Our pre-auction analyses focus on visual elements that are not expressed in the GIA report, such as “inner-grade,” “undertone” and “color dispersion”. We use grades 1, 2, 3, 4 and 4+ to evaluate these features. Stones with a total score of 8 to 12, have the physical features of a Gem quality stone. It is often difficult to identify these characteristics when viewing stones in an auction catalogue. All pictures were taken with an iPhone 7.

Christie’s Lot No’ 216

9.14 Fancy Vivid Pink Pear shape VS2

High estimate: $1,970,000 per carat.

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According to our Rarity Evaluator, a stone with these gemological characteristics comes to the market once every few years and receives the “one of a kind” grade. However, rarity by itself is not enough in order for a stone to receive a high price per carat. The stone has good color dispersion with a moderate amount of colorless windows and receives an above average grade of 3. The inner-grade of the pear shape, which indicates the level of the intensity within each category, receives only the grade 2, which is below the average. The undertone is the most important attribute of pink fancy color diamonds. In the pink category the undertone ranges from warm (with an orange undertone) to cold (with a purple undertone). Pink diamonds with a presence of purple modifier (cold) are visually perceived to be more attractive and thus, this stone receives the grade of 4. This pear-shape receives a total score of 9.

 

Christie’s Lot No’ 155

10.30 carat Fancy Vivid Orangey-Yellow Emerald cut Internally Flawless.

High estimate: $290,000 per carat.

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The GIA report clearly describes this diamond as a Square Emerald cut. The auction catalogue, for some reason, describes this diamond as an Octagonal Step-cut. The stone has an exceptional inner-grade, and receives the rare grade of 4+, which is mostly seen in type 1b stones. The color dispersion is perfect for an Emerald cut and receives a grade of 4+. The stone’s undertone tends to be somewhat warm which is common with highly saturated yellow fancy color diamonds and receives the grade of 3. The caveat of this diamond is it has a high depth percentage and it looks a bit smaller than it actually is. The total score for this exceptional stone is 11++.

Sotheby’s Lot No’ 337

8.01 carat Fancy Vivid Blue Emerald cut VVS1.

High estimate: $3,120,000 per carat.

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Generally speaking, Emerald cut fancy color diamonds do not exhibit a high color dispersion. Due to the very wide corners near the culet this blue Emerald cut achieves a high color dispersion and receives a grade of 3. The undertone of natural blue diamonds, regardless of their intensity level, suffer from a significant gray influence. This Vivid Blue has quite a low amount of gray presence and receives a grade of 3, which is above the average for blue fancy color stones found in the market. The inner-grade is just below the mid-point on the Blue Vivid scale and receives a grade of 2. The total score for this unique diamond is 8.

Sotheby’s Lot No’ 336,

17.07 carat Fancy Intense Pink Emerald cut VVS1.

High estimate: $880,000 per carat.

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As seen in the picture below, this Fancy Intense Pink Emerald does not resemble the catalogue image. In contrast to the image, the stone has a strong (warm) orange undertone and receives a grade of 2. The color dispersion is quite low as well and is found only at the four narrow corners of the stone while the other large areas are quite dark, especially due to the steep angle of the pavilion. It receives a dispersion grade of 2. The inner-grade is above the average and receives the grade of 3. The total score of this stone is 7.