Cutting styles

Two main cutting styles are commonly used in the trade: brilliant cut and step cut. The brilliant cut, which is known to enhance the facet reflections, is usually used for gems displaying high brilliancy and lustre. The step cut, which is known to concentrate colour, is used more for gems of low lustre and/or pale colour. Some cutters also combine the two cuts in a single stone, such as a brilliant-cut crown and a step-cut pavilion, to produce the best gem appearance.

Other less common cutting styles, such as rose cut and briolette, are usually associated with cheap or synthetic gems. Therefore, a natural gem of good quality, which was fashioned in such a style, would suffer a major decrease in its price.

Traditional shape or cutting style

Some gems are known by the trade as associated with a specific cutting style. Good examples for such gems are the emerald and aquamarine (which are associated with the cut-cornered rectangle step-cut style called ‘emerald cut’) and the blue sapphire (which is associated with the oval- and cushion-shaped brilliant cuts). These traditional cuts are constantly in big demand and usually go for a small premium.

Cabochon

A Cabochon, also known as cab, is a polished gemstone with a rounded domed top. Most cabochons are fashioned in an Oval or round shape but other shapes, such as pears and triangles, are common too. The cabochon cutting style may affect the price of a gem in two ways:

Cabochons are usually used for gems of translucent or opaque transparency (such as jade, lapis lazuli, turquoise, etc.) or gems with low clarity grade, where some inclusions are prominent. This is the main reason behind the dramatic reduction in price for such gems.

• Cabs are also used to produce optical effects, such as chatoyancy (cat’s eye) or asterism (star), which require a curved surface in order to be seen. In this case, the gem’s price is set according to a specific pricelist of the phenomena (e.g. star ruby pricelist).

Cut grades

Cut grade refers to the quality and preciseness of a gem's outline, its shape, the placement and alignment of its facets. These factors, when ideal, contribute to maximize the stone's appearance. The cut does not refer to shape or cutting style (e.g. oval, emerald cut, etc.), but rather to the outward appearance.

Unlike diamonds, each coloured stone possesses different properties and therefore there is no uniform cut which is ideal for all. Moreover, as the properties' range of a certain gem can be wide, a set of ideal cut measurements of one gemstone may not necessarily be suited to a different gemstone of the same variety.

A well-cut coloured gem should exhibit uniform colour, a minimum number of noticeable inclusions and attractive brilliancy. The precision with which a gem was processed, incorporating the proportions, angles, symmetry and finish of its polished facets, is important in judging its quality. Skilled processing will bring out the best possible colour with the highest clarity grade, and may enhance special optical features and lustre, which may increase the stone value.

The Cut grade is graded according to 5 quality levels (Excellent, Very good, Good, Fair and Poor.) The grade is evaluated by combining of three factors:

• Proportions – compares the gem's proportions to the overall appearance of the gem. Stones which are not cut in their well-suited proportions, may display over lightness or over darkness, or create "windowing" effect, which allows the light to pass through the stone without absorbing its colour and reflecting it back. When cutting a clear, lightly coloured stone, an effort should be made to expand the stone's pavilion. When the stone is dark, larger ‘window’ facets, which will allow more light to enter the stone and brighten it, should be made.
• Symmetry – inspects the gem's alignment of facets, as seen by the unaided eye and under magnification.
• Polish – inspects the smooth appearance of the gem's facets as seen under magnification. Noticeable abrasions and scratches may lower the grade.