Diamonds the 4Cs

Information on Diamonds

Diamonds throughout history have always been admired and feared, so it is not surprising that they have found their way into the centre piece of traditional engagement rings representing prosperity, love and spirituality.

When choosing how much to spend on the diamond of your engagement ring, its important to remember that a stone's value is set by its quality and not just by its size. The universally agreed measures, known as the 4C's - cut, clarity, colour and carat, will fairly accurately define a diamond's quality. Having said that, it is important to remember that every diamond is unique and you need to see the stone you are buying, accompanied by an expert, to be sure you are buying the best diamond for your money, regardless of whether the stone comes with a certificate or not.


Not to be confused with a precious metal's carat (eg 9 carat or Karat gold in America), this refers to a stone's weight and, as all diamonds are the same density, its size. A carat equals 0.2 grams and this can be divided into 100 points. The term originated in ancient times where each diamond was weighed by comparison with a carob bean - a rather inaccurate measurement and many dealers had 'sellers' and 'buyers' beans! Nowadays we use very accurate electronic scales.

It is worth remembering that several smaller stones added together to total 1ct will not equal the value of a single 1ct stone, even of the same quality. This is because the larger the stone the rarer it is.

View our carat to millimetre chart to get an approximate indication of how big a diamond will look.


With non-fancy diamonds (ie white ones!) a universally accepted scale exists (defined by the Gemmological Institute of America). The scale is divided into steps between "D" and "Z" - D being the best (or whitest).

  • D - E exceptional white
  • F - G rare white
  • H white
  • I - J slightly tinted white
  • K - L tinted white
  • M - Z tinted colour

Upwards of “G" colour and the price escalates dramatically as the rarity increases, so for a certain budget the size of the stone would be compromised. We pride ourselves in choosing the perfect stone for each customer based on their preferences and budget.

Natural coloured diamonds, or 'fancies', are rare and valuable - blue, green, pink and yellow occur as well as the wonderfully rich 'black' or 'cognac' stones. Naturally occurring coloured diamonds are very valuable - for example a naturally occurring red or pink diamond can cost the same as a house! Brand new technology means that diamonds can now be heat treated using very high temperatures and pressures to produce colour changes. The technique produces intense aqua blues, greens, blacks, yellows and golds. These heat treated diamonds are generally more costly than white diamonds but are affordable. The exception to this is that naturally occurring cognac diamonds are affordable and we tend to use these in our engagement rings. In general terms, the less brown or grey present in a coloured stone and the more evenly saturated the colour, the higher the price.

Only a small percentage of diamonds can be successfully colour improved using artificial methods and it is important that a treated diamond must never be heated by a jeweller in the future (e.g the treated diamonds must always be removed and then reset with a resize). The reheating can result in the enhanced colour either changing or being lost. In case of particular sensitivity to heat, it is also not advisable for them to go through a rhodium plating process or be ultrasonically cleaned.


The grading system (or Cibjo Clarity Scale) refers to the amount of inclusions in a stone when viewed through a 10X magnifying lens (or loupe).

  • IF (loupe clean) - absolutely free from inclusions.
  • VVS (1 and 2) - very very small inclusions, virtually invisible through a 10X loupe.
  • VS (1 and 2) - very small inclusions, hardly visible through a 10X loupe.
  • SI (1 and 2) - small inclusions visible through a 10X loupe but invisible to the naked eye.
  • P1 - inclusions immediately evident with a loupe though hard to see with the naked eye.
  • P2 - large/numerous inclusions visible to the naked eye and affecting brilliance.
  • P3 - large/numerous inclusions very visible to the naked eye and affecting brilliance.

When choosing a diamond, there is a trade off between size and quality but we will always talk to our customers about the perfect stone for them. It is worth remembering that this scale is a scientific tool to enable dealers to communicate effectively and that a diamond is a unique piece of nature of which inclusions are a part and may not affect its beauty.


This craft began in Bruges in 1476 and is a time consuming and complex job involving splitting the uncut diamond into smaller fractions - the skill is to utilise the best faces and end up with a stone where the light is reflected out as effectively as possible. A badly cut stone will look dull and lack the 'fire' of a well cut stone. A common misunderstanding is that stones set completely within a shank (ie with no light entering the stones from the side) will appear less bright. This is not true with well proportioned brilliant cut round stones, as a well cut diamond is engineered for 'total internal reflection' - ie what goes in the top comes out again from the top!

Diamond cuts are sometimes given a grading such as 'ideal'. At Harriet Kelsall Bespoke Jewellery we would only consider using diamonds that meet this standard of cut.

Cut styles are changing all the time as new ones are being invented (eg princess cut) and old ones are losing popularity (eg rose cut).

Harriet Kelsall Bespoke Jewellery has built up a network of diamond dealers that guarantee that any stone sourced for your engagement ring will be of the finest possible quality and value for money. We are particularly keen to ensure that all the stones that we use are conflict free - ie have not been sold to fund terrorism. Together with the British Jeweller's Association and the Responsible Jewellery Council, we are working to eliminate these stones from the market completely.

If you would like more information or to arrange a design consultation please contact us.