Diamond Guide

The information below was written by our gemologist as a straight forward guide to the factors that influence the value of diamonds. By analysing the four key factors: carat weight, cut, clarity and colour and answering often asked questions we believe this guide will provide an invaluable asset in selecting your next diamond from Walker & Hall.

Introduction

Diamonds are essentially pure carbon which has been forced to crystallise under intense pressure and very high temperatures into a unique crystal structure.

The age old attraction of the diamond is that due to its incredible hardness it works as a visual dynamo reflecting and refracting light.

Essentially a diamond sparkles. It acts as both a mirror, reflecting white light and as a prism, breaking up (refracting) light into the spectral colours.

The value of a diamond can therefore be easily understood in terms of its ability to sparkle - its brilliance, its fire, its life.

Carat Weight

The term carat weight originates from the historical unit of measuring precious gems, the carob seed. The term is now standardised to represent .02 of a gram and a carat is further broken down into 100 points, thus 25 points is equivalent to 1/4 of a carat.

Carat weight is the factor that most affects the value of a diamond simply because larger diamonds in their natural state are so much rarer than smaller ones.

Cut

Cut is the only quality variable directly affected by man. It applies not only to the overall shape of a diamond but also to its polish, symmetry of facets and, most importantly, to the various angles and proportions of the diamond.

The most popular shape of diamond is the round brilliant. This is due to its perfect symmetry and resulting evenness of sparkle. Other brilliant cut shapes such as the pear, marquise, oval, heart and square are asymmetrical and as such have concentrations of sparkle. The other type of cut is the step cut where the facet shape is rectangular, as opposed to triangular. Emerald and baguette cut diamonds are popular examples of the step cut.

GIA Cut Grading Scale Excellent - Very Good - Good - Fair - Poor

The proportions to which the diamond is cut is essential in unleashing its optical wizardry. Key factors are the pavilion depth and crown angle. If a diamond is cut either too deep or too shallow light will be lost, thus reducing the sparkle, and value, of the stone.

The Passage of Light Through Diamonds

	Diamond cut too shallow Light lost through crown.
	Diamond cut too deep Light lost through pavilion.
	Perfect cut (A) shows the external reflection of white light. (B1) shows the internal reflection of white light. (B2) shows the refraction of white light.

Clarity

Due to the rigorous nature of formation almost all diamonds contain inclusions which vary so that no two stones are identical.

The category into which a diamond is graded with regards clarity is determined by the size, nature, position, relief and number of inclusions.

Diamond clarity grades range from flawless (Fl) to heavily included. Between these ends of the spectrum are very very small inclusions (VVS), very small inclusions (VS), small inclusions (SI) and included (I) grades.

GIA Clarity Grading Scale Fl - VVS1-2 - VS1-2 - SI1 - SI2 - I1 - I2 - I3

A key distinction in clarity grading is between diamonds in which inclusions can be seen with the eye and diamonds with inclusions that cannot. This is generally between the SI2 and the I1 grades. Diamonds graded I1 or below have inclusions visible to the eye, this detracts from the attractiveness of the diamond and can also affect how light passes through the stone reducing it’s sparkle and value.

Conversely, diamonds graded above SI1 will not necessarily, when mounted, appear any more brilliant than SI1 clarity stones. Value above this grade is therefore often related more to rarity than beauty.

Colour

It is not colour but an absence of colour which is most desirable in a diamond. A colourless diamond provides a pure background which intensifies the flashes of fire.

Colour, in the vast majority of diamonds, comes in shades of yellow or brown and is caused by nitrogen impurities in the diamond's atomic structure.

Colour grading has historically incorporated a many different scales but has now, through GIA, been standardised into an internationally accepted system. The alphabetically based system starts at D, colourless, and moves downwards to Z, heavily tinted.

Unlike clarity, where differences are not always apparent to the naked eye, one can always detect differences in colour. It is for this reason that many people choose to select a higher colour diamond over one of higher clarity.

GIA Colour Grading Scale
	D E F Fine White		G H I White		J K L Slightly Tinted		M N Z Tinted

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