Color, origin and degree of optimization are the main factors affecting the value of sapphire. Based on a large number of research data of the guild for many years, the Standard for Appraisal and Classification of Sapphire gives an authoritative and objective classification interpretation of blue sapphire from three aspects: color, origin and optimal treatment.
The gas-liquid inclusions in sapphire are distributed along the healing cracks.
First, color grading? Color grading sapphire is corundum with blue as the main tone, often with purple or green tone. According to the three elements of color (hue, saturation and lightness), GUILD classifies the color of sapphire into the following grades:
-Light
-medium.
-Nervous.
-Vivid
-Deep
Schematic diagram of sapphire color classification
(1) "Royal Blue" Royal Blue
"Sapphire" is a kind of true blue or purple blue, which is one of the highest ratings of sapphire color by the guild and belongs to bright blue and deep blue.
Bright blue or dark blue with certain saturation and lightness can reach the level of "sapphire blue". In the guild sapphire color grading system, "sapphire" is not limited to its place of origin.
"cornflower blue" cornflower blue
"cornflower blue" is a kind of blue with purplish hue, which gives people a unique texture like hazy velvet. Named after the blue of German national flower cornflower, it belongs to bright blue and intentional blue.
When the gem contains finely dispersed granular, short needle-like inclusions or growth lines, the scattering of light through the gem will lead to this visual effect. Cornflower sapphire was first produced in Kashmir, India. "Centauri Blue", like "Royal Blue", is not limited to the place of origin, and every place of origin may produce sapphire with "Centauri Blue".
"cornflower blue"&; Amp "royal blue" sapphire
In GUID gemstone laboratory, each sapphire needs 2-3 gemologists with formal training. Under standard laboratory conditions, based on standard sapphire colorimetric stones accumulated by GUID for many years, scientific, stable and reliable color grades can be obtained according to formal operation procedures.
Second, optimize the treatment? Strengthening and heat treatment are commonly used to optimize the treatment of sapphire, which can change the color or purity of sapphire to varying degrees. Because whether sapphire is heat-treated will affect the price of sapphire, GUILD will disclose the information of whether sapphire is heat-treated in each gem report.
According to microscope observation and large-scale instrument test, the heat treatment grade of sapphire can be divided into the following grades:
-No signs of thermal enhancement
There is no sign of heat treatment.
-H: indication of thermal enhancement
Clear signs of heat treatment
-H( 1): thermal enhancement indicator of trace residues.
Clear signs of heat treatment and trace residues.
-H(2): There are obvious signs of thermal enhancement of residues.
Clear signs of heat treatment and significant residues.
Gas-liquid inclusions expand after heating, and internal ions diffuse blue after heating, mostly in the form of internal diffusion.
Third, geographical origin In the market, there are differences in the value of sapphires from different origins. For decades, GUILD has accumulated a large number of sapphire sample data from all over the world, including Myanmar, Sri Lanka, Kashmir, Madagascar, Tanzania and other major sapphire producing areas.
The origin of sapphire can be inferred by analyzing the inclusion characteristics, spectrum, chemical composition and other parameters of gem. Because of the complexity and similarity of different geological origins, the parameters of gems from different origins overlap, so not every sapphire can judge the definite origin.
Niobium in Madagascar Sapphire and Three Groups of Directional Rutile Needle Inclusions in Myanmar Sapphire, an Iron-rich Mineral.
Four. Summary As shown in the figure below, the Guild Sapphire Certificate explains the color classification, origin and optimization in detail.
Detailed explanation of the parameters of English certificate of guild sapphire
At present, GUILD's classification standard for sapphire identification is mainly applicable to blue sapphire. Blue is divided into five levels: light, medium, thick, fresh and dark.
Royal blue is represented by bright blue * or deep blue *; Cornflower blue is represented by bright blue * or strong blue *, and there are comments in the comments section.
Heat treatment is a common optimization method for sapphire, which can change the color or purity of sapphire to varying degrees. The guild's heat treatment grades for sapphire are N, H, H( 1) and H(2). (Click to learn more about sapphire optimization and identification)
Sapphire from different places of origin has different values. GUILD can identify major sapphire producing areas such as Myanmar, Sri Lanka, Kashmir, Madagascar and Tanzania. It is worth noting that not every sapphire can determine the exact origin.