The Significance Of An Adequate Culet

(via Diamond Cuts in Historic Jewelry:1381-1910) Herbert Tillander writes:

When the imperfections of historical diamonds are commented on, the point of criticism is usually not that the proportions are wrong but that the culet is thought to be too large. In open settings the culet looks like a hole, and in closed settings like a black spot against the corroded foiling.

The late E F Eppler is the only person to have made a scientific study of the significance of a large culet. He writes of Brilliants with 45° angles, but everything he says applies equally well to Full Table Cuts: ‘For this particular cut the output of light is surprisingly high....and depends mostly on the large culet which therefore has a great importance.’ He calculates the output of light to be 18.9 percent of the incident light, and adds: ‘With an increase in the angle of incidence, the output rises at first until, at approximately 30°, a drastically sharp drop occurs. This first part of the curve, representing the output of light for the angles of incidence between 0° and 30°, is caused simply by the culet. Increased angles again cause a peak in output at 45°, which is followed by further reduction until zero is reached at 90°.’ Later in the same article Eppler comments: ‘It is astonishing that the diamond cutter of former time found an improvement in the brilliance by applying a culet not by calculation but by practice only. In reducing the angles in crown and pavilion the culet has less importance and in the modern fine cut...the absence of the culet is an absolute necessity, if it is not applied to minimize damage.’