cutting remarks

Consumers are growing increasingly educated about the authenticity of precious stones and metals in jewellery. Here, ANU MANCHANDA takes us through the AnchorCert Gem Lab Report process.

Diamond certification is a hot topic. Demand is being driven by internet sales and research and the consumer’s perceived increase in knowledge as they try to assess one potential purchase against another based on ‘quality’ as opposed to the straightforward visual appeal of the stone.

The ‘4 Cs’, Clarity, Colour Carat and Cut, are widely understood at a basic level. Recently there has been much discussion with regard to varying standards of grading for colour and clarity and also concerns about the pollution of the natural diamond market with synthetic stones and artificially enhanced natural diamonds.

The quality of the cut is assessed by the diamond grader. Anu Manchanda, senior gemmologist for the AnchorCert Gem Lab, explains the features that can impact the quality of the cut and therefore the appearance of the polished diamond. “Cut is categorised by three things: shape, proportions and finish.

“Proportions are the angles and the relative measurements of a polished diamond’s facets and the relationship between them. The finish of a diamond includes its polish and the precision or symmetry of the cut. These factors affect the way that the light enters and is reflected by the stone, which determines the final brilliance and therefore the appeal and value of the diamond. Evaluating the cut is a major factor in grading a diamond, but it is not subject to the massive concerns over determining colour and clarity which the industry is experiencing at the moment.”

The modern Round Brilliant cut has been designed to produce optimum brilliance from the diamond and is well established as the most popular traditional cut. A standard Round Brilliant has 57 facets or 58 if it has a culet, but there are many branded alternatives with additional facets which purport to add sparkle to the stone.

The way a diamond is cut to certain angles and proportions will determine its beauty as well as its value. Most of the diamonds being cut in the marketplace today are cut to maximize weight retention which results in the diamond being cut either too shallow or too deep. If it is too shallow, light escapes from the sides causing the diamond to lose brilliance. If it is too deep light escapes from the bottom causing the diamond to appear dull and lifeless. An ideal cut will give the perfect balance of internal and external light refection.

The thickness of the girdle is an important consideration; a well cut diamond should have a girdle thick enough to prevent chipping. Seven grades differentiate the girdle, from ‘extremely thin’ to ‘extremely thick’ and the four ‘best’ are recognised as ‘very thin’ to ‘slightly thick’.

When a Round Brilliant diamond is cut to ‘ideal proportions’ with superior optical symmetry, polish and a specific faceting pattern and all these factors are in harmony, the result is a repeatable, near perfect pattern called Hearts and Arrows. Eight symmetrical arrows are seen in the face up position or crown view and eight symmetrical hearts are viewed in the table down position, or pavilion view. This can be seen by using a small, specially designed light-directing viewer called ‘Firescope’.

The cut of a diamond can be graded by judging a diamond’s optical attributes according to three elements – brilliance, fire and scintillation. Brilliance is the internal and external reflection of white light. Fire is the dispersion of white light into spectral colours. Scintillation is the combination of the sparkle and pattern in the diamond, the sparkle is caused by the movement of the diamond or the observer and the pattern refers to the dark and bright areas due to reflection.

Diamonds with good proportion, symmetry and polish will take the best advantage of the light and will show the maximum brilliance, fire and sparkle. Based on these, optical attributed GIA Cut Grade nomenclature ranks from Excellent, Very Good, Good, Fair to Poor.

In recent years properly equipped Labs such as AnchorCert have invested in sophisticated equipment such as the Sarin DiaMension which profi les the diamond by passing light and viewing through a camera lens as it slowly rotates. This allows the machine to accurately record every necessary angle and measurement in order to determine the quality of the cut using the ‘GIA Facetware’ software which very accurately estimates the Cut Grade for the Round Brilliant Diamond.

The graders will always sanitycheck (a basic, manual test to quickly evaluate whether a claim or the result of a calculation can possibly be true) the outcome to ensure it matches their expert opinion before completing the report. All other cuts will have their quality assessed by the grader applying their expertise to the various measurements and proportions they have taken.

In extreme examples a poor cut can create some strange phenomena. Round Brilliant cut diamonds with a pavilion depth of less than 40% will show the refl ection of the girdle in the table. This is called ‘Fish Eye’. If the pavilion depth percentage is over 48% then the light leaks out of the pavilion and gives an eff ect of a dark circle covering a part or whole of the table area. This is called ‘Nail Head’. As their names suggest these diamonds are not admired and will be of relatively low value.

Assessment of the polish of a diamond is more subjective and encompasses the overall condition of the facet surfaces of a fi nished diamond. Its quality is aff ected by polishing lines, burn marks, abrasion, nicks and other imperfections which impinge upon the appearance of the diamond. Only when all of these factors have been assessed can the grader report on the cut.

Fancy-shaped diamonds can be graded for cut in the same way as Round Brilliant but the overall look of the fancy cuts is more important than the specifi c details considered for a round brilliant. They are more known to be selected for the appeal of their shape. For example, Oval shapes look bigger than Round Brilliants of the same weight, Triangular Brilliants off er good light performance. Shapes like Pear and Marquise can be graceful and stylish, while Heart shaped diamonds are the ultimate romantic gift. Jewellery for men is more likely to use the heavier lines of Princess and Emerald cuts.

Whatever the shape, an excellent cut with excellent polish and symmetry ratings is what truly creates the value of a finished diamond.