Cutting is an important category among the 4C rating. When purchasing round diamonds, you could pay attention to the diamond’s certificate and see if its cutting is of “Ideal” or “Excellent” rating as it plays a key role in affecting the brilliance of your jewelry. Even if the diamonds are of the same shape, their spark could vary greatly. Then how do those appraisal institutes judge the cutting?
Take IGI as an example, cutting could be further divided into three sub-categories: cut ratio, polishing and symmetry.
Cut ratio includes the overall ratio, size and angle of the cutting plane. IGI would use the data to compare the spark, brightness and shape for analysis. Diamond’s parameters such as the height and angle of the diamond’s pavilion and crown, the ratio of the diamond surface, the width of the diamond’s girdle and the overall depth of the diamond are numbers IGI needs to evaluate before it makes the decision on the rating.
The standard for IGI’s rating is very strict. Other than the common “Excellent” rating, they also have the “Ideal” rating. A diamond can be deemed “Ideal” only when its parameter(other than the ratio of its surface) is within 3% difference of IGI’s standard.
Polishing and symmetry are relatively less important when it comes to the overall shine of a diamond. IGI would judge the smoothness of the diamond, the trace of it being polished and the alignment of its facets and edges. The trace of polishing is difficult to see with naked eyes and the quality of polishing would only affect the shine of a diamond, so its effect on the overall spark and brilliance is negligible.
The above mentioned ratios are important factors in affecting a diamond’s spark and how the light reflects within it. The size and angle of diamond’s facets would alter the path of light exiting the diamond.The brilliance of a diamond would be the most dazzling when every streak of ray could be presented from the inside to the outside at precise angles.