The 4C’s of buying a diamond

When you think about carat weight you should also think about millimetre size and diameters. The following diagram shows the approximate relative size of various carat weights in a round brilliant cut diamond that is cut to the same proportions. As you can see a 2.00ct diamond is not twice the diameter as a 1.00ct diamond, as previously explained.

Note: Use this chart as a relative guide only – actual size will vary with different monitor settings.

While most people assume diamonds are white, they can have traces of other colours. However, most people will struggle to see a difference in the colours of diamonds unless they are very yellow looking.

Colour grades are established by an experienced diamond grader comparing the diamond in question to a set of specially-graded master diamonds, under specific lighting conditions. The GIA colour grading scale is from D to Z and within this scale there are five broad categories: colourless, near colourless, faint colour, very light and light yellow.

Almost all diamonds have surface blemishes or internal imperfections called ‘inclusions’ by gemmologists.

Clarity grading involves identifying the different types of inclusions. These may not just the number of inclusions, but the size, and the position, for example, under the table, where they are more noticeable. Blemishes are the marks that appear on the surface. All these inclusions and blemishes can occur in both earth-mined, and lab-grown diamonds.

Naturally the fewer and less obvious are the inclusions and blemishes, the higher the clarity grade and the value. The GIA (Gemological Institute of America) grades diamonds on a Clarity Grading Scale ranging from Flawless (F) to Included (I3).

To be 100% sure that your diamond will be completely clean of eye-visible inclusions, choose diamonds graded VS2 or higher. At Adamastar we do not sell diamonds below SI2 clarity grade.

The cut of a diamond does not refer to the round or oval shape of a diamond. It only refers to the side on proportions of a round brilliant cut diamond where a skilled diamond cutter would use their knowledge and expertise to accurately shape the stone to maximise the diamond’s ‘fire and brilliance’. Of all the four C’s, cut is the one thing a diamond cutter has control over. A diamond that has been well cut, will appear very brilliant and fiery, but a poorly cut diamond will appear dark, or grey and lifeless regardless of how good its colour and clarity is.

The GIA Diamond Cut Grade only refers to Round Brilliant Cut diamonds and is graded in five grades: Excellent (EX), Very Good (VG), Good (G), Fair (F) and Poor (P).

Excellent diamonds are cut to perfect proportions, so they reflect and refract maximum light, producing the maximum fire and brilliance. Many of our diamonds are classed as 3x (or triple ex), cut grade – these being the diamonds that have been cut with superior craftsmanship to achieve a grade of Excellent in proportions, polish and symmetry.

Diamonds which are not round are all termed Fancy Cut Diamonds, and as such have a less critical criteria which is based on other factors such as how pleasing is the outline of the diamond to the eye, the symmetry, lack of ‘windowing’ and the proportion of depth to diameter.

An Ideal Cut Diamond is now called ‘Excellent’ by the GIA and refers to a round, brilliant cut diamond that is cut to ideal proportions, angles and can have excellent polish and symmetry ratings. An Excellent diamond is perfectly proportioned to refract maximum light, producing that fire and brilliance up through to the table and crown. Many of our diamonds are classed as 3x (or triple ex), Cut Grade, these being the diamonds that have been cut with superior craftsmanship to achieve a grade of Excellent in its proportion polish and symmetry. With lab grown diamonds there is little point in going to all the trouble of growing them and not cutting them to the highest standard.

When a diamond is seen from above with a special Hearts and Arrows viewer, the diamond displays a particular arrow pattern. When turned over and displayed from its pavilion side, the diamond presents the eye with 8 hearts with tiny ‘v’ shapes. Genuine Hearts and Arrows have these patterns visible at a single glance, indicating that the diamond has been cut with perfect optical symmetry and has perfect alignment between crown and pavillion facets.

Many of our diamonds display a true Hearts and Arrows pattern.

A well-cut diamond exhibits three different optical properties: brilliance, dispersion and scintillation . As light strikes a diamond’s polished surface at an angle, it will either reflect off a facet or the table or pass through and enter the diamond depending on the angle the light hits the facet. The light that is reflected off the diamond is known as the diamond’s brilliance. As light travels through a stone, some is reflected back, adding to the brilliance. Some of the light rays that enter the diamond is separated into flashes of colour as in a prism. This is known as dispersion. The result of dispersion i.e., the separation of white light into its spectral colours, is known as fire. Scintillation is flashes of colour that are viewable as an observer moves a diamond back and forth.

It is the technical mastering of these precise angles which maximise the three optical properties, which create the stunning visual effect of a round brilliant cut diamond.

Ideal Cut, now called ‘Excellent’

Diamonds cut with Excellent to Good proportions allow a maximum amount of light to be returned to the observer and thus have more brilliance and fire.

Too Deep

A diamond with a deep pavilion will appear dark in the centre of the diamond due to light leakage from the pavilion. Diamonds with a make grading of Fair to Poor will appear like this. Adamastar do not list diamonds with Fair or Poor make.

Too Shallow

A diamond which has a spread crown with a shallow pavilion is termed a ‘fisheye’ which shows as a white circle around the inside edge of the table when looking down on the diamond. This is actually the reflection of the girdle. Diamonds with this make are graded Fair to Poor will appear like this. Adamastar do not list diamonds with Good, Fair or Poor make. At Adamastar we only sell diamonds that have either an Excellent or Very Good cut grade.

As previously described, only ‘round’ diamonds have a ‘Cut’ grade. Fancy shapes have different criteria based on ‘pleasing to the eye’ proportions and other criteria.