If you see triangle and kite shaped facets on a gem, it is a brilliant cut stone.
The “Brilliant Cut” or round cut is the most popular cut for Diamonds and is often used for transparent coloured gemstones as it is an ideal shape for maximising the light returned through the top of a gem.
The brilliant cut we know today has been developed throughout recent history by a number of cutters. It was first introduced in the mid 17th Century and at that stage featured 17 facets on the crown. A Venetian polisher called Vincent Peruzzi increased the number of facets to 33 and by the end of the 17th century, the Lisbon cut and Brazilian cut featured 58 facets, giving rise to a dramatic increase in the gem’s beauty through greater dispersion and higher brilliance.
In 1919, Marcel Tolkowsky studied the round brilliant cut and detailed geometric calculations to further improve the cut. He specified the exact angles of the facets and the percentage of the gem that should be above and below the girdle in order to maximise the brilliance and fire seen in a Diamond. Even today, almost 90 years later, Tolkowsky’s calculations are still adhered to by most Lapidarists when cutting round brilliant cut Diamonds.
The modern round brilliant cut consists of 57 facets (sometimes 58 if at the point where the pavilions meet, a small facet is added running parallel to the crown). There are 33 facets cut on the crown and 25 on the pavilion.
Please note that the brilliant cut is not exclusively used on round gemstones and if you see an oval, trilliant etc, where the facets appear to be a mix of triangles and kite shapes, then that is a brilliant cut.
In fact nearly all cut gemstones fall into one of just four main categories: either they are fancy cut (no pre-defined arrangement of facets), cabochon cut, step cut or brilliant cut. It is important not to confuse a gem’s cut with a gem’s shape. A heart shaped gemstone is exactly that, a heart shaped gem stone; the cut of a heart shape is normally a brilliant cut.
