The GRS Pigeon's Blood designation is a proprietary colour classification issued by GemResearch Swisslab (GRS) of Lucerne, Switzerland, applied to rubies whose colour meets the laboratory's defined standard for vivid red with medium tone and high saturation — the chromatic ideal historically described in the Burmese trade as ko-twe, or pigeon's blood. First formalised by GRS founder Adolf Peretti in the late 1990s and early 2000s, the designation appears as a supplementary notation on the GRS report and has become one of the most commercially significant colour calls in the coloured-gemstone market, capable of materially influencing auction estimates and private-sale prices for qualifying stones.

Historical and Trade Context

The phrase "pigeon's blood" has circulated in the ruby trade for well over a century, originating in the gem markets of Mogok, Burma (present-day Myanmar), where it described the finest saturated red rubies with a faint bluish overtone — a colour likened to the first two drops of blood from a freshly slaughtered pigeon. For most of that history the term was entirely subjective, applied inconsistently by dealers, auction houses, and buyers with differing visual references. A stone described as pigeon's blood by one merchant might be called merely "fine red" by another. The absence of a standardised definition created persistent ambiguity in auction catalogues and trade correspondence alike.

GRS addressed this ambiguity by developing a proprietary colour reference system grounded in spectrophotometric measurement and visual comparison against calibrated master stones. By anchoring the designation to reproducible instrumental and visual criteria, GRS transformed what had been an evocative trade phrase into a defined, certifiable colour grade — a development that proved both commercially powerful and, in some quarters, controversial.

The GRS Colour Standard: What Qualifies

GRS defines its Pigeon's Blood colour as a pure to slightly purplish red of medium to medium-dark tone and very strong to vivid saturation, with no visible brown or orange modifier. The laboratory evaluates colour under standardised lighting conditions and compares the stone against its proprietary reference set. Key parameters include:

• Hue: Red (R) to slightly purplish red (sR), with no appreciable orange or brown component.
• Tone: Medium to medium-dark — light stones and very dark stones are excluded regardless of saturation.
• Saturation: Very strong to vivid; the colour must appear fully saturated under standard daylight-equivalent illumination.
• Fluorescence contribution: Strong red fluorescence under ultraviolet, characteristic of corundum with low iron content, is considered a positive attribute and is consistent with stones that qualify, though it is not itself a criterion for the designation.

The designation is origin-neutral in principle: GRS will apply it to any ruby meeting the colour standard regardless of provenance. In practice, however, the overwhelming majority of rubies receiving the Pigeon's Blood call originate from Mogok, Burma, or — since the emergence of Mozambican ruby on the international market in the early 2010s — from the Montepuez deposit in Cabo Delgado Province. Rubies from other localities, including Mong Hsu (Burma), Vietnam, and Madagascar, may qualify but do so less frequently owing to differences in typical colour character.

The GRS Report and Appendix System

GRS issues its colour designations as a supplementary appendix to the main gemological report rather than as a field within the standard report body. This appendix, sometimes referred to in the trade as the "colour comment" or "type" appendix, may carry one of several colour designations — Pigeon's Blood being the most prestigious for ruby, with Royal Blue and Cornflower Blue serving analogous functions for sapphire. The appendix is issued only when the laboratory's graders reach consensus that the stone meets the relevant standard; borderline stones receive no colour designation rather than a lesser one.

The report also records geographic origin, heat-treatment status, and any clarity enhancements. A ruby bearing a GRS Pigeon's Blood designation alongside a "no indications of heating" (NIH) determination represents the highest combined certification outcome available from that laboratory, and such stones command the strongest premiums in the market.

Market Impact and Price Premiums

The commercial weight of the GRS Pigeon's Blood designation is well documented in major auction results. Rubies certified with this colour call by GRS — particularly unheated Mogok stones — have consistently achieved prices at or above the upper end of pre-sale estimates at Sotheby's, Christie's, and Bonhams. Industry observers and dealers active in the coloured-stone market broadly acknowledge a price premium of roughly 20–40 per cent for rubies carrying the designation compared with comparable stones of similar quality without it, though the precise differential varies with size, clarity, and origin.

The premium reflects several converging factors: the designation provides a standardised, internationally recognised vocabulary for a quality that was previously described only in subjective terms; it offers buyers — particularly those purchasing at auction or through intermediaries — a degree of objective assurance; and it has been adopted as a reference point by major auction houses in their catalogue descriptions, effectively embedding the GRS terminology into the secondary market's language.

Relationship to Other Laboratories' Standards

GRS was the first major laboratory to formalise and systematically issue the Pigeon's Blood designation, but it is no longer alone in doing so. The Gübelin Gem Lab (Lucerne) and SSEF (Swiss Gemmological Institute, Basel) subsequently introduced their own equivalent colour comments — Gübelin using "Pigeon's Blood Red" and SSEF using "Pigeon Blood" — each grounded in the respective laboratory's proprietary colour reference. The three Swiss laboratories have broadly converging standards, and a ruby receiving the designation from all three simultaneously is considered to have the strongest possible colour certification, a circumstance that commands a further premium in the highest tier of the market.

The Gemological Institute of America (GIA), by contrast, does not issue named colour designations such as Pigeon's Blood or Royal Blue on its coloured-stone reports, instead providing colour grades expressed in terms of hue, tone, and saturation using its own descriptive system. This difference in approach means that GIA reports and GRS reports are not directly interchangeable for the purpose of colour designation, and buyers accustomed to the Swiss laboratory system should be aware of the distinction.

Criticisms and Limitations

The designation has attracted criticism on several grounds. Some gemmologists and dealers argue that reducing a nuanced aesthetic quality to a binary pass/fail determination — a stone either qualifies or it does not — oversimplifies a continuum of colour and introduces a sharp commercial cliff-edge that does not reflect the gradual nature of colour variation. A ruby just below the threshold may be visually indistinguishable from one just above it, yet the market treats them very differently.

There is also the question of consistency across time and between graders. Although GRS employs calibrated reference stones and standardised lighting, colour grading retains an irreducible subjective component, and there are documented instances of stones being resubmitted to the same or different laboratories and receiving different outcomes. The laboratory community has acknowledged this challenge and continues to refine its methodologies.

Finally, the commercial weight of the designation creates an incentive for selective submission — owners of borderline stones may submit repeatedly until a favourable result is obtained — and for the designation to be used as a marketing instrument in ways that can obscure other quality factors such as clarity, cut quality, and the nature of any treatment.

Practical Guidance for Buyers

For buyers evaluating a ruby accompanied by a GRS Pigeon's Blood designation, several points merit attention. The report date matters: GRS has refined its standards over time, and reports issued before approximately 2010 may reflect earlier, somewhat more permissive criteria. The treatment status recorded on the report is equally important: the designation applies to both heated and unheated stones, and the two categories occupy very different market tiers. Buyers should also verify that the report is current and has not been superseded by a re-examination. Finally, the designation should be considered alongside — not instead of — direct visual assessment of the stone under a variety of lighting conditions, since laboratory grading is conducted under standardised illumination that may not replicate the conditions under which the stone will typically be worn or displayed.

Further Reading

• GIA Gems & Gemology: Ruby
• GIA research on ruby colour grading
• Lotus Gemology: Pigeon's Blood Ruby — What Does It Mean?