Grading method of lab grown emerald
Emerald grading mainly divides the quality level of emerald from the aspects of color, clarity, clarity optimization and fire color. There are corresponding methods and requirements for this level division.
1、 Lightness and lightness and chroma Division
1. Division Rules
If the lightness and color of the emerald to be graded are the same as that of a standard sample, the lightness and color level of the standard sample are the lightness and color level of the emerald to be graded.
If the lightness and chromaticity of the emerald to be graded are between two adjacent continuous standard samples, the lower lightness and chromaticity level represents the lightness and chromaticity level of the emerald to be graded.
The lightness and chroma of the emerald to be graded are higher than the highest level of the standard sample, and the highest level is still used to represent the lightness and chroma level of the emerald to be graded.
The lightness and color of the emerald to be graded are lower than the lowest level of the standard sample. The lowest level is used to represent the lightness and color level of the emerald to be graded.
2. Observation method
Under the specified observation environment, make the gem about 25cm away from the light source, hold the waist of the gem, observe the same part or color card of the gem and the standard sample from the table direction, shake the gem about 30 ° angle, and classify the color of the gem according to the reflected color.
2、 Larity grading
Under specified conditions, observe the type, size, number and location of internal and external characteristics of gemstones, and divide the cleanliness level according to its impact on the beauty of gemstones.
3、Larity grading optimization level
Under the condition of microscope magnification, use the reflected light to observe the size, number and location of the gap on the emerald surface, and observe the amount of filler in the emerald gap in combination with the lighting of optical fiber lamp, so as to comprehensively divide the purity optimization level of emerald.
4、 Briliance grading
Under the specified observation environment, make the gem about 25cm away from the light source, observe the gem crown from the table direction, shake the gem at an angle of about 30 °, and divide the fire color level according to the proportion of luster in the crown area.
Emerald grading shall be carried out indoors without direct sunlight, and the color tone of grading environment shall be white or neutral gray. During grading, the specified graded light source shall be used for lighting, and the neutral white (light gray) paper (board) without fluorescence and obvious directional reflection shall be used as the observation background.
The color temperature of the lighting source used for Emerald grading is 4500k ~ 5500k, and the color rendering index is not less than 90.