Lumpy Diamonds

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

The term ‘lumpy’ describes diamonds which are too high or too thick compared to the proportions standard in any particular period. Up to the beginning of this century the two sets of main facets were supposed to meet at right angles at the girdle—that is, with both crown and pavilion angles of 45°. The crown height had to be half the pavilion depth, and the culet just large enough to act as reflector of the incident light. These proportions, developed in te sixteenth century, varying slightly according to the shape dictated by the rough, resulted in spectacular light effects, and diamonds with these classic proportions remained much in demand for nearly three centuries.

However, only one gem could be extracted from each crystal, and fashioning involved the long and arduous process of hand bruting, so it was not surprising that many cutters decided to save labor and leave the stones lumpy. They sacrificed a great deal of brilliance but saved weight, and were able to find a perfectly satisfactory market for these diamonds, at a slightly lower rate per carat, among a clientele lacking any appreciation of true quality.

Mawe’s ‘blunder’ was a further factor responsible for the belief that the overall height of a diamond should be equal to its width. As late as the 1930s I came across people with this conviction. At that time large quantities of old-fashioned lumpy diamonds were still on the second-hand market. These have all been recut by now but, alas, so have most of the beautiful 45° cuts.

The introduction of modern mechanical sawing has resulted in the possibility of substantial weight retention since it enables two gems to be cut from one crystal and eliminates the temptation, through sheer lack of judgement, to produce lumpy gems. This innovation, and the introduction of electricity to supercede candlelight, have brought new desired proportions to the Brilliant Cut. The overall height has been reduced from the classic optimum of 70 per cent to the new height of only 60 per cent.