The "girdle" is very much like a circumference that lies between the table (top) and the lower facets, as shown in the diagram above. The ideal girdle with appropriate proportions should be "medium". A great deal of Internet based companies sell diamonds with thick or medium to thick girdle. The problem with this from both a wow and quality factor is that by having a thick girdle you in effect have a much smaller (up to 20%) diamond.
A thick girdle on average can increase weight by 5%, and thus is often a trap that a less discerning diamond purchaser is unaware of. From a visual perspective it is much like comparing an ice cream cone and a muffin (from a bird’s eye view perspective). Although both diamonds are exactly the same weight, the diamond with a medium girdle is often around 20% larger in terms of circumference. Whereas the thick girdle diamond has more weight on the side and thus is smaller although higher (like a double scoop ice cream cone).
Furthermore the medium girdle (from a cutting formula perspective) allows perfect light refraction, and thus much greater sparkle and scintillation. The thick girdle loses and absorbs light, leading to a dramatically lower level of sparkle and scintillation. With this in mind Divinity Diamonds believes that diamonds with a medium girdle offer the best choice for the perfect jewellery piece.