Diamond Grading Techniques

Today when searching for the perfect engagement ring, chances are you will be faced with the question of whether you should choose an engagement ring which has a certificated gemstone, or whether you should opt out. The diamond grading technique is a specialist service. The question is; what does it mean to have a certificated gemstone and how does it become certified?

Colour

When a diamond is tested for its colour grading there are several processes involved, however the approach and equipment used differs from one laboratory to the next. The colour of a diamond is usually best assessed by studying the gemstone through the pavilion with the table upside down on a white surface. Many graders grade diamonds using a set of masterstones. This set of pregraded masterstones usually consist of five diamonds in two grade increments e.g. a E, G, I, K and M. Each stone shows the least amount of body colour that the grade colour could exhibit and will be compared to the diamond being assessed. The intermediate grades will be assessed according to the graders own judgement. This is a largely subjective process however and is dependant upon the graders skill in this area, there are however several devises which are also used by laboratories to aid determining diamond colour grades. The Gran Colorimeter for example can very accurately and impartially determine a diamonds colour, and is even able to produce results which impart how high or low the gemstone is in this grading category.

When looking at the colour of a diamond, a specialist grader will often study the fluorescence of the gemstone. Fluorescence is a term which is applied to a diamond which has a colour reaction when exposed to long-wave ultraviolet light. This is a rare trait and approximately 65% of diamonds exhibit this characteristic. This can be a great thing if you are trying to work with a limited budget as it could accommodate you to be able to choose something closer to the colour grade you would like to purchase ideally. This is because diamonds that fluoresce a blue colour tend to appear to have a whiter colour when exposed to daylight, therefore if a customer chooses a lower-colour diamond with strong fluorescence it means the stone will appear to be more colourless than it is as some of the yellow body colour is cancelled out in the daylight.

Clarity

The clarity of a diamond is usually assessed by examining the gemstone with a loupe of 10x magnification or with a microscope. Professional graders often use darkfield illumination when observing the diamond. This is a procedure which concentrates light onto the pavilion in order to reveal or ‘light up’ the inclusions. If the diamond you have chosen for your engagement ring has been certificated it will be assessed not only for the presence of inclusions, but their placement, nature and how they affect the beauty of the gemstone.

Cut

Today there are several tools which can be used by grading laboratories to aid in categorising a diamond (some jewellers also use this equipment) e.g. an Angular Spectrum Evaluation Tool (ASET) which looks at the way light behaves within the stone as a measure for judging the success of the cut, DiaVision software scans an individual diamond and provides on-screen measurements and images which can be exported to a CAD system to aid in the design process, the GIA also have a programme which can be downloaded which is known as the GIA Facetware Cut Estimator which estimates the grade your diamond is likely to be using your input of data, though sadly this can only be used for brilliant cut diamonds.

The quality of the finish of the diamond is also very important; graders will take into account any marks the diamond may have on the outside which have been made when it was cut, as well as girdle fringing or bearding. A fine gemstone cutter is able to cut the gemstone whilst preserving as much of the gemstone as possible, occasionally diamonds may have markings on them which were present on the rough piece, which shows evidence that the cutter has been very careful about maintaining the mass of the gemstone. There are several non-contact scanning devises today which are used by laboratories including the AGS and IGI which can aid in impartially grading the quality of a diamond cut such as the DiaMension and Helium Scanner.

Marcel Tolkowsky developed a mathematical formula in 1919 for cutting diamonds to the ideal dimensions in order to create the perfect balance of fire and brilliance, today however this is considered far to simplistic and most of the gemmological institutes have their own (an often changing) notion of what makes the perfect cut, and they are continually creating new cuts to show off a diamond as they feel it should be done e.g. there are several current ‘designer cuts’ such as The Passion Flower cut, The Excalibur cut and the Jubilee cut. This means of course that there is a huge range of cuts for customers to select from so budget-willing they can select a cut which really suits them, even if they are after an old cut such as an old-mine cut, or rose cut. The round brilliant cut engagement ring is the most popular choice for jewellery, and is a particular favourite for wedding jewellery. It is known for bringing out the natural fire of a diamond and it’s available in a whole variety of shapes. Brilliant cuts are the only cut that can achieve total internal reflectivity. The princess cut is the second most popular gemstone cut. In simplistic terms it is considered to be a square version of the brilliant cut. It is particular suited to rough diamonds that have allot of depth to them. It is generally believed that the squarer the cut is, the better the quality of the cut is. The emerald cut is another popular traditional gemstone cut and known as a step cut. This type of cut is known for exposing the clarity of the diamond as the inclusions are not hidden by multiple facets, when adding a customer it maybe advisable to suggest a higher level of clarity such as a VS gemstone. They tend to be less sparkly than the previously mentioned cuts as they have fewer facets and as a result allow less refraction of light. These are the most popular cuts currently, however there are a great number of other popular choices such as the trilliant cut, asscher cut, carre cut, cushion cut, chess cut etc.