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Diamond Guide

Cut: ‘Cut’ is used to describe two qualities of diamonds. The ‘cut’ of a gemstone – in this case diamond – predominantly refers to the shape and style of the facet arrangements. For example, the most popular and scintillating cut is the well-known round brilliant cut. This is an arrangement of 57 or 58 facets, depending on if a culet is present or not, with a “brilliant” pavilion. This arrangement of facets is seen on all “brilliant” cut diamonds, which can be: heart, pear, marquise, square modified (more commonly known as “princess cut”), cushion, radiant or oval. There are other styles of ‘cut’ including the stunning emerald cut and asscher cut, which have stepped pavilions and non-standard fancy cuts that are most often designed by high street brands.

The other use for the term ‘cut’ is when describing part of cut, polish and symmetry. This will be explained in further detail under Cut, Polish, Symmetry.

Colour: Diamonds are graded in an order of whiteness, using the scale D – Z. ‘D’ is the whitest, with absolutely no draw of colour under 10x magnification. ‘Z’ contains the most draw of colour without the diamond being termed “Fancy”. Most commonly the draw of colour is yellow, but it can also be grey or brown. Anything above the colour “I” is considered white to the naked eye. At this level, it is more a perceivable warmth to the white of the diamond, much like paint colours which are described as “absolute white” “pure white” and “brilliant white” – all white of varying degrees. All diamonds which have been graded by professional grading laboratories are compared to what is known as a “master set” of diamonds. These have been graded by leading laboratories to be at the top of their assigned grade. The diamond to be graded is compared against the “master diamond”. Starting from the lower end of the spectrum moving upwards, the diamond to be graded is compared to the “master”. When the diamond is no longer whiter than the “master diamond”, the diamond is assigned that colour grade. When certified by a genuine and respected laboratory, all of this will have been performed in ideal conditions, using 10x magnification, daylight lamps, a minimum of two qualified graders with a third to adjudicate and in an area where no outside colours can affect the grade. At The Jewellers, we only use the best certificates for our diamonds. We consider these to be GIA, IGI, HRD and AnchorCert. When grading our own diamonds, we adhere to GIA (Gemological Institute of America) guidelines and nomenclature.

NB: If a diamond is mounted/set before certifying, then it is considered to be “assessed” and not “graded” as grading can only be accurate when the diamond is loose.

Clarity: Causing more disagreements in the world of diamonds than any other attribute, ‘clarity’ describes how much effect natural inclusions are having on the stone. There are six characteristics which determine an overall clarity grade: position, colour, nature, size, number and relief. The universally accepted scale follows the GIA which is described below:

All clarity grading is assessed under 10x magnification, without the use of a microscope. Any grade above “SI2” (slightly included 2) is considered to be ‘clean to the naked eye’ – meaning that the wearer should not see any blemishes with the eye alone.

NB: The grade “SI3” is not acknowledged nor accepted on the diamond market and should you come across a certificate with this grade, be assured it is not from a globally respected grading laboratory.

Carat: One of the most important points to many, the ‘carat’ describes the weight of a gemstone. Most think carat is the size of the gem but although it is a contribution, the size like many things, is all about weight distribution. To put ‘carat’ in to perspective: 1.00ct = 0.20gram / 5.00ct = 1.00gram. You may hear carats described slightly differently between dealers. A 1.00ct is also known as 100 points; a half carat/0.50ct as 50 points; a quarter carat/0.25ct as 25 points and so on.

Cut, Polish, Symmetry: An unknown factor by many, these three grades often have more effect on both appearance and price than the 4C’s put together.

Describing three separate properties, each is individually graded on a scale of poor, fair, good, very good or excellent.

Cut in this instance, describes the quality and shape of the diamond. For each cut style there are optimum angles and percentages that equal different qualities of cut. To assess these accurately, the diamond is placed on a machine called “Sarin”, which assesses all the angles through a 360° video feed. Using specialist software written especially for the purpose, the cut grade will be assigned.

Polish is used to describe the overall finished quality of the diamonds polish. The amount of graining, residual polishing lines or abrasion and any burnt facets affect this grade.

Symmetry is used to grade: how ‘round’ (or well-shaped) the diamond is; how accurately the facet edges meet up; how central the culet is to the table; how well the table is centred and how level the table is.

Fluorescence: An amazing phenomenon affecting approximately 30% of diamonds, due to varying chemical elements within the structure. Describing the diamonds reaction to ultraviolet (UV) rays (which is a component of daylight) and the intensity of the visible light that is emitted when exposed to it.  Many people believe that fluorescence is detrimental to the overall quality of the diamond, but mostly it is quite the opposite and when appreciated, it is a beautiful and fascinating effect.


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