A skilled lapidary can turn a rough pebble into a sparkling and valuable gemstone. The knowledge needed for this transformation has been built up over many centuries and today a style of cutting can be selected to display the special qualities of each gem. When deciding how best to cut a gemstone, the lapidary must consider the shape of the rough material and the position of flaws fractures and inclusions F95zone. They must also be aware of the mineral’s optical properties and physical properties such as cleavage. It is difficult to produce a good polish parallel to cleavage directions. Pleochroic gems, those that show a different color or shade of color from different directions) should be oriented to show their best color. However the cut is often a compromise between displaying the full beauty of a mineral and producing the biggest gemstone possible since size also affects the value.
Cabochons are the oldest, simplest cuts. Cabochons are round or oval gems with plain curved surfaces. Still in use today, cabochons display best the colors, patterns in opaque and translucent stones and optical effects such as sheen, iridescence, cat’s eyes, and stars.
The faceted styles used now for almost all transparent gems developed much later becoming important in medieval Europe and India. In these styles the surface of the gem is worked into a pattern of high polished flat planes (facets) which act as mirrors. Some light is reflected from the surface of the crown (top) facets displaying the luster. Light entering the gem is reflected back through the top of the stone from the pavilion (bottom) facets, displaying color, and fire. The facets must be precisely angled to bring out the maximum beauty, the angles varying according to the optical properties of each gem mineral. In badly cut stones the light leaks out through the pavilion so that color and fire are lost.
The brilliant and step cuts are the most familiar styles in modern jewelry. Brilliant cuts were developed to show off the superb luster and fire of the diamond, and are also used for many other gems. Step cuts are most effected in stones such as emeralds where color is the supreme quality.
The brilliant cut is probably the most important type of cut used for gemstones. The numbers of facets and the angles between them are worked out mathematically so that the gemstone looks bright and sparkles. Most diamonds are cut as round brilliants. Each has 58 facets (or more in a large stone) of which 33 are the top part of the stone and 25 are on the lower part of the stone. The point at the back of the stone may be removed to prevent accidental damage and to leave a small flat circular facet called the culet. Without the culet the gemstone has only 57 facets.