Our Pre-Auction Analysis focuses on elements that are hidden from the unprofessional eye. As always, we will describe the important visual elements for those who cannot attend the preview. The GIA report of each lot is available for everyone, thus we will discuss the visual characteristics that the report is silent about,  such as; Undertone, Color Dispersion, and Inner-Grade (UDI; a detailed explanation appears at the bottom of this article).

We use grades 1, 2, 3 and 4, 1 being the lowest grade. Grade 4+ is granted in rare cases and distinguishes stones with an exceptional characteristic. Stones that receive a minimum total UDI score of 8, without a remark, are considered to be “Gems” and are mostly suitable for high-end jewelry, collectors and the investment community.

For your convenience, we have added direct links for the GIA reports.


  • All images in this article review were taken with an iPhone 10, no filters were applied.
  • All auction valuations are per carat and in US Dollars.

Christie’s, Hong Kong Magnificent Jewels, November 27th 2018

Lot #2055

2.10 carat Fancy Vivid Blue round, brilliant cut, IF

High catalog estimation: $3,051,786 per carat

The rarity of this Fancy Color Diamond stems first and foremost from its hue, then its saturation and finally, its shape and size. According to the FCRF rarity data, a blue diamond that matches these characteristics is  unearthed once every 10 years approximately...