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 Post subject: Raman/PL Results: Jade types and polymers detection
PostPosted: Tue Apr 30, 2013 8:39 am 
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Jade - Identifying jade type and possible polymer impregnation

Raman spectroscopy is a fast method for separating jadeite from other jade types, including omphacite and nephrite. In many cases it is possible to identify resin impregnation in order to differentiate A-type from B-type jadeite.

Jade identification

Raman spectroscopy offers a fast method for distinguishing jade from it's numerous imitations. Jadeite (Fei Cui) and nephrite have unambiguously different Raman fingerprints so they are automatically identified and separated by GemmoRaman software's library search function. Additionally, extented range acquisition is able to spot for water peaks in nephrite at about 3680 cm-1.

Figure 1: Raman spectra of Jadeite and nephrite Jade

Image

TIP: Some jadeites may exhibit very strong fluorescence masking Raman features when initially exposed to green laser. This fluorescence may be reduced by using the built-in Photo-Bleaching feature of GemmoRaman software. Usually a less than one minute photo-bleaching procedure reduces general fluorescence enough for allowing better resolution of Raman peaks. Unfortunately, some jadeite samples does not react to Photo-Bleaching. In this case it is suggested to try other spots on the sample.



Jadeite vs. omphacite

Jadeite and omphacite creates a solid series. Approximate end member percentage of both end members can be estimated by careful measurement of the "690 cm-1" Raman peak. The center of this peak is at 680cm-1 for 100% omphacite, and for pure jadeite it is shifted to about 700 cm-1. If peak position lies between these values the sample consists of both end members. For example, 50/50 omphacite-jadeite shows the peak at approximately 690 cm-1.


Figure 2: Raman spectra of Jadeite and Omphacite Jade

Image



B-type resin impregnated jadeite

Jadeite is commonly treated by bleaching, dyeing and impregnation. The most commonly used chemicals for impregnation are resins or other polymers which can be identified by series of peaks near 3000 cm-1 and 1610 cm-1. Basically, untreated A-type jadeite does not have any Raman peaks above the 1100 cm-1 line. It should be noted that VIS-NIR spectroscopy is needed for testing the origin of color. Typically coloring agents of C-type (dyed) jade can not be seen in Raman or PL spectrum.


Figure 3: Raman spectra of A-type vs. B-type Jadeite

Image



REFERENCES

Danilo Bersani, Pier Paolo Lottici
: Applications of Raman spectroscopy to gemology, Analytical and Bioanalytical Chemistry (2010)

FURTHER READING

Shane F. McClure
: GIA News from research - The Jadeite/Omphacite Nomenclature Question

Michael S. Krzemnicki: Jade

Dominic Mok: Fei Cui (Jadeite Jade) Testing

enjoy!!

Alberto & Mikko

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 Post subject: Re: Raman/PL Results: Jade types and polymers detection
PostPosted: Sun May 12, 2013 7:25 am 
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Nice read, thanks.
Though one needs spectroscopy for testing the origin of color, it seems that since the Raman spectra can detect the filler then that would be enough for many separations as very few would be filled without first dying and very few would be dyed without completing the enhancements by filling, right? I am just thinking out loud about equipment cost as both set ups will require some savings. Best regards, Lee

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