The diamond guide

The 4Cs

Cut, colour, clarity and carat weight are the four characteristics a grading laboratory records for every diamond. The system was developed by the Gemological Institute of America (GIA) in the mid-twentieth century, and its scales are now the common language of the diamond trade. No single C makes a diamond beautiful: it is the balance between them, and the shape you love, that decides which stone is right for you.

Cut

Cut describes how well a diamond’s facets are proportioned, aligned and finished, and so how it handles light. A well-cut diamond returns light to the eye as brightness, scatters it as flashes of colour (fire) and shows a lively pattern of light and dark as it moves (scintillation). A poorly proportioned stone leaks light through the bottom or sides and looks darker or glassy, whatever its colour and clarity.

For round brilliants, GIA gives an overall cut grade on a five-step scale: Excellent, Very Good, Good, Fair and Poor. The grade takes into account the stone’s proportions (table size, crown and pavilion angles, girdle thickness) as well as its polish and symmetry. Polish and symmetry are also graded on their own, on the same Excellent to Poor scale.

Fancy shapes (every shape other than round) do not receive an overall cut grade from GIA, because what looks best varies from shape to shape. For these, look at the polish and symmetry grades, the depth and table percentages, the length-to-width ratio and, above all, the photographs and video of the stone itself.

How to use it: for a round diamond, an Excellent cut is the safest choice for maximum sparkle, and it often lets you choose a slightly lower colour or clarity without a visible difference. The diamond search lets you filter by cut, polish and symmetry.

Colour

Colour grading measures the absence of colour in a white diamond. GIA grades colour on a scale from D to Z, comparing each stone face-down against master stones under controlled light:

• D, E, F: colourless. The rarest grades. Differences between them are visible only to a trained grader side by side.
• G, H, I, J: near colourless. They look colourless face-up to most people once set, especially G and H.
• K, L, M: faint colour. A gentle warmth that can be lovely in yellow or rose gold.
• N to R: very light colour, and S to Z: light colour. Visibly tinted, usually yellow or brown.

Yellow or brown diamonds deeper in colour than Z, and diamonds of other colours such as pink or blue, are graded on a separate fancy-colour scale.

How to use it: the setting changes how colour reads. White gold shows the whitest look and suits D to H; yellow and rose gold flatter warmer stones, so a near colourless I or J can look beautifully bright in them. Larger diamonds and step cuts (emerald and Asscher) show colour a little more readily than brilliant cuts.

Fluorescence is listed on the report too: how the diamond glows under ultraviolet light, from None through Faint, Medium and Strong to Very Strong. Most is invisible in daylight; strong blue fluorescence can occasionally make a stone look slightly hazy, so we show it on every diamond page.

Clarity

Almost every natural diamond contains tiny features formed as it grew: inclusions inside the stone and blemishes on its surface. Clarity grades how many there are, how large, where they sit and how visible they are, judged under 10× magnification. GIA uses eleven grades:

• FL (Flawless): no inclusions or blemishes visible under 10× magnification.
• IF (Internally Flawless): no inclusions, only minor surface blemishes.
• VVS1 and VVS2 (Very, Very Slightly Included): inclusions very difficult for a skilled grader to see at 10×.
• VS1 and VS2 (Very Slightly Included): minor inclusions, difficult to see at 10×.
• SI1 and SI2 (Slightly Included): inclusions noticeable at 10×.
• I1, I2 and I3 (Included): obvious inclusions that may affect transparency and brilliance.

How to use it: most people look for an “eye-clean” diamond, one with no inclusion visible without magnification at a normal viewing distance. VS diamonds are almost always eye-clean, and many SI1 stones are too. Brilliant cuts (round, oval, cushion, pear, radiant, princess, marquise, heart) hide small inclusions well; step cuts, with their open, mirror-like facets, show them more readily, so a VS2 or better is worth considering for an emerald or Asscher. Where it matters, check the photograph and video of the stone.

Carat

Carat is a unit of weight: one carat is 0.2 grams, divided into 100 points, so a 0.75 ct diamond is “75 points”. It is not a measure of size. Two diamonds of the same weight can look different in size face-up depending on their shape and how deeply they are cut. As a guide, a well-cut one-carat round diamond measures about 6.5 mm across.

Larger diamonds are rarer, so price rises faster than weight: a two-carat diamond costs considerably more than two one-carat diamonds of the same quality. Prices also tend to step up at popular weights such as 0.50, 0.70, 1.00 and 1.50 ct.

How to use it: elongated shapes such as oval, pear and marquise face up larger than a round of the same weight. A diamond just below a popular weight (for example 0.90 to 0.99 ct) can look almost identical to one at the round number. Every diamond page shows the stone’s measurements in millimetres, and the on-hand view shows it at true size.

Shape

Shape is the outline of the diamond seen from above, and the most personal of all the choices. The round brilliant is cut to return the most light; every other shape is known as a fancy shape, each with its own character and ideal proportions. We offer round, oval, cushion, pear, emerald, radiant, princess, marquise, asscher and heart diamonds. A guide to diamond shapes explains how each one handles light and which settings suit it.

Grading reports

Every diamond we offer is graded by an independent laboratory, and the laboratory is named on its certificate, together with the report number supplied with the stone. The report records the stone’s shape, measurements, carat weight, colour, clarity and, for round brilliants, cut grade, as well as polish, symmetry and fluorescence. Where a report link is available, we show it on the diamond’s page so you can check it yourself, and the report comes with your order.

The Gemological Institute of America (GIA), a non-profit institute founded in 1931, developed the 4Cs and its reports are widely used as a reference; you can check any GIA report number on its Report Check service. The International Gemological Institute (IGI), founded in Antwerp in 1975, is one of the largest grading laboratories in the world. Browse GIA graded diamonds or IGI graded diamonds, or read Diamond grading reports explained.

Natural diamonds

All Lavandela centre diamonds are natural, mined diamonds sourced from live trade inventory. Each one is unique; once reserved, it is no longer available to anyone else.

Putting it together

Start with the shape you love and a budget, then decide which C matters most to you. If sparkle comes first, choose the best cut you can and relax colour and clarity a little. If size comes first, an elongated shape, a near colourless colour and an eye-clean SI or VS clarity give the most diamond for the budget. If you want a stone that is close to perfect, keep the cut excellent and move up in colour and clarity before carat. The diamond search has three starting points for exactly this: most sparkle, best balance and best value.

Then the setting: our guides on choosing an engagement ring setting and 18K gold cover the rest, and how our prices are built explains what you pay for. Choosing earrings? Read how we match a pair of diamonds.

Choosing your gold

We work only in solid 18K gold: yellow, white and rose. You can switch between them on any setting and see the change live.