Native Cut, Windows, and the Cost of Recutting

A cutter at the source is paid against the weight he returns. Every decision after that follows. Depth stays in the stone because depth is weight. The girdle stays thick because thickness is weight. The culet drifts off centre because recentring costs weight.

Why a window opens

Corundum has a refractive index near 1.76, which puts the critical angle at roughly thirty-four degrees. Light striking the pavilion steeper than that reflects back up through the crown. Light striking shallower passes straight out of the bottom of the stone.

A window is that second case, made visible. Hold the stone over print. If you can read through the middle, the pavilion is too shallow to return light and the centre of the stone is dead — not dark, dead. Colour cannot come out of a region that is transmitting rather than reflecting.

Cutters do not open windows out of ignorance. A shallow pavilion spreads a given weight across a wider face, and a wider face sells. The window is the price of the spread.

Orientation and colour

Corundum is dichroic: ruby and sapphire show two different colours along two different crystal directions, and the face-up colour depends on where the table sits relative to the optic axis. Oriented one way, a sapphire faces up a clean blue. Oriented another, the same crystal carries a greenish or violet cast.

The best colour orientation and the best weight orientation are frequently not the same orientation. At the source, weight usually wins.

Whether to recut

Recutting is subtraction. The stone loses weight — sometimes a little, often a fifth or more where the geometry is badly off — and gains brilliance, symmetry, and a face-up colour that holds through the tilt. Whether that trade pays is arithmetic, not sentiment.

Price per carat rises with size and rises faster with quality, so a recut that lifts a stone from windowed to lively can move it into a higher band and the higher band can more than cover the weight surrendered. It can also fail to, particularly if the loss carries the stone under a round weight the market cares about. That curve, and where it steps, is worth understanding before you commission any recut.

Two practical points. A certified stone that is recut needs a new report, because the old one describes measurements that no longer exist. And recutting cannot add what was never there — it redistributes light. It does not create colour, and it will not remove an inclusion sitting under the table.

Weight is what a cutter is paid for. Light is what a stone is worth. Those are not the same instruction, and the stone in front of you is the record of which one he followed.