Round Brilliant Cut Diamonds

The most common cut nowadays is the round brilliant cut. This is generally based on the mathematical model established by Towkolsky in 1919. However, this cut was known at least as far back as 1564, when the term was introduced in France.

In 1691, an inventory of the diamonds of Louis XIV was compiled, which used the term extensively. At that time, however, is also encompassed some other cuts, including Sancy cuts, Briolettes and Stellar cuts.

The brilliant cut developed from several cuts which passed out of fashion; Burgundian point cuts, Star cuts and Tailles en Seize. These cuts sparkled less in candlelight parties, which were all the rage at the time. At that time, most diamonds were Rose Cuts, which I have written about in the post about antique diamond cuts. This presented a problem, as the flat bottom facet of the Rose cut  left it looking dull in candlelight.

The round brilliant developed naturally, being a marriage of the Sancy cut for the top half, and the pointed star cut for the bottom half.

The star pattern on the bottom half, when put together with the Sancy, is the basis of the round brilliant cut we all know so well.

(The natural shape of diamond rough, a dodecahedron, lends itself to the development of the brilliant cut, as the facets arrange well along the different grains of the diamond.)

The large pavilion facets, and slight asymmetry give great fire, and the irregular shape and size of different facets give amazing light reflection; the light dances around in a way not seen in other cuts.

The earliest brilliant cuts followed a round outline, as this is the general shape of the rough. However, 17th century taste called for a different shape of diamond, with more fire and greater life. From this was born what we typically call a cushion cut diamond. This was the standard cut until the 19th century, when mass-production techniques began to be applied to diamond cutting, and the round brilliant cut came to be the standard, a cut which evolved gently into today’s modern round brilliant cut, as outlined in Towkolsky’s famous research paper in 1919.

An early round cushion can be seen below; notice the small table, less than 50%, with gives added scintillation.

round cushion

The old cushion cuts are either square or rectangular in shape, with rounded corners, and sometimes slightly rounded sides, as seen in the 3 carat diamond below. They often have slightly irregular shapes and outlines, but this adds to the vibrant fire. This example is broadly rectangular, with rounded edges. It also has a small table, and has a beautiful reflection pattern.

cushion cut

If you look closely at many antique cuts, you can still see traces of the original rough crystal on the girdle of the stones. These are called naturals, and can sometimes be breathtakingly beautiful, with gorgeous trigons. This is my favourite part of a diamond, and something I love seeing!!!

For a lot of this information I am greatly indebted to Diamond Cuts in Historic Jewellery by Herbert Tillander, published by Arts Books International.

Weldons is Dublins leading specialists in antique diamond engagement rings, with a wide selection of beautiful and unique rings. Please do call in for a visit!