The Old Mine cut is the cut that existed before the modern round brilliant. From roughly the 1700s until 1919 — when Marcel Tolkowsky calculated the ideal-cut proportions and the industry standardised — almost every diamond cut was an Old Mine. Cushion outline, high crown, small table, open culet, fifty-eight facets cut by hand.
It was designed for candlelight. This is the crucial fact. Until the early twentieth century, jewellery was worn primarily by candle, oil lamp, and gas light — warm, low-intensity, directional sources. The Old Mine's geometry — its steep crown, its small table — is optimised for these conditions. It throws back fire, the warm rainbow dispersion that warm light excites, rather than the cold white sparkle that overhead daylight produces.
Under modern lighting, an Old Mine looks different from a round brilliant. It is not as bright. It is not as scintillating. What it has instead is fire: large, slow, coloured flashes that move through the stone as it tilts. Modern brilliants compress fire down to fast, fine sparks. The Old Mine lets fire breathe.
Because every Old Mine was cut by hand, no two are identical. The outline is cushion-shaped but irregular — slightly squarer in one example, more pillow-like in another. This irregularity is the cut's signature. A modern machine-cut diamond is perfectly symmetrical; an Old Mine carries the hand of its cutter. When you choose an Old Mine, you are choosing a stone that was once an individual decision rather than a calculated output.
Lab-grown rough lets us cut Old Mines today in a way that would be economically impossible with mined stones — the deliberate inefficiency of the cut (a modern brilliant retains more of the rough) costs less when the rough itself is reasonably priced. This is one of the cases where lab-grown opens up a possibility that mined diamonds quietly closed.