Color Gemstone Grading

While diamonds and colored gemstones are very popular, few understand how they are graded. People may be more familiar with the concept of diamond grading, if they’ve gotten engaged or made another large diamond purchase, but oftentimes the grading of color gemstones is overlooked.

If you don’t own  color gemstones or haven’t read much about them, you might assume that color gemstones are comparable to each other, but the truth is that they have a complicated grading structure and they can all vary significantly from one another.

Gemstones have been receiving grades since ancient times in places like Egypt and Greece, where gemstones were considered to be very rare and only able to be owned by the very wealthy. At that time (and still sometimes now), color gemstones were thought to have magical qualities that could ward off evil or bring affluence if used in the right ways. Although they didn’t have detailed grading scales in ancient times, they instead judged the stones on their color and how difficult they were to own. Similar to modern times, demand influenced pricing, and if a color gemstone had a vibrant color and was not common, it was in higher demand and therefore came at a higher price.

During the Renaissance era, gemstones became more of a topic to be studied by scholars, and they began writing books on them, such as "De Lapidibus" by Theophrastus and "Book of Stones" by Albertus Magnus. In the 17th century, gemology emerged as a field of study and scientists began doing experiments to learn more about gemstones and document their findings. Later, Carl Linnaeus developed the first real system to classify color gemstones based on their properties, which was the foundation for the modern grading scale. In the 20th century, The Gemological Institute of America (GIA) was founded and they first introduced their standard grading scale for diamonds, still known today as the 4Cs (cut, color, clarity, and carat weight).

With the advancement of technology and new instruments capable of measuring more details about the composition of color gemstones, the 4Cs system was eventually adapted to be used for the grading of color gemstones as well. Gemologists today have a great deal of technology on their side when it comes to grading color gemstones. Spectroscopes, spectrophotometers, microscopes, loupes, and ultraviolet lamps are just a few, but details on each individual instrument would be a lesson for another day!

Rest assured that gemologists use all the tools at their disposal to properly grade color gemstones in order to make sure that consumers are well informed of what they are purchasing. During the grading process, they evaluate the following aspects of the gemstone:

Color: Usually considered to be the most important aspect of a gemstone, color is evaluated first and will significantly affect the value of the gemstone. When evaluating the color, gemologists look at how vibrant the color is, and they use three characteristics for this: hue, tone, and saturation. The hue is the general color that you see right away when looking at the stone (such as blue or green). The tone is how light or dark the color is, while the saturation refers to how intense the color is. Gemstones that are graded with vivid and saturated colors are more valuable because they are more rare.

Clarity: Gemstone clarity is ultimately determined based on the inclusions that are visible in the stone and at what magnification they are visible. Because gemstones are formed deep within the earth, different elements can become trapped within the stone, forming imperfections within the stone that are referred to as inclusions. The gemstone is assigned a clarity grade based on the existence, size, quantity, and visibility of inclusions. The larger an inclusion is–or a high number of inclusions–will decrease the clarity grade assigned to the gemstone. The location of the inclusion can also decrease the clarity grade. For example, if an inclusion is located near the edge of a gemstone and can be covered with a prong, it would receive a higher clarity grade than a gemstone with an inclusion located in the center of the stone, which would be nearly impossible to hide. The type of inclusion can also affect the clarity grade. Certain types of inclusions are less noticeable or more clear than others, so would not affect the grade as much as darker or more visible inclusions.

Cut: The cut of a gemstone is one of the most important factors because it determines how light is able to pass through the stone and return to your eye, giving the stone the ability to sparkle. Cut is determined by the proportions, symmetry, and polish of the individual facets, but each type of gemstone (and their shape) requires a different cut to maximize the light return.

Carat Weight: Carat weight is a measure of size. In most circumstances larger stones are more expensive, though the combination of all grading aspects will affect the price.

Origin: The location where a stone was mined can affect the value since certain mines are known for producing exceptional stones.

Treatment: Whether or not a stone has undergone any treatment to enhance the color or clarity can also influence the value. While there’s nothing wrong with these treatments in general, many people consider treated stones to no longer be natural, which reduces the value of them significantly.

Color Changing Gemstones

Color can be a tricky aspect of grading some gemstones because there are some gemstones that are color changing, depending upon their light source. They are quite rare and beautiful, so let’s examine a few of those gemstones now.

Alexandrite: Alexandrite is the most well known color changing gemstone and was first discovered in Russia in the 1830s. In daylight, alexandrites look blue-green in color, but under incandescent light, they look red-purple. The color change in alexandrite is because of the chromium within the crystals of the stone. Natural alexandrite is rare and can fetch a very high price tag, but the lab grown alternatives are more affordable and readily available.

Color Change Sapphire: While there are almost endless color options for sapphires, there are also color changing sapphires. They appear blue in daylight and red or purple in incandescent light.

Garnet: Garnet is another gemstone that is available in a variety of colors, including color changing varieties. The different hues of a color change garnet can vary depending upon the type of garnet, and their change may not be as obvious as the alexandrite, but still visible and beautiful.

Hopefully now it’s a bit more clear that color gemstones have a complex grading system and that many aspects are taken into account when determining their value. Though the grading practices have evolved throughout the course of history, as technological advancements have become more readily available, it’s held true that the more vibrant and rare gemstones fetch a higher price. Not all gemstones come with a grading certificate, but if you’re making a significant purchase, don’t hesitate to ask your jeweler for a certified stone so you can see firsthand the factors that contribute to the stone’s value.