Pigeon's blood

Pigeon's blood is the trade term for the most saturated pure red in ruby: red with no more than a whisper of purple, medium to medium-dark in tone, and lit from within. That inner light is fluorescence. Fine Mogok ruby is low in iron, so in daylight its chromium glows red on top of red, and the phrase has been tied to Burmese material for as long as Burmese material has been traded through Bangkok and Bombay. Nobody in Mogok, so far as we can tell, ever measured a pigeon. The term describes colour alone. It says nothing about heat, and nothing about where the stone was dug.

On a lab report

Several laboratories now grant the term under written criteria, and they do not agree. GRS prints "vivid red (GRS type pigeon's blood)" as a colour grade and will apply it to ruby from Burma, Mozambique and elsewhere, heated or not, provided the colour and tone fall inside its range. Gübelin and SSEF use it under a joint standard that asks for strong fluorescence and no indications of heating, and for a period confined it to Burmese stones before extending it to Mozambique material that meets the mark. GIA does not print colour trade names at all. So the same stone can be pigeon's blood at one house and simply red at another, and both are right by their own book. Treatment and origin sit on separate lines of the report, and a heated Mozambique ruby can carry the phrase honestly.

The premium belongs only to stones where a named laboratory has put the phrase in writing on a current report. Ask which laboratory, ask whether the stone is heated, and read the origin line before the colour line. Then take it to a north-facing window, where the fluorescence either fires or it does not.