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Commins & Co Jewellers, Powerscourt Townhouse Centre, 59 William St. S, Dublin 2. Tel: 01-4422472.   Google Places (100 reviews)

The Four C’s of Diamonds (& Fluorescence)

When the quality of a diamond is assessed, the 4 Cs are the determining factors: Colour, Cut, Clarity and Carat weight. Another key characteristic of diamonds is Fluorescence which will also be discussed. Let’s explore what makes a high-quality diamond, and what does not.

1. Diamond Cut

  • There are various types of cut for diamonds. As a result, the quality of a cut determines the stone’s proportions that define its scintillation; its level of sparkle.
  • There are many facets and angles that play a role in the quality of a diamond’s cut.
  • When it’s done right, the cut will allow light to pass through the diamond in the right way. This allows the light be reflected back to the viewer’s eye.
  • A poorly cut diamond will leak the light, resulting in less light being reflected and less sparkle.
  • When you look closely at a diamond to examine the cut,you can see the difference between an Ideal/Excellent cut and an inferior Fair cut grade.
  • The proportions of a superior cut will result in excellent symmetry and a lot of sparkle. An inferior one will appear less lively and sparkle considerably less.
  • The angle of the pavilion also plays a key role. If it is too deep or shallow then it won’t reflect a lot of light back at the viewer.
  • As you move down the scale, you lose much of those essential properties. As a result, a Fair or Poor cut is dull and lifeless – in short, they are bad value for money.


2. Diamond Clarity

  • Since they are formed very deep underground, subjected to extremes of heat and pressure, most diamonds contain some kind of ‘birthmark’.
  • Many of these cannot be seen with the naked eye.
  • These appear in the form of tiny imperfections inside, which we call inclusions. If they are on the surface, we call them blemishes.
  • A diamond’s clarity, therefore, refers to the degree to which such imperfections exist on/in a stone.
  • Diamonds with multiple or significant blemishes and/or inclusions have inferior brilliance. This is because those flaws obstruct the path of light moving through the stone.
  • There is a diamond clarity scale that classifies stones on the basis of how much any existing imperfections affect a stone’s performance.
  • At the top of the scale, there is the flawless (FL) diamond. This means absolutely no inclusions or blemishes can be found even by the most skilled grader under 10x magnification. These are incredibly rare – fewer than 1 in 5,000 diamonds qualify for an FL rating.
  • We don’t recommend going any lower than Sl2 on the clarity scale. We specialise in eye-clean Sl2.
  • This means stones that have low-grade flaws that are not visible to the naked eye.
  • For every 50-100 Sl2 stones we examine, we may only accept 1-2.  We emphasise the highest standards in our stones, and clarity is one of the key factors in ensuring a diamond performs well.
  • In grading diamond clarity, we consider the number, colour, size, positions and reflectivity of every visible flaw under magnification.

In summary, the fewer the inclusions on the diamond, the more valuable the diamond.

diamond clarity

3. Diamond Carat

  • The carat-weight of a diamond measures the weight of a diamond and not the actual “size”: 1ct = 0.2 gram
  • With all other factors equal, the larger the diamond’s carat weight, the higher the price as a larger diamond is usually preferred.
  • However, two diamond of equal carat weight but large differences in cut, clarity, etc, can have a major price differential
    (Note: Images not to scale, pictures shown are for comparison purposes only).


diamond carat

4. Diamond Colour

  • The closer a diamond is to being colourless, the rarer and more valuable the stone.
  • Subtle differences in colour can have a significant impact on the quality and value of a diamond.
  • Though two diamonds may be matched in clarity, weight and cut, if there is a colour difference then they are not a match in terms of their overall value.
  • Rarity is the determining factor that influences a stone’s value with regards to colour, which is why subtle variations can make a big difference.
  • It is important to have an accurate assessment made of a stone’s colour in order to establish its rarity beyond all doubt.
  • There are various colours that diamonds can come in, as you will have seen from the vast range that exists.
  • Diamonds can be measured on a colour scale which ranges from D (the best and colourless) to Z (light yellow).
  • The normal range is between colourless light down to a noticeable yellow or brown hue. When tested under the correct conditions, this yellow ray is very noticeable.
  • When grading diamonds, testers must analyse the stones under controlled laboratory conditions, comparing them to masterstones.
  • Colour must be established as precisely as possible in order to provide an accurate valuation of a diamond.

Diamonds that are high up the colour grading scale, such as D, E, & F, are considered to be most valuable.


diamond colour scale


(+1) 5. Fluorescence

Although fluorescence is not part of the fundamental 4 Cs, we deem it of crucial importance when choosing your diamond.

  • Many diamonds give off a visible light called fluorescence when ultraviolet (UV) radiation is directed at them.
  • Under the right conditions, you can see the fluorescence emitted by a diamond, and as many as 35% of them do it.
  • The most common fluorescent colour in a diamond is blue, but it can also be yellow, white, orange and various other colours.
  • You need to understand that fluorescence devalues a stone, despite many in the industry using it as a selling point.
  • Just like how a poor cut can result in a higher carat weight, enabling certain sellers to value a stone higher than one with a superior cut, a stone with high fluorescence is sometimes sold as though this is a desirable property.
  • At Commins & Co. we only sell diamonds with NIL fluorescence, and we’ll tell you why:
    Fluorescence masks the true colour of a diamond. If a lower-grade yellow stone has strong blue fluorescence, the yellow colouring it has will often appear closer to colourless in sunlight. This is because blue and yellow are actually colour opposites, meaning that they effectively cancel each other out – the blue fluorescence masks the yellow colour.
  • Furthermore, if fluorescence is particularly strong it can give a stone a slightly cloudy or ‘oily’ appearance.
  • This, in itself, will lower the value of a diamond, regardless of whether it has that misleading effect on assessing the stone’s colour.
  • In short, fluorescence is something to be avoided, and this is why we never sell diamonds with anything but NIL fluorescence.

Image result for fluorescence diamonds



When viewing engagement rings or diamond rings, please ask your jeweller to explain the 4C’s to you as well as Fluorescence. This will ensure that you are getting the best price and quality of your diamond.


Availability and Convenience

Availability and Convenience

Open 7 days a week, Monday to Saturday. No appointment necessary and located 1 minute walk from Grafton Street.
Customer Service

Customer Service

Free sonic cleaning with all rings along with having a in house goldsmith available for all amendments.


Up to 50% below high street prices due to our network with diamond dealers and low overheads.
Free independent valuation

Free independent valuation

All our diamond rings come with free independent valuations worth over €100 from Irelands leading gemmologist.


Over 800 diamond rings in stock – all available to be amended to suit your style and budget. Access to over 1 million certified diamonds.