Assessing Colored Gemstones, Part 4 - Cut

In this final part of our JET Team discussion about assessing fine colored gemstones, we look at the importance of cut in grading the stones. All gemstone images are courtesy of Heritage Auctions.

Cut refers to the manner in which a stone has been cut - such as emerald-cut, step-cut, brilliant-cut - rather than to its overall shape. The skill of the cutter is demonstrated by the quality of cut, which can have a big impact on the overall color. Thus the way a stone is cut not only determines the final beauty and brilliance of that gemstone, it also affects its grade and value.

From left: Very good oval pink spinel, 5.97ct
Very good enhanced octagonal emerald, 4ct
Good oval blue zircon, 6.32ct

The most important factors here are the proportions and symmetry of the cut, and the way a stone has been polished. The cut should be neither too shallow nor too deep, and there should be a sharp and well-defined difference between the top part, or crown, of the gemstone and the lower part, or pavillion. For the highest grade the facets should be expertly cut and well-proportioned, and should be polished so that the finished gemstone reflects and transmits light evenly, giving it a bright and glittery brilliance.

From left: Very good oval golden beryl, 60.50ct
Excellent octagonal step-cut natural sapphire, 20.21ct
Excellent oval natural yellow-green tourmaline, 4.89ct

With pearls, lustre is what gives them their pearly quality, and is the way they reflect and diffuse light. Thus more lustrous pearls will be graded higher than less lustrous examples. Unlike other colored gemstones, pearls are also graded according to their shape and size. So, for example, round pearls should be as close as possible to perfectly round with the naked eye. Natural, saltwater pearls are valued much more highly than cultured pearls, while freshwater pearls are generally less valuable.

From left: Very good enhanced pear-shaped paraiba tourmaline, 1.24 ctExcellent oval-shaped pink sapphire, 2.54ctVery good natural saltwater conch pearl, 6.40ct

We hope you've found this discussion helpful! If you're considering purchasing colored gemstones, Gemfields has a useful online Buyer’s Guide.