Diamonds are traditionally judged using the 4Cs – Colour, Clarity, Cut and Carat Weight. The first three are a measure of quality, describing how innately pure and brilliant the diamond is, and how well it has been cut. The last is simply an indication of size – this will contribute to the diamond’s value but has no bearing on its quality.
There are a number of individual steps and complex processes and procedures involved in the diamond valuation and certification services provided by National Diamond Valuers, including:
National Diamond Valuers grade your diamond against the universally-accepted colour grading scale developed by the GIA (Gemmological Institute of America). The GIA’s colour scale assigns a letter, ranging from grade D to grade Z, that indicates the colour of a diamond when it is viewed under precise conditions using controlled lighting, in comparison to a master set of stones with established colour grades.
The most highly-prized white diamonds are D grade, which are structurally perfect and chemically pure, having no colour whatsoever. The scale progresses through a subtle colour gradient, with differences often barely discernible to the untrained eye, from the colourless D grade diamond to the distinctly yellow- or brown-tinted Z grade diamonds. “Fancy-colour” yellow diamonds, such as the Champagne diamonds found in the Argyle range, are not Z grade white diamonds – rather they are graded on a different colour scale against a separate master set.
National Diamond Valuers uses two methods of colour grading. We utilise a GIA master set to visually compare your diamond to stones of established colour grade, in combination with a Gran DC3000 Mk2 colourimeter. The colourimeter quickly and accurately establishes the colour grade of loose and set diamonds, from D grade through all varieties of fancy-colour diamonds, using spectral analysis to measure colouration and to indicate the hues and tints of the diamond.
The term “fancy-colour” refers to naturally occurring diamonds that have a deep yellow, brown, red, pink, blue, or even green colour. The colour grade of these rare diamonds is based on intensity, rather than brilliance, with a more intense colour generally being more highly-prized than a paler colour.
National Diamond Valuers uses the Judge II Viewing Booth, whose patented light technology and multiple light sources allow better colour rendering and detection, in combination with either the GIA Coloured Diamond Grading Scale or the Argyle Grade of Fancy Coloured Diamonds (depending upon the colour and origin of the stone) to determine the fancy-colour grade of coloured diamonds.
The GIA scale describes colour in terms of hue, tone, and saturation. Hue refers to the basic colour (e.g., pink), while tone refers to how light or dark the colour is, and saturation refers to the depth or strength of colour. The GIA Coloured Diamond Grading Scale assigns grades ranging from Faint, Very Light, Light, Fancy Light, Fancy, and Fancy Dark, through to Fancy Intense, Fancy Deep and Fancy Vivid.
The Argyle colour grading scale assigns a combination of letters and numbers to indicate the hue, tone, and saturation. The original Argyle Colour Grading Scale describes yellow-brown diamonds ranging from C1 (pale yellow) to C7 (deep brown), with most champagne, cognac or chocolate diamonds falling within the C4 to C6 range.
Grading scales have also been developed for other colour ranges from the Argyle mine, including:
Grading of fancy-coloured diamonds is National Diamond Valuers’ speciality and we are fortunate to have unrestricted access to the only Argyle pink and red diamond master set in Australia.
The process that leads to diamond creation – i.e. the exposure of carbon to intense heat and pressure deep below the ground – can also result in the formation of ‘inclusions’ (also known as ‘internal characteristics’) and ‘blemishes’ (also known as ‘external characteristics’).
Assessing a diamond’s clarity involves evaluating the extent of these imperfections, including their size, number, location (position within the diamond), relief (level of contrast and visibility), and nature (type/key characteristics), and determining how these characteristics affect the diamond’s overall appearance.
The GIA Diamond Clarity Scale has six categories, some with subdivisions, resulting in a total of 11 possible grades:
Inclusions and blemishes are often so small and slight that they can only be identified with the help of magnification, by an experienced, trained grader. To the untrained eye, and without magnification, one diamond may look very much like another but can actually be of vastly different quality, which is why it is important to have your diamond accurately assessed and graded by an expert diamond grader.
The gemmologists at National Diamond Valuers use a combination of training, years of experience, and state of the art equipment that is capable of greater than 10x magnification to ensure your diamond is thoroughly examined and its clarity is properly graded, so that we can give you the most accurate valuation of your investment diamond. National Diamond Valuers plot all inclusions and blemishes and include this information in your valuation and grading report and Diamond Certification.
The grade of a diamond’s cut is determined by how well its facets reflect and interact with light to create the most desirable visual effects, such as:
A good cut is key to ensuring the best face-up appearance and, conversely, a poor cut will have a direct impact on the diamond’s quality and value. Faceting a stone so that it delivers the maximum sparkle and return of light requires incredibly precise workmanship and a thorough understanding of how to calculate the correct proportions, achieve the correct angles and symmetry, and polish the stone to achieve optimal shine and glow on the diamond’s surface.
As there are so many variables and considerations involved in achieving the best cut for each individual stone, a diamond’s cut is often the most technically difficult and complex quality to grade. National Diamond Valuers use the GIA Diamond Cut Scale, which assigns one of five grades: Excellent, Very Good, Good, Fair and Poor.
We use the latest technology, including the Sarin DiaMension and the Sarin Diascan in combination with Cut Grade Analyzer software, to examine the proportions of the diamond and get accurate measurements of all angles and facets. We can even generate 3D images to assess your diamond’s appearance under optimal light conditions, and evaluate its fire, brilliance, and scintillation.
The final factor in determining the value of your diamond investment is carat weight. A metric carat is a universally recognised measurement of your diamond’s apparent weight, defined as 200 milligrams. This weight is then divided into ‘points’, allowing a diamond to be precisely measured to one hundredth of a decimal place, with a full carat being 100 points.
While a larger, more weighty diamond will attract a higher price tag, as larger diamonds are rarer and more sought after, the value of the diamond is also dependent upon its quality. The grade of a diamond’s colour, clarity and cut, mean that two diamonds of an equal carat weight can vary considerably in value and price.
There are also diamond weights that are deemed “magic sizes” – these are half carat, three-quarter carat, and full carat. Magic sizes are another important consideration in assessing a diamond’s value and price. So, while there is imperceptible visual difference in size between a 0.97 carat diamond and a full carat diamond of equal quality, the price and value of the “magic” full carat diamond may be significantly greater.
As a diamond’s exact weight can factor heavily in determining its true value, National Diamond Valuers use precision instruments and the latest technology to accurately measure the carat weight of your diamond investment.
As part of the assessment process, National Diamond Valuers will perform fluorescence testing on your diamond, to determine its reaction to invisible UV-A light – i.e. how brightly it lights up when exposed to an ultraviolet light source (blacklight).
The degree of fluorescence exhibited by your diamond will be indicated on the grading report in terms of its strength, which will be noted as ‘medium’, ‘strong’ or ‘very strong’. Around 25% of diamonds exhibit some level of fluorescence, but studies conducted by GIA have shown that the strength of a diamond’s fluorescence has no appreciable effect on its appearance, nor does it affect the diamond’s structural integrity.
A variety of treatments may be used to enhance the appearance of your diamond, by increasing its clarity or improving or changing its colour, however these enhancements may also affect its value. A diamond simulant may also be enhanced by applying a thin film of laboratory-grown diamond to the stone’s surface, to give it some of the qualities of a real diamond.
In assessing the quality and value of your investment diamond, National Diamond Valuers will verify whether your stone is natural, created or simulated, and carefully examine the stone for evidence of any treatment that may have been used to enhance its appearance. Our state-of-the-art Judge II Viewing Booth enables our gemmologists to easily detect additives used to enhance or create colour, including brighteners, whitening agents, dyes, pigments, and other treatments.
While uncommon, colour treatments may be used to enhance the colour of a diamond. A diamond whose colour grade is poor may be coated with a thin layer of chemicals or plastics to mask the natural colour, or the colour of certain diamonds may be improved or altered by using a HPHT (high-pressure, high-temperature) treatment. Detection of HPHT treatment requires the expertise of a trained diamond grader using specialised laboratory equipment, which is why it is important to have your investment diamond examined by an experienced gemmologist.
The apparent clarity of a diamond may be improved through various treatments. One of the two main clarity-enhancing treatments is laser drilling, which is used to remove small dark inclusions. This treatment involves using a laser to drill a tiny hole in the diamond, either to burn away the inclusion or to bore a channel into which a bleaching agent can be infused.
The other main clarity-enhancing treatment is fracture filling, which is used to hide white fractures called ‘feathers’. A glass or resin-like substance is injected into the fracture to fill it, making the feather less visible. When this treatment is done well, it is difficult to detect outside of a laboratory, except by a skilled diamond grader.
After completing a thorough inspection and valuation process, and where your stone meets our strict quality standards, National Diamond Valuers can issue you with a Diamond Certification.
Your National Diamond Valuers Diamond Certification report is your guarantee that a renowned diamond grader and qualified gemmologist has conducted an unbiased, authoritative assessment of your investment diamond, and that you have been provided with an accurate and reliable professional valuation.
Your Diamond Certification is a printed report providing all the information you require about your diamond’s quality and value, including its colour, cut and clarity grade, carat weight, diagrams showing your stone’s precise dimensions and plotting your diamond’s characteristics, and confirming your stone’s geographic origin.