Color is typically the most important value-setting factor for gemstones. All gems have a preferred color or a relatively small range of preferred colors. The more the color varies from this range, whether lighter or darker, more or less vivid, the less valuable the stone. We like to think of candy, especially Jolly Rancher's, when we think of the best colors for gemstones! If you can image how a gem would taste, that is the color you want. A watermelon-flavored spinel, an an apple-flavored tsavorite, a cherry ruby... you get it.
Clarity Type I stones usually form free of clarity characteristics. These gemstones include diamond, aquamarine, green tourmaline, and tanzanite. These gems are usually free from inclusions to the unaided eye.
Clarity Type II stones normally contain clarity characteristics. These gemstones include sapphire, amethyst, peridot and ruby. These gems typically show some eye-visible inclusions that do not detract from their overall beauty.
Clarity Type III stones almost always contain clarity characteristics. These gemstones include emerald and pink tourmaline. Although these gems almost always contain inclusions that one can easily see, they are part of the stone's unique chracter and in the case of an emerald have a name. The beauiful internal qualities of an emerald are called le jardin, the garden in the emerald.
The clarity grades that one may be familiar with in the diamond scale are then applied to the colored stone. And although the nomenclature is familiar, the scale is changed for each clarity type. For instance, a slightly included (SI) graded Type I gemstone will have a much different appearance than a SI Type III gemstone. The first will contain minute inclusions that would be difficult to see with the unaided eye and the latter will have noticeable inclusions that are readily apparent to the unaided eye.
Cut refers to the shape or design of a stone as well as the precision of the stone's proportions and finish. The cutting process revelas the beauty of a gem. Colored stones are cut into the usual shapes that one is familiar with like round, oval, and emerald cut that can also be carved and fashioned into fantasy shapes...limited only by a cutter's imagination.
The proportions of a gemstone involve the balance and appeal of a given design. The finish refers to the perfection of the workmanship. A well-proportioned gem will show off the stone's optical properties to its fullest potential.
When all other factors of a gem are even (color, clarity and weight), a well-cut stone will be move valuable.