The Mirror, Mirroring Or Spread Table Cut

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

The term ‘Mirror’ dates from the late fourteenth century and is frequently found in inventories of the early fifteenth century where gems were described as fait en façon de mirouer or mirour de diemant. It was also used in the names of famous diamonds such as the Mirror of Portugal and the Mirror of France. The mirror was very popular as a form of decoration and a symbol of luxury during the Renaissance. Applied to diamonds, the term described the striking light effects in certain Table Cuts. The term will not be found in modern diamond literature, but it is so appropriate for the cut that I feel it should be brought back. A Spread Table Cut looks exactly like a mirror, both in its outline and because of the strong reflection of light from its large surface—a far stronger reflection in diamonds than from a mirror made of metal or glass.

The term was applied to every diamond that resembled a mirror but it was not enough for well-polished facets to give attractive surface reflections (adamantine luster). Brilliant reflections from the interior were necessary as well, and these could only be achieved if the pavilion angle were about 45°. However, as it is unlikely, at least until after the Renaissance, that these combined light effects were perceived as separate phenomena, it seems logical to apply the term ‘mirroring’ to any historic cut with the quality of brilliance. These terms were introduced to French during the twelfth century, and only replaced by the term brilliant (used as an adjective) somewhere around 1564. After 1608 Brilliant (now used as a noun as well) gradually came to describe all faceted, pavilion-based diamonds.

The Mirror Cut is considerably less expensive to fashion than the High. Its general geometry is similar, especially in the pavilion with its relatively small culet which reflects light back through the crown—as it does, of course, in any Table Cut diamond with 45° angles of inclination in the main facets. The size of the table in a Mirror Cut appears to have been influenced by the square root of two and by the simple arithmetical proportions proposed by Luca Pacioli in 1509. Both are of geometric, though not Pythagorean, origin. The table would be around 70.7 percent of the overall dimension of the girdle. A figure which springs to mind when one thinks of Mirror Cut diamonds is that of a ‘man and a circle inscribed in a square’. A man and circle inscribed in a square, after a sixteenth century edition of the writings of Vitruvius could be a diamond and its table facet, in a ratio of 2:1, giving a table size of 70.7 percent. A man in a square , after a drawing by Cornelius Agrippa in the 1533 edition of Occulta Philosophia would, if applied to geometry of diamonds, suggest a table size of almost 80 percent.

In fact, the crown was often so low that the table was sometimes as much as 90 percent of the width of the girdle. A facet of this size acts, literally, as a mirror, and the reflections from the pavilion facets and the culet further increase the brilliance. However, only High Table Cuts, and then only those with correct proportions and perfect symmetry, display a combination of both brilliance and fire. In the old days gems of this type could be quite easily fashioned, with very little loss of weight, from fairly thick triangular rough such as macles, which were plentiful and much less expensive than octahedrons. A ‘was’, produced by cleaving, was equally suitable.

The Mirror, Mirroring Or Spread Table Cut (continued)