GIA Cut Scale The 4Cs

As every diamond is different, a standard of grading them was introduced by the Gemological Institute of America (also referred to as GIA) as a way of comparing them. It allows consumers and the jewellery trade alike to help understand the different characteristics of a diamond. This grading is known as the 4Cs. Each of the 4Cs describes the diamonds characteristics – its carat, colour, clarity and cut.

These 4Cs give a diamond its unique personality and is what forms it basis for valuation. For example, a diamond would not be valued by carat weight alone – two diamonds of equal carat weight can have very different values depending on cut, clarity and colour.


The GIA Colour Scale extends from D (colourless) to Z (light yellow or brown).

Although many people think of gem quality diamonds as colourless, truly colourless diamonds are actually very rare. Most diamonds used in jewellery are nearly colourless with tints of yellow or brown.

Colour grades are determined by comparing each diamond to a master set. Each letter grade represents a range of colour and is a measure of how noticeable a colour is.

Fluorescence Some diamonds can emit a visible light when exposed to ultraviolet radiation, but fluorescence is not a factor in determining colour or clarity grades. However, a description of its strength and colour is provided on GIA Reports as an additional identifying characteristic.

Diamonds do also occur in shades of colour such as yellow, pink, blue, green and red. These are graded separately according to their intensity of colour. This stones are known are ‘fancy diamonds’ and are extremely rare and valuable.


The GIA Clarity Scale includes eleven clarity grades ranging from Flawless to I3.

The clarity of a diamond refers to the presence of inclusions with the diamond. These natural inclusions in the stone form the diamonds individual fingerprint. So the clarity grading measures the diamonds purity. A gemologist will look at the diamond through 10x magnification before giving it a clarity grade ranging from F (flawless) to I (included).

Inclusions within the diamond can influence the way the light is reflected. Flawless stones are rare; most diamonds will show small inclusions although many are invisible to the naked eye.

      Because diamonds form under tremendous heat and pressure, it is extremely rare to find a diamond that lacks any internal and external characteristics. These characteristics are a by- product of its formation and help gemologists separate natural diamonds from synthetics and simulants, and identify individual stones.


The GIA Cut Scale ranges from Excellent  to Poor.

It is the only one of the 4Cs that is influenced by man.

A polished diamond’s beauty lies in its complex relationship with light: how light strikes the surface, how much enters the diamond, and how, and in what form light returns to your eye.

The result is a magnificent display of three attributes. Brightness is the combination of all white light reflecting from the surface and interior of a diamond. Fire describes the “flares” of colour emitted from a diamond. Scintillation describes the flashes of  light you see when the diamond, the light, or the observer moves.

A polished diamond’s proportions affect its light performance, which in turn affects its beauty and overall appeal. Diamonds with fine proportions, symmetry, and polish optimise their interaction with light, and have increased brightness, fire, and scintillation.

The cut shouldn’t be confused with the shape of the stone.

GIA Colour Scale GIA Clairty Scale GIA Diamond


The carat is a measure of weight, not size. To accurately measure the carat weight of a diamond it should a weighed as a loose stone before setting.

The measurement of one carat (1ct) is equal to 0.20 grams and can also be divided into points – 100 points equals one carat. Therefore a half carat diamond is 50 points (0.50ct).

GIA Carat Weight

The 5th C

Sometimes there is a 5th C that is referred to. This can be a variety of ‘Cs’, sometimes Country of origin, Certification or maybe more importantly - Confidence in your jeweller.

Beauty and Its Beholder

The 4Cs provide a way to objectively compare and evaluate diamonds, but numbers alone can’t describe a diamond’s mysterious and captivating beauty – for that, you’ll have to visit your local jeweller to see one for yourself.


Quality Jewellery in Canterbury


Anthony W Pearce


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