A marquise-cut diamond is boat or eye-shaped and can be called a navette. Not often used, the term navette is a French word meaning "little boat", because it resembles the hull of a sailboat.
Today, the marquise is a modified brilliant-cut; however, the earliest-known report of this shape stems from the Marquise de Pompadour, famous mistress of Louis XV. The new diamond shape appeared in Paris and was named in her honour. It was most likely a rose cut marquise shaped diamond.
There are several ways to cut a marquise diamond and there is no set number of facets. Typically, as with a round brilliant cut, the crown of a marquise has 32 facets, however, there are two less pavilion facets, making a total of 55 facets - plus or minus a culet. Generally, a 2:1 length-to-width ratio is preferred.
As with oval stones and pear shapes, the marquise cut generally has a "bow tie" visual effect. The "bow tie" appears as a dark bow tie-shape running across the width in the middle of the stone. This is not caused by leakage as was commonly thought. The actual cause is the same as a 'nail head' or dull centre as seen in an overly deep round brilliant cut; the result of one's head obstructing the generally brighter lights and areas above. For a better understanding, look at a marquise with a bow tie and identify the dark portion. Now take a sheet of A4 paper and poke a hole in the centre with a pen. Peep through and you will see the bow tie has disappeared.
Another visual effect seen in the ends of a marquise cut stone is that of the "crushed ice" effect, which gives an appearance of tiny pinfire bright speckles.
Variations of the marquise cut have occurred over time for different purposes; some are attempts to avoid the appearance of the bow tie, while others are designed to spread the crushed-ice effect seen in the ends of the marquise cut right through the centre of the stone. This latter development is especially effective at increasing the face-up colour of fancy-shaped diamonds - the crushed effect is a consequence of a longer ray path as light bounces around inside the diamond several times before escaping.
The marquise cut makes up only between 1 and 2 per cent of all diamonds by value (and even less by quantity); however, it is often found in very large sizes because it requires very large and irregular-shaped rough, such as that often found in type II diamonds. The marquise's appeal may be said to stem from the fact that the cut allows for a surface 20 per cent larger than other cuts, so the stone appears quite large.
On close examination, the marquise diamond will often have evidence of remaining inclusions or naturals on the girdle which itself may vary considerably in thickness. This is due to marquise cut diamonds (as well as heart shape stones) often being made out of low-clarity goods: the cut lends itself to masking inclusions while maximising yield.
During the cutting process there is larger risk of breakage while bruting the girdle outline. The bruting process involves several steps in placing the rough offset in a lathe where, as a diamond rotates around in an arc, it hits another diamond which grinds or brutes the shape. This impact causes much stress which can result in breakage. The introduction of laser sawing - burning or vaporising - removes this risk.
Setters should use a small ball burr to open the area immediately around the tips to ensure there is little or no pressure exerted that could result in a chipped tip.
Jewellers should be aware that the pointed ends are easy to break during setting; the points are even more fragile than the corners of a princess-cut.
Marquise is popular in drop earrings and pendants. It will also make a very distinctive ring.