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Color Grading System
Color Change CZ
Colored Glass Filters
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        The Gemological Laboratory has been engaging in gemological research, colored diamond identification, colored diamond grading, and gemstone identification services. We issue gemstone identification report with necessary spectral curve, such as VU-VIS-IR spectrum, UV fluorescence spectrum, photoluminescence spectrum, FTIR spectrum for jadeite identification. We include a digital image of the reported gemstone in the report. The digital image can be used as a digital "fingerprint" and saved for future rechecking.


Colored Diamond Identification

We use the Liulabs MDIS-i6 multifunction dual integrating sphere spectrometer to measure the spectra of visible reflectance, UV fluorescence and photoluminescence, and a FTIR spectrophotometer to measure the IR spectrum for identifying colored diamonds. Depending on the color and the spectral peaks of the colored centers in the visible spectrum, UV fluorescence spectrum and photoluminescence spectrum, such as the N3, H3, H4, 550 nm, NV, S-V and GR1 centers, the origins of most colored diamonds can be identified as natural, synthetic, treated or other mixed types. The IR spectra are also used to identify the types and other characteristics properties of colored diamonds for identification purposes.


Color Gemstone Identification

We identify colored gemstones by spectroscopy methods using the Liulabs multifunction spectrometer and FTIR spectrophotometer. We measure the visible, UV fluorescence, photoluminescence and IR spectra of gemstones, and compare the spectra with the spectra in our database to identify each gemstone. Our spectroscopy method for gemstone identification is much more advanced than the traditional gemological method using spectrocope, refractometer, microscopy etc.  


Color Grading of Colored Diamonds and Gemstones   

We use the Liulabs multifunction spectrometer and the computer color grading system to grade the colors of colored diamonds and gemstones by the Universal Color System. We also provide color grades of the modified color grading system of GIA for colored diamonds (see Figure 1). In addition, our color grading report includes the CIELAB a*, b*, hue, saturation and lightness, which can be used for pricing colored diamonds precisely. The visible spectrum, UV fluorescence spectrum, photoluminescence spectrum, and IR spectrum  measured by the Liulabs spectrometer and FTIR spectrophotometer can be provided upon request.

Figure 1. Spectral measurement and color grading of a treated synthetic fancy vivid greenish blue diamond by the Liulabs multifunction spectrometer.


Jadeite Identification and Color Grading   

We provide jadeite identification service using the Liulabs multifunction spectrometer, FTIR spectrophotometer, and an advanced digital imaging system. Our Identification Report including five sections: Sample Description, Picture, IR Spectrum, Color Grade, and Conclusion. The weight, size, color, cut of a tested sample will be described in the Sample Description section. We have developed an advanced digital imaging system for gem identification. This system can also provide a high resolution digital image, which is usually used for picture in the Report. We will store this digital image as "fingerprint" of the sample for future identification purpose. We assign the types of A B, C, or B+C based on the IR spectrum and visible spectrum. The color grade is directly provided by the Liulabs spectrometer with the Jadeite Color Grading plug-in software. In the Conclusion section, we give a precise conclusion without any confusion. 

Figure 2. Jadeite color grading of the Liulabs multifunction spectrometer.


Grading of the Alexandrite Effect   

The alexandrite effect refers to the color change of gemstones under different light sources. It is a non-color-constancy phenomenon. The gemstones with the alexandrite effect are usually more valuable and sought after by collectors. The alexandrite effect has been classified into four categories depending on the hue change under different pairs of light sources.

The plug-in software of Alexandrite Effect Grading can grade the alexandrite effect of gemstones under CIE standard illuminants A, D65, F7, and F11 (see Figure 3).  There are 6 alexandrite effects between different CIE standard illuminants, and 5 grades based on the hue angle differences in the CIELAB color space. The 5 grades of the alexandrite effect are None, Weak, Intense, Strong, and Vivid. The hue angle change ranges of the 5 alexandrite effect grades are:



Hue Angle Difference


< 20


>= 20 and < 40


>= 40 and < 60


>= 60 and < 80


>= 80


Figure 3. Alexandrite effect Grading by the Liulabs multifunction spectrometer.


Melee Screen  

We provide melee screen service to identify natural melee from synthetic melee by UV fluorescence using the Liulabs multifunction spectrometer. Most natural colorless to light yellow melees have the N3 center at 415 nm. Our melee screen fee is very competitive at as low as $1 for each melee.




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Last modified: 01/22/15.