High Pressure High Temperature Treatment
Continuous developments in technology have created different treatment techniques used to improve the appearance of diamonds.  The colour of particular types of diamond can be altered artificially by subjecting them to conditions of extreme heat and pressure. The colour of a diamond following HPHT- treatment is dependent on the exact conditions used and the diamond type. The HPHT process is perfectly acceptable so long as it is disclosed to the purchaser.

Scientists divide diamonds into various types. The vast majority (over 97%) of diamonds handled by the jewellery industry are called Type I. A tiny minority of diamonds (approx. 2%) are called Type II.

These two types can then be further classified into Type Ia and Ib, and Type IIa and IIb.

HPHT deals with Type IIa diamonds which have no nitrogen and are colourless. These Type IIa diamonds due to  crystal lattice defects sometime show brown colour. Putting the diamond under high pressure and high temperature results in a repaired crystal lattice, and a colourless diamond.

In Type Ia diamonds the HPHT process causes dispersion of paired nitrogen into single nitrogen molecules and cause the diamond to take on a colour of fancy yellow to yellow-green. This transforms a unsaleable poor coloured diamond into a valuable fancy coloured diamond.

HPHT- treated diamonds are impossible for gemmologists to identify using standard gem testing instruments and therefore, undisclosed HPHT- treated diamonds are a great concern to the gem and jewellery industry. However, AnchorCert has invested in the latestest technology which can help identifiy HPHT-treated diamonds. All diamonds submitted to AnchorCert are screened and examined to ensure they are natural. If a diamond shows signs of having been exposed to treatment, further tests would be carried out to identify if the stone had been subject to HPHT treatment. AnchorCert are the only UK diamond grading authority equipped to identify this.

CVD - Chemical Vapour Deposition
Chemical vapour deposition, developed in the mid 1980’s is a process by which incredibly thin films of diamond a few microns thick can be generated and deposited on a base.  The process involves high temperatures (over 2000°C) and lower pressures than involved in HPHT. Mixtures of hydrogen and hydrocarbon gases are energised with heat or electrical energy in a deposition reactor. The carbon molecules are deposited on a substrate as a thin film of polycrystalline material. 

Quality and purity are very high and particular diamond properties can be selected.  Boron added to the growth gases, for example, will produce an electrically conducting diamond.  When the diamond layer has reached the correct thickness the reactor is shut down and the CVD wafers can be removed. Single crystal diamonds can also be grown, but sizeable gem quality is proving difficult. All CVD diamonds are believed to be Type IIa diamonds as no nitrogen is present.

CONFLICT DIAMONDS - THE FACTS
Environmental and Humanitarian Issues are of increasing concern to the consumer.  Many are now seeking reassurance that the goods they are buying have been produced in a responsible manner and that the people involved in the supply chain have not suffered in any way.

This is of particular concern to many when buying high value luxury items as an expression of love and commitment.
It is true that in the past “conflict diamonds” have been a source of revenue which has funded civil conflict in countries such as Sierra Leone and Angola. This problem was recognised in 1998, following a decade of violent conflict in the continent of Africa. Concern from non government organisations such as Global Witness and the jewellery trade itself resulted in a United Nations resolution in 2000 and the establishment of the Kimberley Process in 2002.  The Kimberley Process has been adopted by 68 governments worldwide and regulates all rough diamonds. It is now estimated that only 1% of the annual production of diamonds are traded outside the Kimberley Process. All responsible UK retailers will require that diamonds have a Kimberley certificate to ensure that they are not conflict.

For more details visit www.kimberleyprocess.com

The mining of diamonds and gold employs millions of people in the world’s poorest areas, particularly in Africa, and in India a further 700,000 are employed in the diamond cutting industry. It is crucial to the survival of these people who in most cases have no alternative source of employment or income.
The Western consumer spend on gold and diamonds is keeping millions alive. If this spend should fall for whatever reason it would have severe consequences for many communities and cause untold suffering for the people of Africa and their families This particularly applies to those in areas where long term conflict has devastated the economy and the population are struggling to recover and survive..

The facts are:

• The Diamond  industry alone employs 10 million people globally
• As two of its major resources diamonds & gold are helping transform Africa & the lives of its people
• Income from diamonds and gold make a difference in the developing world by providing jobs, roads, healthcare, education
• The Kimberley Process has significantly reduced the amount of conflict diamonds in circulation
• Major players at every stage of gold an diamond supply chain have committed to taking a more responsible approach

For more information visit www.diamondfacts.org or www.responsiblejewellery.com

Cobalt Coated Tanzanites
AnchorCert detected examples of tanzanites which had been enhanced by the latest process – cobalt coating. The treatment takes the form of a surface coating which can improve the apparent colour of the tanzanite by as much as two grades, ie from A or AA to AAA or AAAA. The colour enhancement makes the stone apparently better quality, and therefore more valuable, than it was originally. However, the cobalt can be polished off and the treatment should definitely be disclosed by the seller.

The treated stones detected by AnchorCert were between 30 points and one carat and the supplier knew that the stones would be submitted for certification. This suggests that some of the supply chain is buying and selling in good faith and is not yet aware of the new treatment, which only became available commercially within the last 12 months. The cobalt treatment is sometimes quite hard to identify with a 10x loupe, but under higher magnification, using a gemmological microscope there are give away signs. AnchorCert gemologists automatically look for the signs and if the coating is in any way imperfect they are easy to spot.

On a perfect example the only way you can tell with the naked eye is by the colour, which just doesn’t look right. When checked with a loupe you can see that the colour is patchy, particularly when viewed from the crown, and when the stone is put under X –Ray Fluorescence it will show relatively high levels of cobalt.

DIAMOND TREATMENTS – AN EXPLANATIONFROM ANCHORCERT

How do they do that?
Diamonds are a natural product and their quality varies widely, which in turn affects their value significantly. The diamond trade has always sought ways to improve less valuable, potentially unsalable, diamonds by enhancing their colour or clarity. Anu Manchanda, Senior Gemmologist for AnchorCert, the diamond certification division of The Birmingham Assay Office, explains how the most common enhancements are carried out and the tell tale signs which helps gemmologists to detect them. All of the practices described below are accepted by the trade but must be disclosed so the customer knows they are buying a treated diamond and pays the appropriate price.

Diamond treatment usually involves improving the total quality of the diamond by modifying the inclusions and/or enhancing or changing the colour. Some treatments are stable and permanent while others may not be that stable and can suffer damage during setting, wear, cleaning and repair.

CLARITY TREATMENT

Fracture Filling
Cracks and fractures in a diamond reduce its clarity, but can be treated by filling. Fracture filling utilizes a glass-like material which has similar optical properties to that of diamond. It will improve the diamond’s appearance by almost two clarity grades but is not a permanent treatment. Most obvious evidence of fracture filled diamonds is bright flashes of changing colour that can be seen under proper lighting. Other evidence is presence of bubbles in the fracture of the filler or ‘crackled appearance’ of the filler. All these can be picked by 10 X magnification.

Some recent more advanced fillers may not show the colour flashes. This fracture filling can be confirmed by X-rays; diamonds are transparent to x-rays while the glass filler is not and will show an image on the photographic plate. It is general practice that gemmologists will not apply a colour or clarity grade to fracture filled diamonds.

Laser Drilling:
Laser drilling is used to reduce the visibility of natural inclusions. A hole is drilled using a laser beam, with a diameter less than 0.02mm, through the diamond to reach the inclusion. Carbon-di-oxide lasers are used to heat a tiny area of the diamond until it evaporates, forming a tube reaching the inclusion. The inclusion is then vaporised with laser, bleached or etched with acids. The inclusion becomes less apparent, makes the diamond more saleable but it is still present. Laser Drilling is a permanent treatment and has become prevalent in smaller stones. It can be detected with 10 X magnification and the microscope. Sometimes laser drill channels are glass filled and they show colour flashes. Diamonds that are both laser drilled and fracture filled are not colour and clarity graded.

Internal Laser Treatment:
In Internal laser treatment there is no drill hole or drill channel present but the laser leaves a worm like squiggle; this treatment is also known as KM treatment. KM stands for ‘Kiduah Meyuhad’ in Hebrew meaning ‘special drill’. This treatment is used on black inclusions which are accompanied by internal fractures. One or more pulses of the laser beam is focused on the inclusion with the resulting heat creating an internal fracture. The inclusion is then bleached by boiling the diamond in strong acid under pressure. The created feather is very difficult to differentiate from the natural feather; but it can be easily spotted under high magnification of a microscope using different lighting techniques by an experienced diamond grader/gemmologist.

COLOUR TREATMENT
Surface coating: Surface coating applies a thin layer of coloured foreign material to all or part of a diamond surface, to either mask the underlying body colour or enhance a desirable colour. Most often, this coating is applied to the pavilion and/or girdle of the diamond; the way that light refracts as it passes through a diamond then creates the illusion of uniform colour distribution. The durability of diamond coatings vary considerably, depending on materials used and methods of coating applied. Most recent advances in technology employ a very thin optical or chemical film which is more durable than older methods, but still readily worn away by heat, scratching, abrasion, polishing, and just everyday wear.
The coating, if damaged; can be picked up under microscope by an experienced diamond grader/gemmologist.

High Pressure High Temperature Treatment (HPHT):
HPHT treatment is mostly applied to Type IIa diamonds which have no nitrogen and are usually colourless but due to distortion of crystal lattice sometimes show brown colour. Exposing the diamond to high pressure and high temperature eliminates the brown colour by reducing or removing the structural irregularities in the crystal lattice.

In Type Ia diamonds, of brown colour, the HPHT process causes dispersion of paired nitrogen into single nitrogen molecules and causes the diamond to take on a fancy yellow to yellow-green colour. This transforms an unsalable poor colour diamond into a valuable fancy colour diamond but this is usually easily detected as the stone will have a a strong reaction to ultra violet light that helps to identify the HPHT treated fancy yellow-green diamond. The HPHT treatment is detected by testing the Photoluminescence using Raman spectroscope under liquid nitrogen temperature (-196°C)

Irradiation & Annealing: Radiation from high energy particles is used in creating colour centres in diamonds. These radiations alter or damage the crystal structure and change or intensify colour. The most common colours caused by irradiation are different hues of blue and green. Heating (annealing) the diamond after bombarding it with charged particles results in the modification of the bluish green colours to yellows, oranges and sometimes pinks, reds and purples. Depending on the type of radiation used the colour may be restricted to the surface or penetrate the whole stone. This is a stable treatment under normal situations. The treatment can be detected by testing the absorption spectrum using UV-Vis Spectrophotometer and Photoluminescence using Raman spectroscope under liquid nitrogen temperature.

Heat Treatment, Graphite Treatment: Low quality, heavily included diamonds are heated in a vacuum to form graphite deposits within the fractures, resulting in black diamonds. The majority of black diamonds found in the diamond market are treated and spectroscopic methods are used to authenticate the origin of colour.
Multiple treatments on diamonds have become common. AnchorCert gemmologists see examples of these treatments on a regular basis and use their sophisticated equipment to ensure all treatments are disclosed as required.

Focus on the Expert

Anu Manchanda MSc, GG, DGA, FGA, P J Dip, F.N.A.G. Pearl Graduate (GIA) - Senior Gemmologist
Anu Manchanda holds a Master degree (MSc) in Geology from India, an FGA, DGA from the School of Jewellery, Birmingham and the Professional Jewellers’ Diploma (PJ Dip) with distinction from the National Association of Goldsmiths. She is also a Fellow of The National Association of Goldsmiths (FNAG) and a Pearl Graduate of the Gemological Institute of America. She is recipient of the Christie’s Prize for Gemmology (2004). This is a trade prize awarded to the best candidate of the year who derives his or her income from activities essentially connected with the jewellery trade. Anu tutors for the Gemological Association of Great Britain’s Correspondence course students for both - the Diamond Diploma & Gemmology Diploma courses (DGA & FGA). As an AnchorCert ‘Senior Gemmologist’ Anu is responsible for accuracy and for new initiatives in the diamond grading and gem testing laboratory. The specialized equipment such as the Raman Spectroscope, FTIR, SSEF Diamond Spotter, Diamond View, Diamond Sure, Sarin-DiaMension, and Colorimeter, required for the identification and correct grading of diamonds and gems and their synthetic counterparts are all used in the AnchorCert Laboratory under her guidance and direct supervision.

The Birmingham Assay Office was founded in 1773 to provide a hallmarking facility to the rapidly expanding local silver trade. Over 235 years it has become established as the largest UK Assay Office. During the past decade the Assay Office has expanded its services further, far beyond its statutory Assaying and Hallmarking duties and offers independent expert opinion on every aspect of the precious metal, jewellery and gemstone trade.