Colored Stones
What are the factors that influence price on colored gemstones? How do I know that I am investing in a valuable colored stone?
The factor that will most affect the value of the stone is color.
Because gem color descriptions are so varied and subject to individual perception, GIA developed the Colored Stone Grading System. It helps judge a stone’s color from the most preferred to the least preferred available for its specific species.
A. Color
The first thing to look at is color. Color is composed of Tone, Hue & Saturation. Tone is the degree of darkness or lightness of a color (this ranges from 2- very light to 7 - very dark.
This is the first thing we look at when describing a gem’s color. The gem should fall into the 5-6 category (medium to medium dark).
Hue is the first impression you get of a gem’s basic color. The GIA system uses 31 names to describe the color.
Emeralds: The most preferred emerald hues should fall between the bluish green (bG) to green (G) category.
Sapphire: The most preffered sapphire hues should fall between velvety blue to violetish blue (vB).
Rubies: The most preferred ruby hues should have a pure vibrant red (R) to a slightly purplish red hue (slpR).
Saturation:
Saturation is the color’s strength or intensity. Its assesed on a six-level scale (1-6). If the hue has any brownish or grayish components, saturation is 3 or lower. If brown or gray appear distinctly, saturation is 1 or 2. If you can only see a slight hint of brown or gray, then saturation will be 3. If you can see no trace of gray or brown, saturation is 4 or higher. All other things equal, a saturation of 4-6 would ideally be the categeory that your gem should fall into, 6 being the most valuable saturation level.
Sapphire example: 1 (left) would be grayish, the second
one would be slightly grayish (2), the third would be very
slightly grayish (3), the fourth would be moderately strong (4),
the fifth would be strong (5) and the last one would be
considered vivid (6).
Medium to medium-dark tones and strongly to vividly saturated color in a gem indicates high value. Gems with these properties deserve more of your time and attention
B. Cut:
The beauty of a stone’s cut comes from a combination of brilliance, proportion and finish. The brilliance grade is an estimate of the percentage of light return for the gem’s face up area. Symmetry and dimensions need to be taken into account in order to judge propotions effectively.
The original spinel (left) has no brilliance, the refinished spinel (right) has a greatly
improved brilliance, symmetry and face - up color which will eventually result in a
higher sale price.
Flat or shallow pavilions usually result in lower quality intensity - called window. On stones with deep pavilions, you will usually see dark areas or extinction through the stone’s crown.
The stone on the right is cut too shallow, light passes through
instead of returning to the eye. The stone on the left returns
the light as brilliance.
All things equal, the pink sapphire on the left will be the
most valuable because it displays the highest percentage
of brilliance.
High brilliance in a stone indicates good symmetry and proportions. Lack of face-up brilliance indicates symmetry and profile problems. Uneven brilliance through the crown may occur due to pavillion symmetry problems. Low brilliance usually tells you the pavillion is too shallow or too deep. Poor cutting and surface polish indicate low value in a stone.
C. Clarity:
Prominent, distracting, eye-visible inclusions usually reduce a gem’s value. Clarity characteristics that affect transparency, brilliance, or durability have the most influence on value.
This sapphire has numerous inclusions
that impair its transparency and value.
Because of the way some types of gems form, they tend to contain more inclusions than others. For example, emeralds are typically much more included than aquamarines, so dealers tend to be much less critical of faceted emeralds with eye-visible inclusions than they are of aquamarines of similar clarity.
Emeralds are classified as Type III
stones because they usually contain
an abundance of inclusions.
D. Carat Weight:
Large gems that are similar in overall quality to smaller ones of the same species usually cost more because the rough required to cut them is more rare. Small stones are generally more available than larger ones, and therefore are less expensive.
was presented at auction by Christie’s in Geneva
and was bought for $17,300,000
There are other factors that affect the value of the stone such as location or country of origin. For many colored gems, the country of origin or mining location greatly affects the value. In sapphires, that is the case for Kashimir blue sapphires that are worth far more than a similar sapphire mined elsewhere.
Politics and changes of government in producer countries can have a drastic effect on a gem production and thus supply. This will drastically affect its availability and price.
Lastly, the lack of treatment in a gemstone will generally be more valuable than a treated gemstone. Ex: For fine quality sapphires, confirmation from an independent lab like GIA that there is no evidence of heat adds to a sapphire’s rarity and value.