The cabochon cut is one where the gemstone is shaped and polished into a smooth, rounded dome shape, rather than being cut into facets which have angled surfaces. But why are some gemstones cut as cabochons instead of facets? In this piece, we will delve into the rationale for cabochon cutting and examine a selection of gemstones that are especially compatible with this type of a gemstone cut.
What is a Cabochon?
A cabochon is a type of gemstone cut that has a smooth, rounded top with a flat or slightly domed base. The origin of the term ‘cabochon’ can be traced back to the French word "caboche," which translates to "knob" or "head." Unlike faceted gemstones, cabochons have no sharp angles or edges. They are often used to showcase the natural beauty of a gemstone's colour and bring out specific optical effects of certain gemstone inclusions.
Generally, gemstones that are opaque or have a lower rating on the Mohs Scale, are cut en cabochon, meaning "in the manner of a cabochon" in French. On the other hand, transparent stones like diamonds are usually faceted.
Cabochons can be created in various shapes, including rectangles, pears, and circles, but oval shapes are most commonly found. The convex shape of the top surface creates a unique play of light that can enhance a stone's natural colours, patterns, and inclusions. This makes cabochons a popular choice for gemstones such as opals, turquoise, blue moonstones, and chrysoberyl cat’s eyes. Depending on the physical properties of a stone and the specific inclusions present within each specimen, certain sapphires, rubies and emeralds may also be cut en cabochon.
Figure 1: A Cabochon-cut Emerald (Source: Pinterest)
Why are some Gemstones Cut En Cabochon?
Some gemstones possess unique optical properties that can only be fully appreciated when they are cut en cabochon. For example, the asterism effect of star sapphires, and the adularescence in moonstones are all more pronounced when viewed on a cabochon-cut gemstone. The goal of the cabochon cut is to showcase the gem’s unique optical effects and natural patterns, giving the gemstone a fuller and denser appearance rather than a brilliant sparkle.
Cabochon cutting is not only popular for opaque gemstones but is also beneficial for softer gemstones that typically have a lower ranking on the Mohs Scale. This cutting style not only enhances the appearance of these softer gemstones, but also helps to protect them from scratches and blemishes, making them more durable and longer-lasting.
The Unique Optical Effects of Cabochon Gemstones
Cabochon cuts can enhance the optical effects and unique features of certain gemstones. Some gems have natural patterns, textures and specific inclusions that can cause effects such as bands, swirls, or star-like formations that can be better showcased through the smooth, polished surface of a cabochon cut. The following is a list of some of the most popular optical effects that are highlighted with a cabochon cutting style.
1. Asterism
When it comes to cabochon-cut gemstones, Star Sapphires and Star Rubies are amongst the most intriguing examples due to an optical phenomenon known as Asterism. Asterism creates a star-shaped pattern on the surface of the stone, which appears to dance or shimmer when the gemstone is viewed from different angles in shifting light. This effect is created by the presence of tiny needle-like inclusions called rutiles, within the sapphire that reflect light in a specific way. The cabochon cut is essential for displaying this beautiful effect, as the smooth surface helps to reflect and focus the light within the stone.
Figure 2: A Star Sapphire with exceptional Asterism (Source: GIA)
2. Chatoyance
Chrysoberyls represent a gem-quality mineral species frequently crafted into cabochon cuts. This mineral group includes Alexandrites and Chrysoberyl Cat's Eyes, which display a fascinating optical phenomenon called "chatoyance." Chatoyance is caused by the presence of parallel rutile fibres within the mineral, and results in a narrow light band that shifts across the stone's surface as it moves or rotates, reminiscent of a cat's eye. While chatoyance is observed in various mineral species like quartz and opals, chrysoberyl exhibits the most pronounced and sharp effect. The cabochon cut not only accentuates this captivating feature but also safeguards the delicate fibers responsible for it, making it a sought-after choice for jewelry.
Figure 3: A Chrysoberyl Cat's Eye showcasing a sharp Chatoyance
3. Adularescence
Adularescence is a phenomenon where a white or blue glow seems to emanate from beneath the surface of a gemstone. This effect is often seen on Moonstones, part of the Feldspar mineral group, which are often cut en cabochon to highlight their adularescence. As the stone is moved or rotated, its sheen shifts, creating a mesmerizing and shimmering effect reminiscent of moonlight dancing on water. This captivating appearance, along with the stone's subtle, dreamy glow, has led to its namesake. A cabochon cut helps to emphasize this effect by allowing the light to reflect and refract within the stone, creating a beautiful and mystical shimmer. The finest moonstone is a gem of glassy purity with an electric blue shimmer, known as blue sheen, which is only highlighted due to a cabochon cut. Moonstones can also exhibit chatoyancy or the cat's eye effect, which appears as a bright, narrow band of light that moves across the gemstone's surface resembling a cat's eye.
Figure 4: A Blue Moonstone with a shimmering adularescence (Source: GIA)
4. Play of Colour
Opals are gemstones that are renowned for their stunning Iridescence. In particular, Opals are famous for a unique optical effect called the ‘play of colour’. The play of colour is created by the diffraction of light on the microscopic silica spheres that make up the opal's structure. As light passes through the opal, it is split into different colours, creating a beautiful and vibrant display of hues that seem to dance and move within the stone. The cabochon cut is often used to showcase this mesmerizing effect, as it allows for a smooth surface that helps to reflect and refract the light within the stone.
Figure 5: An Opal with a rainbow-like Play of Colour (Source: GIA)
Cabochon-cut gemstones provide exclusive optical effects that remain mostly unattainable through faceted cuts. The sleek, domed surface of cabochons impeccably showcases phenomena such as chatoyancy and asterism in gems like chrysoberyls, moonstones, and star sapphires. In addition to their aesthetic appeal, cabochons have a rich history that dates back to ancient times, as they were the primary method for cutting and polishing gems before the advent of faceting. Their timeless charm continues to captivate jewellery enthusiasts and collectors alike. Whether it's the elegant, rounded appearance of cabochons, their capacity to emphasize a gemstone's finest attributes, or their adaptability for more delicate stones, cabochons present a versatile and alluring cutting style that accentuates the distinct qualities of each gemstone.
