Treatment of coloured Gems

Gemstones can be treated and enhanced for a more pleasing visual effect, using methods that have existed for centuries. Undetectable and permanent enhancements ensure that there are always beautiful gemstones in the market. If these treatments are stable, the stone’s value increases. Treatments that are less stable should be avoided. It is important that buyers are educated on the different types of treatments available, whether the treatment produces minute changes or dramatic change. One example of this is colourless topaz – irradiation and heating of colourless topaz permanently transforms it into blue topaz.

Three Colors of Irradiated Topaz, Brazil
(Photo by ICA/Bart Curren)

Treatment is usually performed by the cutter, or lapidary, who after obtaining a rough gem wishes to sell the most valuable gem possible. Since many treatments are performed in the countries which cut and mine the stones, disclosure of the treatments may not always happen. Sapphires and rubies, for example, are often heated before the rough stones are sold to the cutters.

Since details of treatments are not always given, a buyer must be informed. The price alters depending on the type of treatment and the type of stone itself. Some gemstones require enhancement to be sold at all. Citrine and tanzanite are naturally rare – only with a heating treatment is there enough supply to meet demand for these stones.

Some gemstones do not require enhancement by present technology at all: Garnets, peridot, iolite, spinel, all varieties of chrysoberyl, catseye tourmaline, malachite, hematite, and all feldspar including all varieties of moonstones. In the future this may change, as new technologies and methods of treating gemstones change every year.


Heating is the most common treatment, and can lighten, darken or clarify gems. Rarely, colour is changed completely. It is fair to assume the following are heated: rubies, sapphires, tanzanite, citrine, pink topaz, aquamarine, and blue and colourless zircon. Tourmaline and amethyst are occasionally heated to a lighter colour.

Irreversible and almost undetectable, heating often enhances the appearance of the gem and there is rarely a great price difference. Indeed, some gems are almost worthless without heating, such as tanzanite, citrine, pink topaz, blue and colourless zircon. Rubies and sapphires which have not been heated sometimes contain microscopic rutile needles or tiny gas bubbles in pockets of liquid, which are detectable by the right people. It is extremely rare that these unheated gems are of good colour – those that are will be sold at premium prices.


Oiling is most commonly used on emeralds. They are stored as rough emeralds in oil, and oil is used as lubricant when they are cut, allowing the oil to penetrate any fissures on the surface and render them less visible. If there are no fractures on the surface, no oil penetrates the emerald and if the colour is consistent the stone will fetch a premium price. Oil may be leached out of the emerald if it is steamed clean or put into an ultrasonic. Since this can result in the fractures reappearing, the emerald can be re-oiled.

Low-quality rubies are oiled, and coloured oil is used to add colour and conceal fractures on other stones. This is uncommon among reputable jewellers, but something to avoid as the true colour is unclear.

Fractures are also often filled with synthetic resins and hardeners, a more permanent solution than oiling.


Irradiation is the process of exposing the gemstone to subatomic particles or radiation. It is sometimes followed by heating, which changes the colour. This is commonly done to blue topaz, rare and pale in nature but available at reasonable prices in different shades after irradiation. A natural blue topaz of fine colour would, of course, fetch a higher price without treatment.

Tourmaline is sold at the same price after irradiation, to darken pink stones into red ones, identical to the red tourmaline found naturally.

Irradiation and heating can create diamonds of intense greens, yellows, blues and browns. Ask the seller about treatments if you wish to purchase a fancy coloured diamond, particularly green, for they should be sold for less than natural diamonds of similar colour, cut, clarity grade and size.


The benefits and disadvantages of dyeing depends on the variety of stone. Black onyx would not exist without dyeing, nor would the more intense colours of pearl and agate. After dyeing, colours are more attractive, though they lack the edge that naturally coloured stones have. In short, it is fine to purchase a dyed gem, as long as you know that it has been treated and there is no deception.

Dyeing becomes less acceptable when it is done to disguise poor quality – this often happens to jade, lapis lazuli, turquoise and coral. Some can be tested – rub lapis lazuli with cotton and acetone, and you will see blue on the cotton if it has been dyed. Fine, if the seller has told you. Compare the price of the real thing to the dyed and make your own decision as an informed buyer. Beware a price that is ‘too good to be true’. Some materials are more difficult to test, such as coral and jade.

Surface diffusion

Surface diffusion is the infusion of chemicals onto a sapphire with heat. This improves its colour or creates asterism (where light reflects off the stone in a star shape). The colour can be removed, and must be removed if the stone is to be repolished.


Surface fractures or cavities can be filled with glass, plastic or other materials. Rubies are often filled. It takes close magnification to spot the differences in surface lustre that indicate a will to deceive the buyer. It is difficult to know what the price should be, due to the enhancement covering the true quality of the gem.

‘Yehuda filled diamonds’ entered the market within the last few decades, but again, is only acceptable when buyers are informed of the treatment. To begin with, diamonds with such cracks that are easily visible are of a poor quality. Filling covers this up, but it doesn’t change the quality of the stone and the filling can melt back out during any repairs if the jeweller wasn’t told about the enhancement. The price should reflect the true quality of the gemstone, even with its visual enhancements.


Lasering is the drilling of minute holes into a diamond to provide access to an inclusion which can be bleached to improve a stone’s appearance. It is a rare practice, and easily visible under magnification. Slightly imperfect, and imperfect diamonds, are the types which are lasered, and their clarity grade, and price, should not change.

Enhanced vs Natural Diamonds

Purchasing loose diamonds can be an investment for the future, so it’s best to choose diamonds that will hold their value in the long term. Although you may not be concerned about the resale value of your diamond at the time of purchase, you may be interested in selling your diamond or trading it in for an upgrade later. When buying a diamond, it is best to know what contributes to its quality and value to ensure that you make a sound purchase. An important factor to consider is whether to buy a natural diamond or a treated or enhanced diamond.

Buying Enhanced and  Treated Diamonds

The subject of clarity enhanced , laser drilled and fracture filled diamonds (detailed below) is very controversial in the jewellery trade, especially for First Class or Master Jewellers. The term “enhanced” may sound like a positive feature, however, any diamond that has been enhanced has been treated and altered from its natural condition to artificially improve its appearance. If you decide to purchase an “enhanced” diamond, find out what kind of treatments have been used and how they might affect the value and care of the diamond.

Diamonds can be easily damaged because of this treatment both in manufacturing  and repair. It is vital that you, the customer, inform us when you have a treated diamond when it comes in for repair. If it is not a diamond supplied by us and it is treated, special care must be taken or it will break.

When buying these diamonds, you should know that enhanced diamonds are of average colour and very low quality, such as an I1,I2 or I3 diamond. It is important to understand the class of your diamond. If an I1, I2 or I3 diamond has been clarity enhanced to and classed as a VS diamond, the certificate must indicate this so the customer pays the appropriate price. An I2 diamond with a certificate stating it a clarity enhanced VS diamond is still an I2 diamond – you cannot buy a VS diamond for I2 prices. Likewise, you should not pay VS prices for an enhanced I2 diamond.

Most reputable or high class manufacturing and retail jewellers stay away from these diamonds as they are more trouble than they are worth. It is usually the cowboys, fly-by-nighters and internet sellers in the industry  that sell clarity enhanced  diamonds.

Diamonds, like gold, are the same price all around the world. It is only the markup of the jeweller and taxes in each different country the give them a price difference. The old saying is: If seems too good to be true, it is – particularly with diamonds. You only get what you pay for, and you should always look at the diamond before you purchase it. Most importantly, look at the quality of work a diamond seller is producing to see if you can trust them. Many of my customers have purchased a ring from these cowboys only to find the ring is poorly made and end up paying an added cost of having it properly remade. Take the time, get to know your jeweller and you’ll end up enjoying your jewellery for years to come.

Natural Diamonds

Made from carbon, diamonds are the hardest known substance to man and are both a naturally occurring and manufactured abrasive. Natural diamonds form at high pressure and temperature conditions existing between 85 to 125 miles in the earth’s mantle. It takes a diamond 1 to 3 billion years to form beneath the earth. Once formed, a diamond travels to the earth’s surface via streams of molten rock. Throughout this process, natural diamonds acquire inclusions and flaws within them that give them their own unique “fingerprint”.

Diamonds can be purchased in various sizes (carats), shapes, colours, and clarities. Natural diamonds are preferred over enhanced or treated diamonds because of their rarity and individual fingerprint. No two natural diamonds in the world are identical; each one is unique whether by colour, clarity or both combined.

Enhanced or Treated Diamonds

Enhanced diamonds are natural diamonds that have had very specific treatments done to them to improve their characteristics, or their natural “flaws”. One type of treatment is laser drilling, which is a process that removes minor inclusions in a diamond to produce a clarity enhanced diamond. This process will typically create lines that resemble tiny trails, which are visible under side-view magnification. The laser may dissipate the imperfection, or chemicals may be injected into the resulting tunnel to bleach away the colour. This is a more permanent process than fracture filling. However, it is highly debated whether or not this process damages the integrity of the diamonds, thereby decreasing the value of clarity enhanced diamonds in the long term.

Fracture filling is a treatment that adds a glass-like resin material to a natural diamond to close small cracks. Since the filling has the same optical illusion and refraction index as a natural diamond, it’s nearly impossible to detect the “repair” to the flaws, so you must inform your jeweller of the enhancement when you bring your item in for cleaning or repairs. Fracture filling is not a permanent treatment as heat from future repairs, cleanings, and even sunlight can erode the filler or possibly darken its colour, making the diamond less valuable as time goes on.

One other type of enhancement treatment is called HPHT (High-Pressure High-Temperature). HPHT is a treatment process that General Electric developed to permanently change the colour of a diamond. First used to turn yellowish diamonds into “fancy” coloured diamonds, this process is commonly used to turn yellow or brown diamonds into colourless diamonds to be sold at a significantly higher prices. HPHT involves putting a diamond into a pressure chamber and squeezing it at high pressure and high temperature for a short amount of time. Although some feel that this treatment should be considered a standard technique and claim that this process is just finishing the job that nature started, the Federal Trade Commission feels that it is an artificial process and requires that HPHT be disclosed. It is also extremely important that jewellers know about this enhancement when working on an item with such a diamond. When HPHT treatment is detected in a diamond, the Gemological Institute of American (GIA) notes it on their reports as “HPHT Annealed” or “Artificially Irradiated” and insists that such diamonds be laser-inscribed with the same designation. A diamond that has been enhanced by General Electric will be inscribed with the symbol “GE POL”.

When considering the purchase of an enhanced or treated diamond, you should also be considering the long-term care and appearance these enhancement treatments may have on the diamond. Enhancements sometimes result in discolouration or cracks in the diamond which can result in breakage if a jeweller is reworking the diamond without knowledge of the treatment.

Take your time and consider carefully. Learn about the seller and their reputation, and upon purchase, be sure to collect the right documents and know just what kind of diamond you are purchasing. Above all, remember to tell your jeweller if your diamonds have had treatments.

Coloured Diamonds

Champagne Diamonds

Champagne and Cognac diamonds are the best coloured diamond buys, at around one third the price of white diamonds. These good prices will not last forever.

Prices for colours C1 to C6 are all about the same. Lighter stones are popular because they sparkle a lot and cost less. More intense colours are also popular because the colours are so beautiful, so supply and demand are fairly balanced. You can simply choose the colour you like best without worrying about which is more valuable. However, it is important to know about the many different secondary colours. In general, warmer colours are more attractive than grey-greenish browns. Intense golden and rusty colours are called fancy Cognac, or C7 and cost a little more. Naturally champagnes with a pinkish tinge are the most sought after and expensive.

Blue Diamonds

Natural blue diamonds are a light greyish blue shade, a more “steely” colour than sapphire. The most famous blue diamond is the “Hope” diamond in Washington’s Smithsonian Institute. This stone is steeped in legends. Its last owner was New York jeweller Harry Winston, who purchased it to donate to the Smithsonian and only owned it for one day. While his insurance company and armed couriers were discussing the cost and method of delivering the priceless gem to Washington, Harry strolled down to the post office and posted the diamond in a cigarette packet as ordinary mail.

Green Diamonds

Green diamonds have come into contact with radioactive minerals such as uranium. Radiation stains the outside of the diamond, so the cutter must be careful not to cut away too much of the green “skin”. Laboratory analysis is needed to authenticate that the radiation occurred naturally. Buyers beware!

Yellow and Orange Diamonds

To be called a Fancy colour means the diamond has more colour than Z on the GIA D-Z white diamond grading scale. Fancy yellow diamonds come in a range of hues from greenish yellow to amber. They start at similar prices to white diamonds, but the prices grow as the intensity increases. Connoisseurs in the trade use the term “canary” to describe intense yellow. Burnt orange Argyle champagnes are a less expensive alternative to very expensive pure gold or orange colours.

Black Diamonds

Pave set black diamonds are popular in Europe at present. We think they make great men’s jewellery for Aussie blokes, and we have a range of understated rings and cufflinks. Most of the black diamond fashion jewellery is made with treated coloured diamonds. Black diamonds with a good surface lustre are rare.


Colour plays a major role in determining the quality of a diamond. A diamond acts as a prism, dividing the light into a spectrum of colours and dispersing this light as colourful flashes called Fire.

White diamonds, although they appear colourless, can have tinges of yellow and brown. As these tones become more easily apparent, the rarity and value of the diamond decreases. D is the highest grade & indicates a completely colourless diamond.

Strong coloured diamonds called Fancies have colours ranging from intense yellow through to blue, green, pink & red. These diamonds are extremely rare & valuable.




The clarity or purity of diamonds is determined according to the effect that inclusions and marks (imperfections inside the diamond) have on the appearance of the stone when viewed face up at 10x magnification.

To determine the clarity grade of a diamond, the size, colour, number, location and visibility of any internal inclusions or external markings must be taken into account. Inclusions are ranked on a scale of perfection, ranging from Fl (Flawless: no internal or external inclusions visible under 10x magnification) to P (Pique) or I (Included) inclusions visible with the naked eye. If the inclusions are not visible to the naked eye, the diamond is deemed eye clean.

The position of the inclusions is important in choosing a diamond. Some inclusions at or near the edge can be hidden by a mount and therefore have a lesser effect on the beauty of a diamond. An inclusion in the middle or top of a diamond, however, could be more visible and have more impact on its appearance making the diamond less attractive.



Carat Weight

The weight of a diamond is always expressed in carats (one carat equals 0.2 grams). This is further broken down into points: 100 points equals one carat. Diamond weight is recorded to 2 decimal places in carats, or as the number of points. For example, a half-carat stone can be described as 0.50ct or 50 points




The cut (make) of a diamond is a most important feature. Cut is not a reference to the shape of the stone. It refers to the angles and proportions created by the skilled craftsperson while transforming a rough diamond into a polished diamond. A diamond may have the highest colour and clarity, but a poor cut will result in a dulled brilliance.

A well-proportioned diamond follows strict mathematical proportions. The light entering the diamond from the top will be internally reflected from one facet to another before refracting back through the top, & returned to the eye of the observer, giving the stone maximum brilliance, scintillation and fire.

A diamond can be cut to retain maximum weight and to create the illusion of size, but this results in a loss of brilliance. If cut too deep, light will escape through the bottom facets and the centre of the diamond will appear dark. If the stone is cut too shallow, the light will also escape through the bottom facets, giving the diamond a watery or glassy appearance.

A well-cut diamond will internally reflect light from one facet to another and disperse and reflect it through the top of the stone, maximising brilliance as well as fire of the stone.



Argyle Diamonds

Pink and Red Diamonds

Before Argyle, most pink diamonds were a pastel shade worthy of passing interest, but not lasting passion. This all changed when the first Argyle Pink diamonds were released in 1985. Australia’s Argyle mine in the north of WA produces almost all of the world’s red and pink diamonds. Although it is the worlds largest diamond mine, most of its diamonds are champagne and cognac in colour. Around 0.1% are pink.

Scientists still do not fully understand the cause of the pink colour. Usually colour is caused by impurities, but Argyle diamonds are very pure. They are found in a rock called Lamproite that appears to have had a particularly violent journey through the earth’s crust. All other diamonds are transported to the earth’s surface in a rock called Kimberlite. This unique host rock means it is unlikely another mine like Argyle will ever be found. So when Argyle dries up, its goodbye to pink diamonds!