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Colored Gemstone Buying Guide: The 4 Cs of Colored Gems






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Jewelry and gems
The Buying Guide

Colored Gemstones

Determining value in colored gems

Color is the most important determinant of value in color gems.  It is also, too often, the principal determinant in erroneous identification because, unfortunately, most people don’t realize how many gems look alike in color.  And even professionals in the trade can be misled or caught of-guard.  Too often recognition and identification are based on color alone because so few jewelers and customers are aware of the large number of similarly colored stones that are available.
Until recently, the gemstone industry has promoted very few colored stones, concentrating instead on the more precious and profitable gems. But growing popularity of colored stones has expanded the market so that consumers now find they have a choice.  If you want an emerald green stone but cannot afford a fine emerald, you might choose a green garnet (tsavorite), a green or “chrome” tourmaline, or perhaps green “tanzanite” (tanzanite is the blue variety of zoisite; now there is a green variety, which is sometimes called green tanzanite).  And these are at least four gem materials from which to choose, no matter what color you prefer. New gems are being discovered each year, and known gems are being discovered in new colors.  Increasingly, fine jewelers and designers are creating exciting pieces using the full color spectrum.

The four Cs of colored gems

We have already discussed the four Cs to consider in choosing a diamond, but colored gems have Four Cs of their own: color, color, color, and color!  This statement may sound like an exaggeration, but not so much as you might think.  Generally speaking, the finer and rarer the color, the less impact cutting, clarity, and carat weight have on the value of the gem.  On the other hand, the more common the color, the more impact these other factors have.
When we discuss color, we are not talking simply about hue.  Color science, and the evaluation of color, is a very complex area. But if you understand the various elements that must be factored into the evaluation of color, you can begin to look at colored gems in a totally different light.
Color is affected by many variables that make it difficult to evaluate precisely.  Perhaps the most significant factor is light; the type of light and its intensity can affect color dramatically. In addition, color can be very subjective in terms of what is considered pleasing and desirable. Nonetheless, there has been extensive research and development in the field of color science, and experts are working to develop a viable color grading system.  Gemologist at the GIA have produced a machine called Color Master, a type of visual color-meter, around which they have developed a color grading system that is gaining increasing acceptance.  American Gemologist Laboratories has continued to develop its ColorScan system, and several other systems are gaining acceptance, one of the most promising newcomers being Howard Rubin’s GemDialodgue.  Most gem pricing guides use at least one of these systems to describes the quality of the stones they are pricing, but problems still exist with color communication, and no solution seems imminent, and no system has yet replaced the ages old eye and brain combination, coupled with years of experience in the colored gemstone field.

The key elements in describing color

The color we see in gems is always some combination of pure spectral colors, which range from pure red to pure violet, coupled with varying degrees of brown, white, black, and gray.  It is these later colors, in combination with spectral colors, that affect the tone of the color seen and that make the classification of color so difficult. For example, if white is present with red, you will have a lighter tone or shade of red; if black is present, a darker tone or shade.  Depending upon the degree of gray, white, black, or brown an almost infinite number of color combinations can result.
As a general rule, the closer a stone’s color is to the pure spectral hue, the better the color is considered to be; the closer it comes to a pure hue, the rarer and more valuable.  For example, if we are considering a green stone, the purer the green, the better the color. In other words, the closer it comes to being a pure spectral green, having no undertone (tint) of any color such as blue or yellow, the better the color.  There is no such thing in nature, however, as a perfectly pure color; color is always modified by an undertone of another hue.  But these undertones can create very beautiful, unusual, distinctive colors that are often very desirable.

In describing color, it is often refer to these factors:

  • Hue: The precise spectral color (red, orange, yellow, green, blue, violet, indigo)
  • Intensity (or saturation): The brightness or vividness (or dullness or drabness) of the color
  • Tone:  How much black, white, gray, or brown, is present (how light or dark the stone is)
  • Distribution:  The even (or uneven) distribution of color

Both intensity and tone of color can be significantly affected by the proportioning of the cut.  In other words, a good lapidary (stone cutter) working with a fine stone will be able to bring out its inherent, potential beauty to the fullest, increasing the gem’s desirability.  A poor cutter may take the same rough material and create a stone that is not really pleasing, because the cut can significantly reduce the vividness and alter the depth of color, usually producing a stone is much too dark to be attractive, or one in which the color seems washed out or watery.
In general, stones that are either very light (pale) or very dark sell for less per carat. There seems to be a common belief that the darker the stone, the better.  This is true to a point.  A rich, deep color is desirable, but not a depth of color that approaches black.  The average consumer must shop around and train the eye to distinguish between a nice depth of color and a stone that is too dark.
As a general rule, it is even more important to shop around when considering colored gemstones than it is when buying diamonds.  You must develop an eye for all the variables of color; hue, intensity, tone, and distribution.  Some stones simply exhibit a more intense, vivid color than other stones (all being equal), but only by extensive visual comparison can you develop your eye to perceive differences and make reliable judgment.
For example, let’s discuss the variations among rubies for a moment. The finest red rubies are Burmese. While they are not a pure red, these are the closest to pure. The tone may vary, however, from very light to very dark.  As with most stones, the very light to very dark.  As with most stones, the very light stones and very dark sell for less per carat. Burmese rubies are the most highly prized and the most expensive, because of desirability of their color and their scarcity. They also exhibit a beautiful red in all light, while rubies from other locations may exhibit a lovely red only in incandescent light ( such as you find in candlelight, lamplight, chandeliers, and most evening light) and become pinkish or purplish when seen in fluorescent light.
Thai rubies can vary tremendously in hue and tone, going from a light to a dark red varying degrees of a bluish undertone, giving them a purplish cast and making them look like the much cheaper reddish purple gemstone, the garnet. While some Thai rubies can have very fine color rivaling the Burmese (these are very expensive), most Thai stones are much less expensive than the Burmese, primarily because the color can’t compare.
African rubies from Tanzania usually have a tint or undertone of brown or orange, which makes them also much cheaper than the Burmese reds, but depending upon the precise shade, often more valuable than the Thai ruby, depending on the lather’s color. Rubies from newly discovered deposits in Kenya, Cambodia, Vietnam, and parts of China are very close in hue and tone to Burmese, and may also retain their color in all light. These stones can command very high prices if other quality factors are fine.
Ceylon, rubies are also encountered with relative frequency. However, these are usually so pale that in the United States they would called “pink sapphire” rather than ruby since the tone is consistently so light. The saturation of color is too weak to be technically described as ruby, since ruby should be red, not pink. You should be aware that in the United States, the color must be deep enough to be considered red to be called “ruby” while in other parts of the world, the name “ruby” may be applied if the stone falls anywhere in the pink to red range. It should be noted that sapphire and ruby are the same stone, physically and chemically.  The red variety is called ruby, while the equally popular blue is called sapphire.  Both belong to the “corundum” family.
Next, let’s look at the spectrum of emerald colors.  Some of the finest emeralds today come from Colombia and are the color of fresh, young green grass; an almost pure spectrum green with a faint tint of either yellow or blue.  The color found in the finest of these emeralds is unique to Colombia.  Unfortunately, very fine Colombian emeralds with exceptional color are extremely rare now, and thus very costly.
African emeralds can also exhibit a lovely shade of green, but with a bluer undertone, and a slightly dark tone, probably due to traces of iron, which may make the stone less desirable, and thus less valuable than a fine emerald from Colombia.  However, the African stones usually have fewer inclusions (flaws) than Colombian, and depending on depth of color, compare very favorably to the Colombian, aesthetically, while costing less per carat.

Light and environment affect the color you see

The color of a stone can be drastically affected by the kind of light and the environment in which the examination is being conducted; that is , variables as disparate as the color of wallpaper or the tint of a shirt can alter a stone’s appearance.  If examined under fluorescent light, a ruby may not show its fullest red, because most fluorescent lights are weak in red rays; this causes the red in the ruby to be diminished and to appear more as a purple red.  The same ruby examined in sunlight or incandescent light (an ordinary electric light bulb), neither of which is weak in red rays, will appear a truer, fuller red. Because the color of a ruby is dependent upon the “color temperature” or type of light used, it will always look best in warm light. A ruby looks even redder if examined against a piece of orange yellow paper.  For this reason, loose rubies are often shown in little envelopes, called “parcel papers,” that have a yellow orange inner paper liner to show the red color to the fullest.
Blue sapphire, another intensely colored gem, comes in numerous tones of blue; from light to very dark, some so dark that they look black in incandescent (warm) light.  Most sapphires, however, look bluest in fluorescent light, or day light.  Many contain some degree of green.  The more green, the lower the price.  Some even exhibit a change; we’ve seen blue sapphires that were a magnificent blue in daylight turn to an amethyst purple in incandescent light. Some, like the stones from the Umba Valley in Tanzania, turn slightly lavender over time.  The lighter blues are generally referred to as Ceylon colored sapphire; the finest and most expensive blue sapphires generally come from Burma (now called Myanmar) and Kashmir and exhibit a rich, true blue in all kinds of light.  Those from Kashmir exhibit a more subdued, soft velvety look comparison to Burmese or Ceylon types sapphires.
An environment that is beneficial to your gemstone can also be created by the setting in which the stone is mounted.  For example, an emerald cut emerald mounted in a normal four prong setting will not appear to have as deep a color as it will if mounted in a special box type setting that completely encloses the stone so that light is prevented from entering its sides. The “shadowing” effect created by this prevented from entering its sides.  The “shadowing” effect created by this type of enclosure deepens the color of the stone.  This technique, and other types of special mounting, can be used to improve the color of any colored gemstone where it is desirable to intensify the color.
Another example is found with a fine expensive imperial jade.  A fine jade cabochon (a smooth, rounded cut which has no facets) is often mounted with a solid rim around the girdle (bezel set), with the back of the ring constructed much deeper than the actual bottom of the stone, and the back side of the ring nearly completely closed except for a small opening at the bottom center. This is done either to hide a stone’s defect or to improve its body color.
Opal, too, is often set in ways that enhance color.  The environment in this case is a closed, flat backing which has been blackened to intensify the play of color (fire) seen in the stone.

A word about color distribution or zoning

Even though zoning doesn’t really describe color, and is sometimes evaluated as part of the “clarity” grade, we think it should be discussed as part of color evaluation.
In some stones the color is not always evenly distributed but exists in zones; in some stones the pattern created by altering ones of color and colorlessness resembles stripes.  Zoning is frequently observed in amethyst, ruby, and sapphire.  These zones are most easily seen if you look through the side of the stone and move it slowly, while tilting and rotating it.
Sometimes a stone in the rough is colorless, or nearly so, but has a spot or layer of color. If the cutter cuts the stone so that the culet is in the color spot, the whole stone will appear that color.  If there is a layer and the cutter cuts the stone so that the layer lies in a plane nearly parallel to the table, the whole stone will look completely colored.  Evenness of color and complete saturation of color are very important in determining the value of colored gems. Even though you may not notice the zones themselves when looking at the stone from the top, a heavily zoned stone will lack the color vibrance of another stone without such zoning. Normally, if the zoning isn’t noticeable from the top, value is not dramatically reduced, but a stone with even color will face up better and will cost more.  And, depending upon the hue and tone, possibly much more.

A word about “color change” gemstones

Some gemstones exhibit a very strange phenomenon when viewed in different types of light; they change color completely.  These stones are called “color-change” gems. There are color change spinels, color change sapphires, color change garnets, and so no. In these gem families, however, the color change phenomenon is rare. The gem alexandrite, on the other hand, always exhibits a color change, and its value is based largely upon degree of change.  There are even color change synthetics, such as the inexpensive synthetic color change sapphire that is often misrepresented and sold as genuine alexandrite.  Alexandrite is a bluish green gem in daylight or under daylight type fluorescent light, and a deep red or purple red under incandescent light.


As with diamonds, clarity refers to absence of internal flaws (inclusions) or external blemishesFlawless in colored gemstones is perhaps even rarer than diamonds.  However, while clarity is important, and the cleaner the stone the better, flawlessness in colored gemstones does not usually carry the premium that it does with diamonds. Light, pastel-colored stones will require better clarity because the flaws are more readily visible in these stones; in darker toned stones the flaws may not be as important a variable because they are masked by the depth of color.
The type and placement of flaws is a more important consideration in colored gemstones than the presence of flaws in and of themselves.  For example, a large crack (feather) that is very close to the surface of a stone; especially on the top, might be dangerous because it weakens the stone’s durability. It may also break the light continuity, and may show an iridescent effect as well. Iridescence usually means that a fracture or feather breaks through the surface somewhere on the stone.  Such a flaw would detract from the stone’s beauty and certainly reduce its value.  But if the fracture is small and positioned in an unobtrusive part of the stone, it will have minimal effect on durability, beauty, or value.  Some flaws actually help a gemologist or jeweler to identify a stone, since certain types of flaws are characteristic of specific gems and specific localities. In some cases the presence of a particular flaw may provide positive identification of the exact variety or origin and actually cause an increase in the per carat value.  We should note, however, that a very fine colored gem that really is flawless will probably bring a disproportionately much higher price per carat because it is so rare.  Because they are so rare, flawless rubies, sapphires, emeralds, and so on should always be viewed with suspicion; have their genuineness verified by a gem testing lab.  The more new synthetic gems are often flawless, and easy to confuse with genuine, natural gems.
If the flaws weaken the stone’s durability, affect color, are easily noticeable, or are too numerous, they will significantly reduce price. Otherwise, they may not adversely affect price, and in some cases, if they provide positive identification and proof of origin, they may actually increase the cost rather than reduce it, as with Burmese rubies and Colombian emeralds.
Again, it is important to shop around and becomes familiar with the gemstone you wish to purchase and to train your eye to discern what is “normal” so you can decide what is acceptable or objectionable.

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To Web Masters:

The article above can be used on your web site or newsletter.

When it is published, May I request that you include my name and resource box (the bio., contact and copyright information that follows the article.  I would also appreciate if you could send me an e-mail of notification along with a complimentary copy of publication.

Bijan Aziz is the owner and Web Master for The Jewelry Hut.

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