For many centuries, gemstone traders have been using certain terms to describe the outstanding colours of some specific gemstones. These “trade colour terms” are used for a particular type and appearance of gems, mainly describing a certain hue, but also implying other quality and rarity criteria, such as transparency, or the absence of treatments. Trade colours help the trade and the layperson even more, to distinguish the extraordinary and the rare.
Since its establishment exactly 100 years ago, the Gübelin Gem Lab observes the evolution of such trade colour terms. In 2005, it came up with a consistent and comprehensive definition and policy for the trade colour terms royal blue (for blue sapphires) and pigeon blood red (for rubies). Both terms were not limited to any particular provenance. However, the defined criteria for both royal blue and pigeon blood red were clearly based on the highest quality of blue sapphires and rubies originating from Burma (Myanmar). One property particularly characteristic of many Burmese rubies is a distinct fluorescence under both long- and shortwave UV-light. This fluorescent effect, often combined with a subtle presence of silk, creates the gentle glow inherent to pigeon blood red rubies.
Today, most rubies supplied to the world market come from places outside Burma, and hence lack this property. The Gübelin Gem Lab has decided to establish a new trade colour term for rubies displaying an ideal colour – identical to the colour of pigeon blood red rubies - combined with the best quality traits, while applying a different fluorescence criterion. The term Crimson Red was selected to accompany the best (rarest and most beautiful) rubies beyond fluorescence. Crimson describes a rich, saturated red colour, allowing also a minute admixture of purple.
In order to qualify for the Crimson Red colour call, first of all, the ruby must show the right hue, saturation and tone, evenly and homogeneously distributed across the stone. The stone must not show any major windowing or extinction. Furthermore, it needs to be spared from any treatment. Faceted stones must possess a cut producing a lively brilliance. Both faceted and polished stones can qualify, as can gems showing asterism, however, a high transparency is required. Crimson Red rubies must have little to no fluorescence in short-wave UV light (unlike pigeon blood red rubies).
Only the small share of high-quality untreated rubies, which fulfill all of these criteria qualify for the trade colour term “Crimson Red”.