As you probably know, gemstones can come in essentially every color of the rainbow. The color of the gemstone is considered to be one of its core characteristics and is one of the most important aspects when determining the value and beauty of a gemstone. When choosing a gemstone's color it is important to examine the hue, tone and saturation of the stone.
Hue refers to the gradient or variety of a color in a stone. You may be surprised that one gem variety can have a variety of hues. For example the sapphire not only comes in the traditional blue that you think of when you hear the word sapphire, but it can also come in a range of other colors including slightly pink, purple, yellow, orange and green. The hue of a gemstone can greatly impact its value. Some gemstone colors, specifically hues like slightly purplish blue or slightly pinkish orange, are more sought after than others.
Tone refers to the relative lightness or darkness of a color. Tone is usually used to describe the intensity of the color which can range from nearly clear to dark and almost opaque. When light, dark, darkish or other adjectives to our color descriptions, we are referring to the tone of the color being described. For example, the most valued green color is a “grassy” green. Typical light pale lime or dark hunter greens are not as valued and will be less expensive. Of course color is a personal preference and just because a color isn’t as highly sought after does not mean that it will not appear beautiful and unique to you.
Saturation refers to the relative intensity of a color, ranging from weak to vivid. A gemstone with excellent saturation will reflect a pure vibrant color without any grey or brownish hues. Top valued gemstones are rated with either an excellent or very good saturation giving the stone a vibrant deep color.
Clarity is another important factor when determining the value of a gemstone. Clarity is a stone's relative freedom of tiny internal characteristics known as inclusions. Inclusions form while the stone is forming deep in the earth. You can think of these inclusions as the fingerprints or birthmarks of the stone and can help in the stone's identification. Generally gemstones with very few or small inclusions that are not visible to the naked are considered to be more valuable than stone with larger and more visible inclusions. While some stones like aquamarine and rubies are valued for their lack of inclusions, some stones such as cat’s-eye chrysoberyl and star sapphires, inclusions give the stone an extra phenomenal effect and add value. Some stones, including emeralds and red tourmaline, almost always have some eye visible inclusions and because of their rich color, a lack in clarity can detract less from their value than other stones which tend to be naturally freer of inclusions.
Gemstones, in their roughest form, come in a variety of appearances and quality. Some come in beautiful rich colors with no surface or very few inclusions, but most gemstones require some form of enhancement beyond cutting and polishing to make it attractive and appealing to the human eye. Gemstones are treated for many different reasons and many different ways. The most common treatments for gemstones are heating, infusion, bleaching & dying.
The heating of gemstones is one of the oldest and widespread enhancements. Almost 95% of corundum and all tanzanite are heated. Other gems such as topaz, aquamarine and amber are also commonly heated. Heating can cause different effects in different types of stones and can improve both the clarity and color of a stone.
Infusion or fracture filling of gems is also a centuries old practice. Infusion is the process of filling a gem with oil, resin, wax, glass or other material to improve the clarity of a stone. Infusion with oil is a regular treatment for emeralds and some rubies and sapphires to greatly improve their naked eye appearance.
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