For gemstones, the 4C's for determining quality is derived and modified from the evaluation of diamonds. The color, the carat weight, the cut, and the clarity together form decisive factors in the quality and therefore the value of a sapphire. When evaluating and buying a sapphire, the most important aspects are not only the 4Cs, but also the 'Country of Origin' of the gemstone, so it would be more accurate to say the 5Cs.
Unlike the universal grading system for diamonds, in the case of a colored gemstone such as sapphire, color is a determining factor. One often reads that the color determines 70% of its value compared to the importance of location in real estate. However, to put a percentage is not enough, it is an interaction of the 5 quality criteria. The color, however, has a great influence on the quality determination, the value due to its rarity, and the beauty in the eye of the beholder. The color is a criterion that is worth looking at differentiated, especially with the sapphire, because this knowledge is important when buying a sapphire.
Color assessment can vary subjectively from person to person, and the light source can affect the appearance of the color in a sapphire. For decades, gemologists have been searching for a more universal and objective means of assessing color. The color of a sapphire can be divided into three categories: Hue, tone, and saturation. These parameters are used in conjunction with the determination of color and are also a criterion in determining the quality of a sapphire.
The first factor, hue, refers to the specific color of the stone. The base color of the gemstone. Many sapphires of one basic color have a combination of other hues. As an example, in the case of pink sapphire, a violet-pink hue, or in the case of blue sapphire, a greenish-blue hue. It is desirable with sapphire to have as pure a hue as possible. This means that secondary colors should either be absent or minimal, a pure pink or violet or a pure blue or green.
The second factor, tone, describes the level of color strength or saturation. The intensity of how light or dark the color of a stone also influences the value of a sapphire. The sapphire can be simply blue, but when differentiated, it can have a more light blue tone or a deep blue. Preferred hues for sapphires vary from hue to hue, but most fine sapphires have a medium to medium-dark hue. Sapphires that have a very dark hue, for example, are often referred to as 'inky'.
Lastly, Saturation describes how pure or intense a color appears and is a key component in determining the value of a sapphire. The color of sapphire can be 'diluted' with a so-called 'saturation modifier'. For cool colored sapphires such as blue, green, and purple, 'gray' is the usual saturation modifier. For warm-colored sapphires, including yellow, red, and orange, the typical saturation modifier is 'brown'. Sapphires with lower grayish or brownish saturation modifiers have a higher degree of saturation and appear more vivid in appearance to the viewer.
The hue of a stone can be a pure primary color (red, blue, or yellow) or a secondary color resulting from the mixing of primary colors (orange, green, and violet). The color of a stone can also be mixed with gray, white, or black, which requires further grading. If a stone is gray, the color saturation needs to be graded. If a stone is white, the color tint must be determined. The presence of black in a stone can affect the hue. Most stones are more valuable if they have a low color tint, but there are some exceptions.
It is most desirable for a gemstone to have a pure color, but most often a stone will have secondary colors. For example, a very valuable ruby can have a pure blood red color, but it can also have shades of pink to the darkest purple. A pure color can be one of the primary colors of red, blue, and yellow, while secondary colors such as purple, green, and orange result from mixing the primary colors.
'Pure' hues are rarer and therefore valued higher by the market. A good example besides ruby is pink sapphires. A 'pure' pink or violet is found much rarer worldwide than a pinkish-violet or a violetish-pink color hue. This does not apply per se to mixed colors, but pure colors without complementary hues are valued much higher, especially for pink sapphires. Comparably, blue sapphires have a pure blue hue, without a grayish-blue or greenish-blue color component.
The amount of black or white shades added to the base color determines the color tone of a sapphire. A stone should not be so dark that its color cannot be seen, nor should it be too pale. For this reason, medium intensities of medium-dark to light-medium color intensity are considered to be of higher quality in terms of color. Dark, pale, and very pale sapphires are priced more favorably. However, a sapphire is never graded solely by its color intensity. The value of a sapphire is largely determined by the combination of hue and intensity or saturation. It is not ideal for a gemstone to be too dark or too light, from an objective point of view for the finest qualities based on color evaluation, however, the saturation of a gemstone always remains a matter of taste for the viewer.
While color is the desired criterion in a colored gemstone, and stones should preferably have some traces of black or white, it is not desirable for a stone to contain too many shades of gray or brown. The fewer shades of gray or brown a sapphire contain, the higher its saturation level. Gemstones with high color saturation are called vivid or strong saturation stones.
There are some attempts by certain laboratories or gemstone appraisers as well as gemstone producers to make a quantitative color grading. However, these prove to be extremely difficult in practice as they are mostly subjective. For this reason, the color determination is similar to the clarity of a gemstone with a quantified scale with all colored gemstones and thus also with the sapphire not as trivial possible as with a diamond. This is due to the nature of the colored gemstone and its three color components: Hue, tone, and saturation.
The color of a sapphire does not reveal its origin. Sapphires come from many countries that have a wide range of colors. However, there are countries of origin where a certain color tone and saturation are more common. Often, specific colors or hues or color intensities are used to infer a country of origin. This is objectively no guarantee, only a first clue.
Yes, color distribution is an important quality criterion when assessing sapphire color. An evenly distributed color over the surface of the stone is desirable. If the sapphire shows different color zones or color interruptions in its color that do not appear homogeneous when viewed from above the stone, this is not ideal. This is unfortunately observed with many sapphires on the market, because visually less attractive, especially when viewed as a loose stone, even though this can often be compensated for in jewelry processing by the respective setting. For this reason, a sapphire with an even and homogeneous color distribution is considered to have a higher value.
Sapphires come in all three primary colors: Blue, Yellow, and Red. In addition, the color spectrum can be classified into many other hues as well as tones from light to dark. Sapphires get their color from trace elements in the mineral corundum. Classic blue sapphires contain iron and titanium, the additional element chromium gives corundum the color pink, a higher concentration of chromium makes a sapphire more reddish and so at a certain degree to a ruby.
When one thinks of sapphires, the first thing that comes to mind is an intense blue color. However, there are natural sapphires in almost every color of the rainbow including pink, rose, violet, yellow, orange, green, blue-green, or white (colorless) as well as brown, gray, and even almost black. Special color combinations like the rarest sapphire and the Padparadscha sapphire as a color combination of pinkish-orange or orangish-pink are possible, but very rare. In addition, there are "color-changing" sapphires and "two-color" sapphires that nature gives us, a true variety of colors.
In the blue sapphire, the coloring substances are iron and titanium, and in the violet sapphire, vanadium. Trivalent iron causes yellow and green hues, and chromium pink and pink colors. Orange hues are formed by chromium, iron, and vanadium in sapphire. In ruby, it is a strong concentration of chromium that gives the color, and in brownish red hues, there is an additional iron component.
The mineral sapphire with the chemical composition Al2O3 (aluminum oxide is the oxygen compound of the chemical element aluminum) is counted to the class of oxide minerals. Together with red ruby and colorless leucosaphire, sapphires form the corundum group.
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