A diamonds beauty, rarity and price are all determined by the four Cs - Cut, Colour, Clarity and Carat weight. Diamonds with a combination of the highest 4C ratings are the most rare stones and will subsequently command a higher purchase price. No one C is more important than another in terms of the beauty and it is important to note that each of the 4Cs will not diminish in rating over time, and that no two diamonds are ever the same, each stone is completely unique.

Click any of the 4C titles below to read a more detailed description.


Cut is the only Diamond characteristic directly influenced by man - the others are dictated by nature. A good cut releases the fire and sparkle of a diamond through the arrangement and proportion of its facets.


Subtle colour differences allow gem quality diamonds to be graded from totally colourless stones through subtle hints of colour to the highly prized fancy colours.


Each diamond is graded according to its unique combination of inclusions - often called natures fingerprints. The fewer the number of inclusions, the rare the stone.

Carat weight

Carat weight is the method by which diamonds are sized. One carat equals 100 points, so the weight of a diamond of 25 points is 0.25 carats or 1/4 carat.


Refers to the angles and proportions of a diamond.

Cut is the human contribution to a diamonds beauty, brilliance and fire. The way a diamond is cut can affect all of the other Cs. Many people confuse "Cut" with the "Shape" of a diamond. The "Shape" refers to the outline of the stone and is more a choice of preference rather than a choice affecting quality.

A well cut diamond will reflect and disperse the maximum amount of light entering the top of the stone. This light will be reflected by the pavilion facets (back facets) and back out of the crown or top of the stone, resulting in a beautiful display of brilliance and fire. It is vital that throughout the long cutting process the scientific formulas for the proportion of the stone and angles of the facets are adhered to. Any deviation from the ideal measurements will result in a loss of brilliance and fire. If a stone is too deep or too shallow then some of the light entering the crown will leak through the side or back facets instead of being reflected back through the crown of the stone, leaving it displaying poor brilliance, which will be clearly evident when compared to another stone which has been cut to good proportions.

When cutting a diamond, the cutters have to choose between optimising weight or optimising beauty. Sadly, many cutters sacrifice beauty rather than weight. They can get away with this only because many suppliers have been keeping consumers in the dark and pushing weight rather than beautiful proportions. It is easier to convince someone to buy a bigger diamond than a more beautiful one. Most consumers have yet to understand that two diamonds with the exact same weight, colour and clarity can be purchased up to 40% cheaper if the cut is poor. This allows some jewellers to buy very poor makes and sell them in turn at prices reserved only for beautifully cut stones.

Diamonds can be cut to virtually any shape and size. Some popular diamond cuts include round, oval, marquise, pear, heart, emerald, princess and radiant. There is no doubt that round brilliant is the most popular cut today, which displays 57 facets (58 with a culet). Most brilliant cut diamonds cut before 1950 had the base of the pavilion cut off to form the culet. It was believed in the Victorian period that by doing this the stone would be more resilient, and less likely to break if it was to receive a blow, however as time went on and ideas changed with regards to the cutting of stones the culet became smaller and smaller until after 1950, the majority of brilliant cut diamonds nolonger display a culet.


The top section of the stone, divided into 33 facets

The rim of the stone, separatingthe crown (top) from the pavilion (bottom). This can be bruted (Rough), polished, or faceted.

The bottom section of the stone, divided into 24 facets (25 with culet)







Refers to the degree to which the diamond is colourless.

The determination of the precise colour of a diamond is the most difficult of the 4 Cs. Diamond colours range from icy white (sometimes described as of first water, meaning as pure as clear, limpid stream water), through to warm whites or yellow (sometimes described as by-water or bye). The colour of a diamond is graded using a colour scale established by the Gemmological Institute of America (GIA) which ranges from D (colourless) to Z (Yellow). The most desirable and valuable stones are the colourless D, to white H range. Stones graded below H will start to have a slight yellow tint, which will become more pronounced the further down the colour scale you go.



As the difference in colour is very subtle between neighbouring grades, diamonds are sorted into their colour grades under controlled lighting and conditions, with the use of master stones for comparison and accuracy.

Diamonds with a strong pure colour are known as fancy colour diamonds and can be found in a variety of colours to include - pink, blue, green, orange and yellow. These are very rare and command very high prices on the open market



Most of the diamonds that Offord & Sons sell fall into the F to H colour range, which produce beautifully white brilliant stones. Whilst higher colour grade diamonds are available, the naked eye is unable to detect the colour differences in these higher grades when mounted in jewellery, and so are usually used in specialty pieces or upon request.


Refers to the degree that the diamond is free of the naturally

Occurring inclusions, often called natures fingerprints. Most diamonds contain blemishes on the outside of the diamond or inclusions trapped inside the diamond.

In order to determine a diamonds clarity, many things have to be considered, such as - Size - How small or large is the inclusion ? Position - Where in the stone is the inclusion? Colour - How light or dark is the inclusion ? Number - How many inclusions are there in the diamond? Relief - How thick or thin is the inclusion? Nature - What type of inclusion is it? All clarity grading is carried out by an experienced professional with the aid of 10x magnification. Diamonds are placed into one of eleven grades ranging from Flawless (a completely clean stone free of any internal and external blemishes, and very rare) to I3 (a stone so full of inclusions that will possess very little beauty and will be much more prone to breakage). The fewer inclusions a diamond has, the rarer and therefore more expensive it will be

Most of the diamonds used by Offord & Sons fall into the ranges of VVS to SI, higher or lower grade diamonds are available upon request.

FL (Flawless) Completely clean and mark free
IF (Internally flawless) Clean internally, but slight external blemishes
VVS1, VVS2 (Very very slightly included) Inclusions, which are very hard to find under 10x magnification
VS1, VS2 (Very slightly included) Inclusions, which are hard to find under 10x magnification
SI1, SI2 (Slightly included) Inclusions, which are easy to find under 10x magnification, but not visible with the naked eye.
I1, I2, I3 (Included) Inclusions, which are visible with the naked eye.

Carat weight

Carat refers to the weight and therefore the size of a stone.

The carat weight is the most precise of the four Cs. The term carat is a derivative of the word carob, referring to the carob seed, which are very consistent in weight. Thus they where used in ancient times to measure the weight of diamonds, one carob seed equalled one carat. One carat equals 1/5 gram (200 milligrams) or approximately 0.007 ounces. Every carat is divided into 100 points. Therefore, a 50-point diamond is also called a ½ carat. Diamond weight is so precise that polished diamonds are weighed to a thousandth of a carat and then rounded off to the nearest hundredth (point). Diamonds weighing less than 20 points are often called melee. Another term often used is grain or grainer.

Loose stones are weighed directly on a scale, but mounted stones can only be estimated by putting their measurements into a mathematical equation. Since the price of diamonds is based upon rarity, assuming that colour, cut and clarity remain constant, the larger the stone the rarer the diamond and the higher the price per carat. A one-carat stone is much rarer than a half-carat stone, and is therefore will cost considerably more than double the price.


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