The color of a gemstone is the most defining characteristic. When looking at a stone’s color you need to keep in mind the hue, saturation and tone.
Hue – The term “hue” refers to what most people think of when they hear the word “color.” There are six primary hues, known as violet, blue, green, yellow, orange and red. Between these colors are secondary colors such as yellow-orange or red-violet, with some stones containing multiple shades. The most valuable gemstones are ones that have primary hues as their dominant color.
Saturation – Also known as chroma, saturation is the most important factor in gemstone color grading. “Saturation” refers to the measurement of purity or intensity of a hue. A color which is highly saturated will contain a very narrow set of light wavelengths; this will make the color appear more pronounced than a similar stone that has a less saturated color.
Tone – This word refers to the degree of lightness in a stone, making a jewel seem clear, black or in between. The terms words light, medium or dark may be used alongside the name of a gemstone to indicate tone. Jewels which have medium lighting are more desirable than stones which have pale or dark tones.
Clarity refers to the amount of internal flaws or external blemishes that a gem has. Gemstone lucency grade is based on the number and visibility of inclusions. Unlike the similar rating for diamonds, the clarity classifications of gemstones are not standardized within the jewel industry. The range of clearness for gemstones is grouped into three types, which are:
Type I – gemstones are eye-clean, meaning the blemishes are not visible to the naked eye.
Type II – shows some flaws which are visible to the naked eye, but do not affect the overall beauty of the stone.
Type III – Gemstones which fall under this criterion almost always have eye-visible inclusions.
As colored gemstones come from a host of different sources, atomic compositions and molecular structures, each kind possesses different optical properties. Unlike diamonds, gemstones fall mainly under two cuts, faceted or non-faceted.
Faceted stones have a series of geometric flat panes cut onto the jewel’s surface, creating a sparkling effect. Like diamonds, these gemstones usually have a table, crown, girdle and culet. Non –faceted stones are cut in a way which produces a smooth surface, such as a cabochon cut, which usually has a rounded or squarish domed top and a flat bottom.
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