal’s atomic structure. The exact colouration mechanism of beryllium in corundum is still unknown. The depth of penetration of the Be- treatment can vary from just below the stone’s surface to throughout the entire stone. When the treatment is limited to the stone’s surface it can be removed if the stone is re-cut or polished.

Beryllium-treated orange/red sapphires.

A cross sectioned slice of a beryllium-treated sapphire.

A cross sectioned slice of a 'mad-pad' sapphire clearly showing the orange skin over the pink inner core.

The only accurate tests available today to detect beryllium are Secondary Ion Mass Spectroscopy or Laser Ablation-Inductively Coupled Plasma Mass Spectroscopy. Both these tests can be destructive and will leave marks on the stone's surface. These tests are expensive and availability is limited to specialised laboratories. There are other ways to detect beryllium-treatment. Some tests are strongly indicative others are diagnostic. Beryllium can react with some of the inclusions within the treated stone, creating new inclusions unique to Be-treated stones. Some of these inclusions can be similar to those found in stones that not been heated with beryllium but have been heated to very high temperatures. For this reason other tests should be performed for a more accurate identification.

Beryllium treatment is a process of diffusion. The depth of the diffusion can vary depending on the parameters used in the treatment process. Sometimes the depth of diffusion can penetrate just below the stone’s surface, other times it can penetrate the entire stone. If the depth of penetration is limited to the sub-surface of the stone, a layer of (orange) colour can sometimes be seen when the stone is immersed in a liquid with a similar refractive index like methylene iodide. It is also often possible to see this colour layer by immersing the stone in water.

The Beryllium Debate
	A few years have passed since beryllium-treated sapphires first appeared on the market. Beryllium treatment is now well known throughout the gem & jewellery trade and has received a lot of publicity. There has been much controversy since the treatment was first discovered which continues to this day. There are dealers who sell these stones without any disclosure of the treatment. There are some who try to mask the treatment by giving the stone a fancy name, like ‘padparadscha’ – a much-abused term.
The name ‘padparadscha’ is completely wrong and should never be used to describe a stone that has been treated with beryllium. It should be reserved for the natural coloured delicate orangey pink coloured sapphires. Some say the name padparadscha should be reserved for Sri Lankan stones of this colour, which have not been heat-treated. These are both a matter of opinion though as I have seen stones from other countries like Vietnam, which you would not be able to tell apart from the Sri Lankan stones.

At the opposite end of the nomenclature spectrum is the term ‘bulk diffusion’. The ‘bulk diffusion’ description although technically correct, it is too generalized to cover the treatment accurately. In our opinion beryllium-treated gems should be described as 'Treated' along with a brief description of the treatment, additives used and any special care required. Whatever these stones are called, they certainly should not be called described in any way as ‘padparadscha’. Other sapphires commonly treated with beryllium additives are yellow, orange and orangey/red colours.

Beryllium-treated pink/orange sapphires like these are sometimes misleadingly sold as padparadscha sapphires. If in doubt, contact your friendly (reliable) local gem testing laboratory. If you feel you have been mislead, then contact the Trading Standards Institute.

One of the biggest problems with the beryllium treatment is detecting and identifying beryllium-treated stones. At present there are only two tests available which can give 100% accurate results in testing for beryllium in corundum, Secondary Ion Mass Spectroscopy (SIMS) & Laser Ablation-Inductively Coupled Plasma Mass Spectroscopy (LA-ICP-MS). Both these tests are expensive and can cost several hundred dollars per stone. The cost means this test is completely impractical for many gems sold today. There has also been much talk of Laser Induced Breakdown Spectroscopy (LIBS) but although the cost of this test is much lower than the SIMS or LA-ICPMS tests, the level of error means it could not replace them.

The Conclusion

In an ideal world there would be no gem treatments. It should be understood that many gems are very rare and in some cases mined at only one location in the world. For this reason alone, if there were no gem treatments there would never be enough gems to satisfy the world demand. Untreated coloured stones are certainly the exception rather than the rule and their rarity means fine quality untreated gems command premium prices.

The subject of heat-treatment is very deep and would require far more than this website to discuss thoroughly. We have given a brief description of some more commonly encountered treatments to rubies & sapphires. If you would like to read about the subject further, we do recommend two books that can be ordered online from us. Click here for more information.