Lab grown sapphire grading method

The grading of sapphire mainly divides the quality level from the aspects of color, clarity, fire color and quality, classifies its heat treatment and describes the cutting.

1、 Color grading

The color of sapphire is classified by colorimetry under the specified environment.

Observation method:

under the specified observation environment, make the gem about 25cm away from the light source, hold the gem waist, observe the gem from the table direction, shake the gem about 30 ° angle, and classify the color of the gem according to the reflection color and fire color.

2、 Value level

Before dividing the value level of graded sapphire, its tone category and chromaticity level should be determined first.

Using the standard sample corresponding to the chromaticity level of the sapphire to be graded, the color gray value is obtained by comparing the neutral gray card. The color value level of sapphire to be graded is determined according to the obtained gray value range.

3、 Larity grading

Observation method:

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.

4、 Briliance grading

Observation method:

under the specified observation environment, make the gem about 25cm away from the light source, hold the gem waist, 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 brilliance in the crown area and brightness.

5、 Representation of heat treatment

Observation method: under the specified conditions, observe whether the inclusions (acicular rutile fracture, zircon halo, etc.) in the gem have changed to distinguish whether they have undergone heat treatment; Then, on the premise of determining the heat treatment of gemstones, the heat treatment categories are further divided according to the amount of residues in cracks and / or pits.

6、Grading requirements

Environmental requirements:

Sapphire 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.

Gradinglight：The color temperature of the lighting source used for Sapphire grading is 4500k ~ 5500k, and the color rendering index is not less than 90.