The Knob Cut

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

The Knob Cut (also known as the Nail Cut, Duke Cut and occasionally Prince or Prinz Cut) was a development of the standard Pyramidal Cut, in that the original, possibly damaged, apex was ground away to make a tiny table facet. A cubic formation modifying the points of an octahedron is quite often found in nature. This no doubt inspired both the Knob Cut and the blunt corners in some pyramidal cuts, as well as various types of tables. This particular modification of the point cut seems to have been popular from the second half of the fourteenth century to the beginning of the sixteenth, and can be seen in a number of contemporary paintings. It is described in some inventories as Nail Cut, the term referring to the crown, which is shaped like the head of an antique nail.

An octahedral rough with broken apexes can be improved by ‘lowering’—that is, by grinding its large faces until the desired sharp apex is obtained. However, this is a delicate and laborious operation and it is easier to fashion the damaged, missing or misshapen point into a small table. Additional facets may be applied, for instance on broken edges. The Knob Cuts were fashioned in this manner, and it is clear that they were precursors of the Table Cuts.

Very early Knobs can be seen in German engravings of royal crowns dating from the beginning of the twelfth century. In a number of inventories tiny Knob Cut diamonds are described as representing the nails that pierced Christ’s hands and feet on the cross. In the Kleinodienbuch der Herzogin Anna (c.1550) there are several illustrations by Mielich of jewels belonging to Anna, Duchess of Bavaria. One of these is a natural Point reproduced with a clear, full-sized reflection, but symmetrized just sufficiently to give a tiny Knob facet at the top. A crown sketched for Christian IV of Denmark by Corvinianus Sauer (1594) also features Knob Cuts. In a portrait by Rubens, dating from about 1620, the French Queen, Anna of Austria, wears a large necklace which displays several Knob Cut diamonds, all fashioned from Hogbacks—that is, long rectangular stones.

Only a very few Knob Cuts have survived; apparently most of them were recut into Tables. One important exception, a 10 ct yellow diamond called the Jonquil (on display at the Musée ďHistoire Naturelle, Paris), has been part of the Royal French Treasury since at least the seventeenth century. The Jonquil is richly faceted and has the same arrangement of twenty four facets in both the crown and the pavilion. Both the table facet and the culet are octagonal and the same size as each other. This disposition of facets is very like that of the relatively modern Split Brilliant Cut. Even the octagonal angles have to some extent been retained.