Extinction

Extinction is the dark areas in a stone's face-up view where facets return no light to the eye, most visible in deep-pavilioned and dark-toned stones: a Thai or Australian sapphire cut deep to hold colour, a garnet with too much tone, a tourmaline seen down its dark axis. A little moving shadow is life; the play of light and dark as the stone rocks is what makes a faceted stone read as faceted at all. Large fixed dead zones are the problem, because they flatten the colour the stone paid for in tone. A royal blue with a third of its face in black is a darker, smaller stone than its weight suggests.

Extinction is the opposite failure to a window. One leaks light through a pavilion cut too shallow, the other swallows it in a pavilion cut too steep or a body too dark, and the space between the two failures is simply good cutting.

In practice

No laboratory grades extinction. GIA's coloured stone reports carry no cut grade, and neither do those of the Swiss houses; the report gives a cutting style, "cushion mixed cut" or the like, and measurements, and stops there. It is a judgement made at the desk, which is why photographs sell stones and daylight buys them. A ring light fills extinction, and a shop's spotlights make it dance. Look at the stone under a north window or diffuse daylight, hold it still at arm's length, and see how much of the face stays dark. A pavilion much deeper than the trade norm for the shape is a warning, and so is a stone the dealer describes as dark-toned.

Ask to see the stone still, in daylight, beside something lighter of the same colour. If the extinction is a matter of cut, a recut may fix it at a cost in weight. If the body is simply too dark, no cutter can lift it.