## 4 The Example of the Green Stones
### The Chromophores Study and the UV-Vis/NIR Spectroscopy Application  
A UV-Vis/NIR analysis is suitable for Green Stones to distinguish between natural color or treated color (Figure 10). Indeed, bleaching and dyeing treatments for modern jade materials are relatively common [84]. In particular, the dyeing procedure, usually subsequent to the \"bleaching\" and impregnation treatment, is a treatment able to increase the jade colors (in this case, the green is discussed, but the treatment is not limited to it), due to the addition of artificial pigments [158,159]. In geology, the terms jade-C, when it is only dyed, and jade-B + C, when it is impregnated and dyed, are commonly accepted [84]. As per the polymer impregnation treatment discussed above, the detection of artificial or enhanced colorations for green jadeite can be evaluated for authenticity. In Figure 10, two reference absorption spectra of natural green jadeite and dyed green jadeite are reported, (a) and (b), respectively. In parallel, the spectra acquired by a gemological handheld spectroscope on the same materials have been reported below the corresponding UV-Vis Spectra (Figure 10c,d). The visible range can be considered diagnostic due to the presence of the Cr3+ characteristic absorptions at about 633, 657, and 692 nm corresponding to the jadeite-jade A, naturally green, or the broad absorptions between 600 and 700 nm for dyed green jadeite (jade B + C). Figure 10: (**a,b,e,f**) UV-Vis/NIR and (**c,d**) gemological handheld spectroscope spectra of Green Stones. Spectra acquired by UV-Vis/NIR spectrophotometer Lambda 950, PerkinElmer, equipped with integration sphere, Spectrum Software. The two “handheld” spectra (**c,d**) have been reported flipped to highlight the similarities in the band absorption in correspondence to the top spectra. In particular, (**a**) Natural Imperial Green Jadeite-Jade A, the sharp absorption at about 633, 657, and 692 nm, correlated with Cr3+, should be noted; (**b**) Treated Jadeite-Jade B + C, note the broadening of the bands corresponding to orange and red visible ranges (photos and spectra: [PERSON], gemological handheld spectroscope images: [PERSON], GECI); (**c**) Dyed Green chalcedony (Jade imitation), it is interesting to observe the absorptions in the same areas of the natural Cr3+ but showing characteristic broader bands, especially about 710 nm. These impregnations and modern dyeing treatments are performed using chromium-rich pigments; (**f**) Natural chrysoprase color is due to nickel-associated minerals, as shown by the characteristic UV-Vis/NIR spectrum, with the absorption centered at about 645 nm. (Data and photos: [PERSON], GIG). Because of Green Stones massive and frequently natural porous textures, dyeing treatments are very common in the trade, not only for the jades but also applied to other gemstone materials, such as the chalcedony. By applying UV-Vis/NIR spectroscopy, as reported in Figure 10e, the identification of the Cr-rich artificial pigment results is less evident than the jadeite dyeing example. Still, it can be diagnosed because of the broader absorptions of the band at about 710 nm. Consequently, the visible range is not enough and must be expanded through the NIR. In spite of this being easily possible by UV-Vis/NIR digital spectrophotometers (whether benchtop or optical fibers portable system), the gemological handheld spectroscopic does not allow the analysis beyond the visible range (400-700 nm). Moreover, the digital spectrophotometers are obviously more sensitive than the handheld gemological spectroscope. In the case of dyeing suspects, a deep OM study is mandatory: frequently, the dyed samples show characteristic colors concentrations along the fractures [84; 158; 160]. Similarly, the analysis of chrysoprase with natural color shows a diagnostic UV-Vis/NIR spectrum (Figure 10f), where the broad absorption correlated with nickel chromophore is visible in the range between 600 and 800 nm [106], as an asymmetric band centered at about 645 nm.