SSEF, Gubelin agree on gem color standards

Basel, Switzerland--Swiss labs Gemmological Institute SSEF and Gübelin Gem Lab have harmonized their standards of color and quality criteria when it comes to the terms “pigeon blood red” and “royal blue,” which are used for fine rubies and sapphires.

While the terms “pigeon blood red” and “royal blue” have long been used to describe the finest quality stones, there has never been a definitive agreement as to the precise colors and quality criteria corresponding to the two terms, the labs said.

SSEF and Gübelin both independently had developed their own criteria for using those color terms. But, now, in order to bring clarity to the industry and unify standards, the labs have compared their criteria and made a few minor changes in order to harmonize their color and quality standards, they said.

For a ruby or sapphire to qualify for use with the terms, the color has to be “an intense, saturated and homogenous red or blue,” the two labs said. The exact ranges of hue, saturation and tone are defined by a set of master stones.

“Pigeon blood red” is described as a red color with no apparent modifiers such as blue or brown, though a minute purplish tint is acceptable. The body color of a stone that can be deemed as this color also is complemented by a strong fluorescence when it is exposed to ultraviolet light.

“Royal blue,” meanwhile, is best described as a saturated blue color, either pure or with a very slight purplish tint. 

In terms of quality, the terms can be applied only to rubies and sapphires that exhibit fine qualities and have not undergone any modification of color and/or clarity; any type of treatment disqualifies the stones from being described by these color terms.

Additionally, they must be relatively free of eye-visible or dark inclusions and must show a homogenous color distribution with vivid internal reflections, according to the labs.

The size of the stone is not taken into consideration, so small rubies and sapphires still may qualify for these two color terms.

“Clearly, such stringent sets of criteria implies that only a very small percentage of rubies and sapphires qualify,” said Daniel Nyfeler, managing director of the Gübelin Gem Lab. “This is in line with the experience and belief of both Gübelin and SSEF that historically only exceptional rubies and sapphires were attributed these quality terms.”