Orange diamonds, greatly admired for their opulent colour, owe their beauty to broad absorption across the blue (480Nm) portion of the visible colour spectrum. The colour is caused by both H3 and H4 colour centres.
Pure mandarin to pumpkin, often Type IIa diamonds, are the rarest and most valuable hues. These are followed by pinkish Orange, Pink-Orange, yellowish Orange, Yellow Orange. Brownish Orange (‘Amber’) and Brown-Orange diamonds come last and typically represent stones commonly referred to as deep on the GIA scale which are often dark in tone yet only score moderately in orange colour saturation. Such stones may also sometimes be described as ‘burnt’ orange. They are not to be confused with the general observation that Orange, when dark, tends to mimic brown. This is particularly true when orange is present as a secondary hue, a good example being Orangy Pink diamonds.
In terms of fluorescence Type, Ia orange diamonds have been known to appear blue or green whereas Type Ib diamonds only rarely feature yellow to orange fluorescence which intensifies the body colour.
Although fine quality orange diamonds remain very rare, their demand is not quite on par with that of the primary hues.
Countries producing Orange diamonds notably include the Democratic Republic of Congo known for its ‘Congo-Caramels’ and the Republic of South Africa.