Gemstone Faceting

The most common method of fashioning a gem is to cut the surface into a number of flat faces, known as facets. This gives the stone its final shape, or ‘cut.’ The craftsman, or lapidary, who cuts the stone aims to show its best features, taking into account its color, clarity, and weight. He may, however, have to compromise to retain weight and value.

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How Stone Faceting is Done?

There are several stages in the cutting of a gemstone, each of which may be carried out by a different expert. A rough diamond is usually fashioned into a brilliant cut. This is the most popular for this particular stone because it maximized the gem’s naturally strong light dispersion. However, because each stone is a different shape, or has imperfections within it, or because retaining the weight is of paramount importance, the cut in its ideal form (the ‘make’) may not be possible.

Nevertheless, the essential aim is to make diamonds bright and ‘sparkling’ to show flashes of color called fire. To this end, the size, number, and angles of the facets are mathematically calculated. The rough crystal is sawn or cleaved to obtain a basic workable piece, then turned on a lathe against another diamond to give it a round shape. The facets are then cut and polished in stages, and the stone is given a final polish before mounting.

Below, we highlight the steps in faceting a stone (a diamond, in our example).

1. Rough

A rough stone is selected for faceting.

2. Cut

The tope is cut off, and the stone is rounded on a lathe.

3. Grind

The central facet – the flat table – ground first, then the bezel facets.

4. Top and Bottom

More facets are put on in groups and in sequence: the star facets and upper girdle facets on the crown; then the lower girdle facets and the culet on the pavilion (the underside).

5. Finishing

A ‘brillianteer’ then adds a further 24 facets above the girdle and 16 below.

6. Mounting

After a final polish, the stone is mounted in precious metal.

Types of Cuts in Faceting

1. Brilliant-Cuts

The brilliant cut is the most popular for diamonds and many other stones, particularly colorless ones. It ensures that maximum light is reflected out through the front, giving brightness and fire. Variations in the outline give the oval, the pear-shaped pendeloque, and the boat-shaped marquise or navette.

2. Step-Cuts

The step-cut (or trap-cut) shows colored stones to advantage. It has a rectangular or square table facet and girdle, with parallel rectangular facets. The corners of fragile gems may be removed, making octagonal stones. Emerald is commonly fashioned in step-cuts.

3. Mixed-Cuts

Mixed-cut stones are usually rounded in outline, with the crowns (above the girdle) cut as brilliants, and the pavilions (below the girdle) step-cut. Sapphires, rubies, peridots, and the most transparent colored stones are cut in this style.

4. Fancy-Cuts

These have several possible outlines, such as triangular, kite-shaped, lozenge-shaped, pentagonal, or hexagonal. The cut may be used for rare gems, or to make the most of a flawed or irregular-shaped gem. A heliodor is usually fashioned in fancy cuts.