Star sapphire engagement rings are a rare variety of sapphires that exhibit an unusual asterism under specific lighting. Asterism, which is caused by small needle-like inclusions of the mineral rutile, is responsible for the star sapphire’s shimmering rays. These sapphires can occur in almost every colour with the vivid blue hue the most desirable. Yellow, orange and green star stones are very uncommon. While most star sapphires only exhibit a white star, Thailand’s sapphires are famed for their gold coloured asterism.
The six-rayed-star effect can only be viewed under a strong source of direct light and proper cutting is critical for sapphire engagement rings, not only for the overall appearance of the stone, but to ensure a well-defined and properly oriented star. An ideal star should be perfectly centred when viewed from directly above, with each ray of equal length. The rays should also be bright, sharp and clearly defined, in good contrast with the stone’s background, and reaching from the crown of the cabochon to the base without interruption. However, you must remember that you will not be able to find a stone with all of these elements in perfect form, and if you do encounter a ‘perfect’ star, this is usually a sign that it has been man-made.
While the majority of star sapphires tend to be untreated, they can be subject to treatments to improve their colour or to artificially induce the star phenomenon. Those sapphires can sometimes be heated to intensify or enrich their colour but this must be done extremely carefully, at a modest temperature, in order not to obliterate the star-inducing rutile silk. You should look out for an overabundance of surface cracks when considering star sapphire engagement rings, for while these flaws are common in such stones, too many, as often seen in coloured enhanced stones, could weaken them. For these reasons, fine star sapphires are becoming increasingly more rare and difficult to find. Although occasionally weakened by treatments, star sapphires are typically very durable and are considered to be one of the hardest materials. While technically slightly softer than diamond, they lack cleavage that makes stone more resistant to damage.
Star sapphire engagement rings offer something completely unique and beautiful to every couple, and they actually used be viewed as powerful talismans that protected travellers. In fact, they were considered so powerful that it was believed that they would protect the wearer even after being passed on to someone else. One of the finest examples of such a sapphire is the ‘Star of Asia,’ currently displayed at the Smithsonian Institution in Washington D.C., which is an impressive 330-carats.
