The cabochon cut is one of the oldest and simplest cut of stone. It is often used to display colours and different optical effects in opaque and translucent stones, meaning it is often favoured for coloured gemstones and very rarely used for diamonds. This cut means the stone has been shaped and polished as opposed to faceted; the top of the stone is often domed and the bottom is usually flat. This round polished surface is extremely difficult to create in a diamond because of the hardness of the stone, but does create a very unusual effect. It is often used for opaque stones and stones that are too soft to be faceted, such as amber.
Cabochon cut gemstones are sometimes seen as a less desirable form of gemstone in comparison to faceted stones, which people have attached much more value to. This may be because low grade materials are traditionally used for cabochons and the best gem materials are usually kept for faceted stones, but you can still find the majority of gemstones in a cabochon cut.
The cabochon cut can vary in shape, they aren’t always round. The shapes are the same calibrated sizes as those of a faceted stone, but the weights are different. The profile of the surface can range from something very low and flat to something with a very high ‘bullet’ shape. The base is often flat but can also be rounded to make the most of the colour in the stone.
Cabochons are often used to display interesting optical effects such as stars and cat’s-eyes or those of an opal or moonstone. When the light reflects from the stone’s internal features such as fibrous or needle-like inclusions or cavities, it can create different effects such as the star (asterism) or a cat’s-eye (chatoyancy). If there is just one set of parallel fibres it will create the cat’s-eye effect but with two, three or four that cross over each other, it can create a star shape. The cabochon cut is the best way to display these interesting effects.