This Sotheby’s Hong Kong pre-auction analysis focuses on visual elements that are not expressed on the GIA report, such as Undertone, Color Dispersion, and Inner-Grade (UDI). We use grades such as 1, 2, 3, and 4 to describe these features. The grade 4+ is used in special cases to describe unusual visual characteristics. Stones with a total score that ranges from 8 to 12 are considered top gems and are suitable for high jewelry. It is often difficult to identify these characteristics when viewing fancy color diamonds only in an auction catalogue, especially when the images are heavily processed. All images in this review were taken with an iPhone 7.

Important note: To all you auction bidders; we strongly recommend downloading the beta version of the new FCRF app and using the auction calculator. The app lets you calculate your bidding price per carat (including the house commission) as you follow the lot, and create your own archive.

Lot No’ 1784

3.13 carat fancy intense blue emerald cut. High catalogue estimation: US$: $1,640,000pc

As the Cullinan mine produces only a very small amount of blue fancy color diamonds every year, any natural blue that comes into the market creates a lot of interest, especially in the intense grade.

The color inner-grade receives a 3, which means it is a solid “intense.” Generally speaking, due to the unique facet alignment and angles of an emerald cut stone, the color dispersion for this shape is very challenging. This stone receives the relatively high grade of 3 as well. The undertone in a blue fancy colored diamond is measured by the quantity of gray in the color mix. In this particular case, the stone introduces a clear blue undertone with very little gray influence and receives the grade 4. We suggest buyers note the very large crown and the very small table (54%), which is not very common in emerald cut   diamonds. Total UDI score: 10

Lot No’ 1732

8.00 carat fancy vivid yellow heart shape. High catalogue estimation: US$96,000pc

As seen in our image below, this vivid yellow heart shape diamond has quite impressive visual qualities. Its inner-grade receives the relatively high grade of 3 and a color dispersion grade of 4. In order to receive a high grade for the undertone, a yellow diamond needs to stay as close as possible to a primary yellow, which is the pure form of yellow. This vivid heart has very little brown or green influences and thus receives the grade of 4 for the undertone. The two significant caveats of this stone are the facts that the stone is exactly 8.00 carats, and that the general rounded shape towards the point and small shoulders of the diamond doesn’t really correspond to the classic heart shape model. Total UDI score: 11

Lot No’ 1696

11.44 carat fancy orangey pink radiant cut. High catalogue estimation: US$280,000pc

Large fancy color diamonds that carry a pink hue in their mix are rare. However, in this case, the visual attributes of this stone are relatively low. The stone has a large colorless crown and a small table (58%) and receives the grade 2 for color dispersion. The inner-grade is quite low as well and only receives the grade 2. Very few fancy color diamonds with a combination of pink and orange have an attractive ‘peachy’ hue. Most of them, and this stone in particular, can easily be mistaken to look like a brownish pink. Although the catalogue image portrays the diamond completely differently, the stone receives the grade 2 as well.

Total UDI score: 6