The cutting of diamonds is an extremely complex and difficult art to master, and requires a deep and thorough understanding of shape and form.
Over the centuries that diamonds have been valued by humans as decorative items lapidaries (gem cutting professionals) and jewellers have fashioned and refashioned diamonds into a myriad of different varieties. You can read more about the different cuts here, but each cut has a variant of the sections described in the diagram above.
When modern diamonds are cut the craftsmen involved can use computer modelling and machinery to achieve angles and shapes that are as close as possible to absolutely perfect. Before the advent of this technology these processes had to be carried out by hand, meaning that simpler cuts with less facets were more common, but also meant that the more elaborate cuts represented hundreds of hours of painstaking work where any mistake could mean disaster.
The above illustration is representative of most diamonds, with the variations coming primarily through extending or shortening some of the lines and angles to create a particular optical effect. For example, cushion cut diamonds have a higher crown height than brilliant cuts, which leads to a greater crown angle and larger facets over the entire crown. These diamond cuts, which predate the electric light, are cut so as to take advantage of dimmer light sources such as candlelight.
When a lapidary or jeweller is assessing the quality of a diamond they take into account the symmetry and proportions of the cut. How closely the diamond adheres to, or diverges from, the standard of the cut it is intended to be dictates what kind of rating a professional appraiser will give, but there are other factors that must be considered.
A key aspect of a diamond’s finish is the polish that it has received at the last stage of its shaping. Even if every cut is perfect a substandard polish can severely affect the value of a stone.
The term ‘fire’ refers to the flashes of coloured light that occur when pure white light is split into its spectral components by the shape and form of the diamond. The diamond forms a number of prisms which divide the light into all of the colours of the rainbow.
This term refers to the light and dark areas that form within the diamond when it is viewed from above. Patches of shadow may serve to augment the inherent beauty of the brighter areas, or detract from them by dulling the stone as a whole. Assessing a diamond’s mathematical perfection is a scientific skill, but evaluating its fire and scintillation requires more of an aesthetic mindset, and can be thought of as closer to an art.
The Gemmological Institute of America (GIA) provides a scale for round brilliant cut diamonds that assesses them as being excellent, very good, good, fair or poor.
To read more about how we assess the quality of our diamonds take a look at our helpful Advice Centre.