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Evaluating Gemstone Color

Gemstone colors can be amazing, yet most people are unable to explain why we see these rich, vibrant hues.

By Christopher Clark, GG, FGA, ASG, Gemologist & Co-Editor of The Sisk Gemology Reference | JTV
Published: 04/01/2011
Modified: 10/01/2020
gemstone-color gemstone-color-treatments colored-gems
Evaluating Gemstone Color
Table of Contents
  • Gemstone Color and the Eye of the Beholder
  • Light Absorption in Gemstone Color
  • Dominant and Secondary Colors in Gemstones
  • Gemstone Color Intensity
  • Gemstone Color Treatments and Enhancements
  • Identifying Colored Gemstones For Yourself

Have you ever seen a vivid blue diamond, or possibly a radiant pink sapphire? Gemstone colors can be amazing, yet most people are unable to explain why we see these rich, vibrant hues. In effect, what we perceive is the total effect of the residual light from the object we are viewing.

Our perception of color is due in part to three basic factors: the object itself, the type of light in which the object is viewed and our eyes.

emerald gold earrings, emerald silver tennis bracelet, gold emerald
ring, emerald gemstones
Emerald Jewelry

Gemstone Color and the Eye of the Beholder

Most of us know that light is composed of all the colors of the rainbow, as evidenced by nature's spectacular display after a rainstorm. Our eye is the real key to this phenomenon.

In an individual with normal sight, there is a series of rod- and cone-like structures spread out over a light sensitive membrane called the retina. Of the two, the cones determine our visual acuity and sensitivity to color. It is believed that there are three varieties of cones; each sensitive to a different range of the total white light spectrum. In the case of color blindness, one or more of these receptors is either defective or nonfunctional.

How Gemstones Get Their Color (source: Gemstones.com YouTube)

Light Absorption in Gemstone Color

In a simple case like a piece of red glass, nearly all the blue, green and yellow rays are absorbed, while the red rays are freely transmitted. Therefore, we see the color red. Simple, right? With gemstone colors, there is a much higher level of complexity.

Light hitting a gemstone may be reflected and dispersed internally. In addition, some wavelengths of white light may interact with the atomic structure of the stone, changing its state and altering what is absorbed and emitted. Sometimes inclusions may interfere with the light entering the gem and cause it to become scattered or diffracted. In many stones, a combination of factors may be responsible for the gemstone colors we ultimately perceive.

How Do Gems Get Their Color? (source: Gemstones.com YouTube)

Dominant and Secondary Colors in Gemstones

If your gem is ROYGBV (red-orange-yellow-green-blue-violet) then it’s easy to identify the gemstone’s color, but what if it’s somewhere in between? After all, gemstones can occur in every imaginable color across a vast variety of types. Few gemstones exhibit pure hues and those that do are highly prized.

Even gemstones such as ruby, a color gemstone renowned for some of the finest reds in nature, will have secondary colors. Ruby quite often shows as orangeish or purple-red.

When gemstones exhibit multiple colors, one color is often dominant. In this case, we state the modifying color first and the dominant gemstone color last. For example, most aquamarine, a blue variety of beryl, show a greenish blue color. If both colors are equal, we would state the gemstone color is blue-green or green-blue to show they are present in equal quantity.

When identifying or grading the color of gemstones, it is best to use only the color names and avoid using descriptors like royal, cornflower, lemon or pigeon’s blood as these words all refer to a range of gemstone colors rather than a specific hue.

It is best to use only the color names and avoid using descriptors... as these words all refer to a range of gemstone colors rather than a specific hue.

Gemstone Color Intensity

Some gemstone colors may also be modified by using the terms grayish or brownish before the color. These adjectives are describing the intensity of the hue such as how strong or weak the color is. Cool colors such as green, blue and violet will tend to be grayish when their saturation is less than moderately strong. Likewise, warm colors such as purple, red, orange and yellow will tend to be brownish when they have a less than moderate saturation.

With a stronger than moderate saturation, gemstone colors are usually described as strong, intense or vivid. Often colors will also be referred to as light or dark to describe the tone. Very light or very dark gemstones will also tend to have a lower saturation and appear grayish or brownish.

bi-color emerald cut watermelon tourmaline and pink brilliant cut gemstone
Bi-Color Tourmaline

Gemstone Color Treatments and Enhancements

Enhancing and improving the colors of a gemstone is possible through several means. Heat treatment, radiation, oiling and filling are the three primary means through which gemstones get enhanced colors. A large percentage of gemstones on the market are treated in some way or another, in order to help the color, clarity and even the durability of a gemstone. Gemstones that are treated are often natural stones, which receive enhancements through these processes, and are then sold to jewelers and gemstone collectors.

Common gemstones to receive treatment include members of the corundum family such as sapphire and ruby, blue topaz, green diamond, tanzanite and many more. Heat treatments in corundum can enhance the color of the stone, as well as adding or removing asterisms, a star-shaped inclusion, in the gemstone. Combining heat and oiling treatments can magnify the deep green color of an emerald. Enhancement via radiation opens up a world of new possibilities for colors. Blue topaz is rarely found because it needs radiation in order to achieve its coloration. Thankfully, laboratories can manually introduce whatever a preexisting gemstone needs to complete its color transformation. Some lab-heated gemstones, such as tanzanite, are near impossible to distinguish from naturally occurring violet-blue tanzanite.

Gem Treatments: A Close Up Look (source: Gemstones.com YouTube)

Identifying Colored Gemstones For Yourself

Now, take a look around you or a go grab a tray of your favorite gemstones and have fun naming all the colors you see. So the next time you see a vibrant color gemstone, marvel at nature's amazing gift to the human race. The beauty of a gemstone is more than skin deep and considerably more complex.

More Gemstone Articles

article

Gemstone Dispersion

Dispersion is the display of color in a gemstone and may be classified as not observable, moderate, strong or very strong.
Gemstone Dispersion
article

Optical Properties

Learn the optical properties of gemstones including play of color, star and cat's eye.
Optical Properties
article

Gemstone Transparency

Determining whether your gemstone is transparent, translucent or opaque will help you catalogue your gemstones.
Gemstone Transparency
article

Gemstone Luster

When it comes to describing a gemstone’s appearance, luster refers to how a gem’s surface looks when it reflects light.
Gemstone Luster
Christopher Clark

About the author

Christopher Clark

A Graduate Gemologist and Fellow of the Gemological Association of Great Britain, Christopher has spent the last 4 years co-editing The Sisk Gemology Reference. He also acts as a customer advocate by inspecting and testing gemstones as they come into Jewelry Television to ensure they are exactly what our customers expect. He is an avid collector of vintage jewelry, gemstones, mineral specimens and spheres. Employed at Jewelry Television since 2006, Christopher spends much of his time immersed in the fascinating world of jewelry and gemstones.

Christopher’s passion for collecting valuables and precious stones began when he was shopping at a retired jeweler’s garage sale and he purchased a parcel of colored gemstones and a “lump of metal” that turned out to be GOLD! From that moment forward, the treasure hunt was on! But occasionally, he does become a commodities trader as he keeps an ever-watchful eye on precious metal prices. Unfortunately for his wallet, though, most of the treasures he acquires are never resold as they simply get added to his ever-growing collections. Christopher especially enjoys collecting vintage pocket watches and Mexican antique silver jewelry.

Christopher is now an Accredited Senior Gemologist with the Accredited Gemologists Association. He volunteers his time with a local gemological society for identifying gemstones. Christopher is always excited to attend major gemstone trade shows and is always on the look-out for the next great gem to bring JTV customers. Working closely with our vendors, Christopher has built a business rapport with them that allows for an easy trust and mutually beneficial working relationship. His favorite gem? Without a doubt, OPAL!

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