The cut of a diamond is considered to be the most important attribute of the 4’cs. It has one of the most significant influences on the appearance of a diamond. How well a diamond is cut determines the amount of brilliance, fire and scintillation it possesses.
When talking about the effects of light in a diamond, brilliance refers to the amount of internal and external white light a diamond reflects. The more light that is reflected the brighter the stone will look. Fire is a result of light refracting around the diamond, causing white light to scatter into all the colours of the rainbow. Scintillation is the sparkle a diamond produces: white flashes of light and dark areas are caused by reflections within the diamond.
As shown in the images below the way a diamond is cut will have the greatest effect on how the stone interacts with the light. The light in a well cut diamond enters via the table, and then on to the pavilion where it reflects from one side to another before reflecting back out through the table of the stone. If the stone is cut too shallow the light leaks out of the bottom of the diamond, whereas if the stone is cut too deep it escapes out of the side. The less light reflected out of the top of the diamond to the eye the less brilliance the stone will have.
When looking at the proportions of a stone it is important to understand the anatomy of a diamond. An ideal cut stone is one that has a specific set of guidelines; this defines the proportions that give a diamond the optimum levels of fire and brilliance.
Polish and Symmetry
Other aspects that affect the cut of a diamond are polish and symmetry. After a diamond is cut the facets of the stone are polished. The level of polish is graded according to the finish left behind on the diamond’s surface. Symmetry refers to how well the diamond’s facets are aligned. A diamond is also graded on the levels of symmetry, assessing each facet for flaws such as being improperly aligned, irregular facets or an off-centre table
As the cut is so significant to a diamond’s final beauty and value, several grading systems have been developed. The most commonly used system today was created by GIA for the round brilliant cut diamond. To evaluate the cut grade of a diamond experts look closely at seven components. These include brightness, fire and scintillation which look closely at the diamonds overall face-up appearance. The other factors considered are weight ratio, durability, polish and symmetry which assess the craftsmanship and the design of the diamond.
The GIA’s diamond grading scale is pictured below
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