What is Colored Sapphire [Sapphire Introduction Course 3]

Colorful sapphires

Although the term "sapphire" is only applicable to blue corundum varieties, it has become a common practice in the jewelry industry to use sapphire as a suffix for almost all other color corundum varieties: yellow sapphire, pink sapphire, purple sapphire or just colored sapphire. As shown in the above picture, the color range of corundum gemstones covers almost the entire color system.

Among them, rubies and pink sapphires are colored by trace chromium (Cr3); while yellow sapphires are colored by magnesium and color centers called color centers; lotus sapphires (orange-pink to pink-orange corundum varieties) are a mixture of chromium and magnesium plus color centers. Obviously, there can be a variety of color combinations, which makes sapphires very rich in color.

In Myanmar, Madagascar, Sri Lanka, Tanzania and Australia, some famous ruby and sapphire mines have produced or are still producing fascinating colored sapphires.

The most sought-after varieties of these colors are pink sapphire, lotus sapphire and yellow sapphire. Among them, the main reason why yellow is popular comes from India. In this country, varieties of this color have extraordinary significance and demand for them is also increasing.

Due to the subtle color changes of colored sapphires, they are mostly used for glamorous and gorgeous colored jewelry. Due to their high hardness, good gloss, and usually excellent transparency, colored sapphires may be more popular in the future.

Lotus Sapphire

Lotus sapphire has a pinkish-orange to orange-red hue of medium to low saturation. The earliest known alluvial ore was produced in Sri Lanka. Today, Tanzania and Madagascar also produce this elegant and charming corundum variety. The latest deposit discovered near Ambatondrazaka in Madagascar at the end of 2016 also produces Lotus sapphire, and this deposit is also an important blue sapphire production area.

According to the guidelines of the Laboratory Coordinating Committee LMHC (SSEF is one of the founding members of the committee), there are the following rules and restrictions for the naming of Lotus Sapphire:

The name of the lotus sapphire is not limited by its origin. When viewed in standard daylight, its color must be a subtle and soft pink-orange to orange-pink mixed hue with medium and low saturation.

The name% 20 "Lotus Sapphire% 20" should not be used in the following cases.

• If the gemstone contains any hue other than pink or orange;

• When observing the gemstone with the naked eye, the color of the gemstone is in the range of plus or minus 30 degrees of angle on the table, and the distribution is obviously uneven;

• The existence of yellow or orange secondary matter in the cracks of the gemstone affects the overall color of the gemstone;

• The gemstones are diffused, filled with high refractive index glass, irradiated, etc.

• Gems are dyed, coated, painted or sprayed, etc.

• If the color of the gemstone is unstable and exceeds the color range of the lotus sapphire during the color stability test (such as the color changes to pink)

Lotus Sapphire is an intermediate between pink sapphire and orange sapphire with low to moderate color saturation. Many of the gems in this picture cannot be called Lotus Sapphire, which is enough to show the difficulty of defining her color. Photo: SSEF

A standard Lotus Sapphire colorimetric map (created by F. Notari in 1996), based on the Munsell Color System (which describes colors based on three attributes: hue, chroma, and color value), this colorimetric map is used as one of the color references. Photo: Michael Krzemnicki, SSEF

Color Stability: Yellow and Other Colored Sapphires

The color of corundum is usually related to the presence of trace chromogenic elements, such as chromium (red of ruby) and iron-titanium combination (blue of sapphire). Therefore, for these gemstones, the more trace chromogenic elements, the more saturated and deeper the color of the gemstone. The color of the color sapphire is more complicated, because there is more than one reason for the color of their color, and it also includes the so-called color center color. The color center is actually a structural defect at the atomic level inside the gemstone. When it is activated, it will absorb light of certain wavelengths (for yellow sapphires, it is mainly the blue hue in the visible light spectrum), resulting in different shades of yellow.

An untreated yellow sapphire of more than 50 carats with unstable color and reversible change: before the fading test (left), after the fading test (middle), after ultraviolet irradiation (right). Photo: SSEF

However, yellow sapphires are not the only ones that may have color stability problems.

Some colored fancy sapphires with lotus-like sapphires may also have similar situations that affect their naming. These gems will show obvious color changes over time, changing from obvious pink-orange to pink within a few weeks. Similar to the yellow sapphires described above, these colored gems with unstable colors can also regain their color to a certain extent after a short period of ultraviolet radiation and become pink-orange (slowly returning to their original pink under sunlight). In other words, the stable color of these gemstones is actually pink (related to chromium), while the superimposed unstable color is yellow (due to the existence of unstable yellow color centers), so that the gemstone appears: If the yellow color center is stimulated, the overall color of the gemstone will change to orange pink to pink orange.

The reason why this colored sapphire has this unusual color change (instability) is very similar to the yellow sapphire mentioned above. Its subtle color similar to the lotus sapphire is actually a mixture of weak absorption associated with chromium (resulting in pink) and extensive absorption in the yellow center.

An untreated colored sapphire from Madagascar. After color stability tests, it shows a color change from pink orange (similar to lotus sapphire color) to pink. Photo: SSEF, SSEF, SSEF.

A colored sapphire from Ambatondrazaka, Ambatondrazaka (Madagascar) shows a pink color (actually the stable color of this gem related to chromium). After the yellow color center is stimulated, the gem shows a pink orange color, and then returns to a pure pink (back to a stable color) after the fading process. Photo: SSEF