Cat's Eyes and Stars

CUTS Images courtesy of Terry Coldham CAT’S EYES AND STARS Cat’s eye and star gems are prime examples of how inclusions can be an asset in coloured gems rather than a liability, explains the GAA’s KATHERINE KOVACS. When gemmologists refer to cat’s chrysoberyl cat’s eye although corundum crystal, the inclusions it from directly above. In the case eye stones, they say they display chatoyancy is found in numerous may align in such a way as to of cat’s eyes, it is best if the eye chatoyancy. The name cat’s eye is other gems. These include quartz, produce a six-rayed star. Think of runs along the length of the stone an apt description really: properly tourmaline, alexandrite (itself three sets of “cat’s eyes” in the rather than across the width, but cut, the gem displays a thin band part of the chrysoberyl group), one stone orientated at 60 degrees often cutters opt for the latter as running along the length of the beryls (not to be confused with to one another. Interestingly, stars it produces a stone with greater stone that reflects light back to the chrysoberyls, these include are often seen in sapphire and weight and therefore greater value. viewer. To display the effect, the emerald and yellow beryl), opal, ruby however cat’s eye stones are The best and rarest examples gem must be cut as a cabochon and garnet amongst others. rare. Other gems, such as garnet of both star and cat’s eye stones and include numerous long, thin Arguably, however, the most may display a four-rayed stars. are those that display a strong inclusions that run parallel to the valuable of the cat’s eye stones Cut is paramount in order to body colour as the presence of the base of the stone. are chrysoberyls, which range in produce a good cat’s eye or star many lighter-coloured inclusions Star stones – or, gemmologically colour from a very light yellow stone. In an ideal world, these –necessary to produce the speaking, stones that display through to the more desirable stones would be cut with little phenomenon – tends to weaken asterism – are similar to cat’s golden yellow and honey colours. or no excess material below the the body colour. Gemmological eye stones in that they rely The most valuable cat’s eye girdle, although this is rarely the testing is desirable for stones that on numerous inclusions being chrysoberyls are those that display case as the cutter tries to preserve display a strong star or cat’s eye, orientated so that a star pattern the so-called “milk and honey” weight to make extra dollars. as well as strong colour, as there is reflected back to the viewer. effect – light on one side of the eye For the jeweller, they must make are many synthetic and treated These stones too must be cut as and dark on the other – with such adequate compensation for the stones on the market. cabochons in order to properly stones potentially commanding heavy bottom so that the stone To view and sell a star or display the effect. prices in the thousands per carat. doesn’t roll in the setting. cat’s eye stone, one requires a Facetting either a cat’s eye or Asterism is also found in In many cases, the eye or direct incandescent light source. star stone would result in light numerous gem families, including the star is not aligned correctly Fluorescent light diffuses the light being reflected incorrectly off the many of those listed above, when cutting and sits off centre, being reflected off the inclusions inclusions and the effects of each but is perhaps most commonly requiring re-cutting. Stones where and the effect is lost – this is would be lost. encountered in the market in the dome of the cabochon is too something that business owners Historically the term cat’s the corundum group. Due to the flat will diffuse light and the eye, or should ask their staff to explain to eye referred only to the golden physical characteristics of the star, will only be visible looking at customers during a sale t 2 Jeweller / September 2010.

Load more