The Basics
As with diamonds, gemstone quality and value are evaluated according to the "Four Cs": color, clarity, cut, and carat weight. And
there's one other, much less scientific factor--perception.
Color, not surprisingly, is the key factor. A common misperception in judging gems
is people assume that the darker the color, the better the stone. That isn't true:
color can be too dark, as with some sapphires that look more black than blue. If
a gem's color is too dark, it is subdued and lifeless. A much better rule of thumb
is the brighter and more rich and vivid the color the better. In general, within
each gemstone variety, a clear, medium-tone, very intense and saturated basic color
is the most preferred. Muted colors or colors between hues, which some might find
very attractive, are usually less expensive. Look at the color in different kinds
of light, since the light spectrum can affect color greatly.
The next most important factor affecting value is clarity, with clear transparent
gemstones with no visible flaws being the most valued. Some gemstone varieties,
notably emerald and red tourmaline, are very rare without inclusions of some kind
so the price structure takes this into account. Other gems are actually valued for
their inclusions! Tiny inclusions reflecting back light put the eye in cat's-eye
chrysoberyl and the star in star sapphire and ruby. Inclusions can also act as a
birthmark, telling where a particular gemstone was mined.
A good cut is something that may not cost more but can add or subtract a lot of
beauty. A well-cut faceted gemstone reflects light back evenly across its surface
area when held face up. If the stone is too deep and narrow, areas will be dark.
If it is too shallow and wide, parts of the stone will be washed out and lifeless.
Gemstones are generally sold by weight not by size. Some gems are denser than others
so the same weight stone may be a different size! The carat weight also affects
the price--large gemstones are usually more rare, so the price per carat is higher.
