HomeJadeite Jade and FTIR

Abstract
FT-IR provides a rapid and definitive tool for discrimination of "A" and "B" jade.

Introduction
The key to the value of gemstones lies in their beauty. The obvious problem is that beauty can be enhanced by non-natural methods. When disclosed, this is not illegal; however, fraud is a a concern.



There are three classes for jadeite jade commonly available. A-Jadeite is natural jadeite, B-jadeite is treated as discussed below, and C-jadeite material is artificially colour-enhanced. C-jadeite is fairly easy to spot, but B-jadeite materials are not.

B-jade starts as raw jadeite with stains. The jade is soaked in acide to remove the stains. This weakens the stone by leaching out structural materials. The pores generated are filled with wax or epoxy resin, whose index of refraction closely matches jade. Besides potential fraud, this treatment may cause skin burns from residual acid, and discolouration of the epoxy resin can occur.

After polymer impregnation of the leached jadeite, the resultant refractive index of B-jadeite is correct for jadeite. UV spectroscopy is not sufficiently diagnostic. Microscopy may not show enough detail to identify the treatment. So B-jade may pass as A-jade.

Fourier Transform infrared(FT-IR) easily discriminates A-jade and B-jade. The analysis takes only a few seconds, and the procedure is unambiguous.

This technique uses the infrared region of the electromagnetic spectrum. The term infrared is derived from being lower in energy than the red end of the electron magnetic spectrum. The unit of measurement for infrared energy is the wavenumber (number of waves per centimeter), which is expressed in reciprocal centimeters (cm-1). In the infrared, however, spectral features generally arise from the vibration of molecules and the structural components of the crystal. Every group of atoms has a number of intrinsic vibration frequencies that correspond to rocking, stretching, or bending of the bonds between atoms of the group. The absorption band generated gives a typical spectrum, which can be interpreted by a trained gemologist. Professor Fritsch et al (1992) formerly at GIA but now at University of Nantes, France, introduced this important method of testing of jadeite.

Experimental
A Nicolet 380 FT-IR spectrometer from Thermo Electron can be used in the analysis. Samples of A and B jadeite jade are mounted using "blu-tac", although care must be taken to prevent contamination of the jade. A 4X beam condenser was used here, but this is not essential.

The data was collected using Thermo's OMNIC software, and 64 scans at 4cm-1 resolution. Signals below 2300cm-1 were obscured, but the critical range between 2600 and 3800 cm-1 is clear.

Results
Spectra from A and B-jade are shown. The B-Jade has a large peak located in the aliphatic hydrocarbon region. The differences are immediately obvious. Amazingly, the limited open spectral region is sufficiently diagnostic to identify the class of material used. Searching against Thermo's FT-IR libraries, the top hits are all epoxy resins.

The FT-IR analysis of gemstones is simple and non-destructive. OMNIC allows SOPs to be constructed, to allow operators unfamiliar with FT-IR to use the method. The speed of analysis could allow incorporation into bulk testing facilities, and the inexpensive nature of the 380 whould allow even small retailers to use it. The analysis could be extended using TQ Analyst, Thermo's chemometrics program, to include quality checks and identification of known treatments.

Natural jadeite (untreated)

 

Most of the jadeite samples tested were opaque from 400 to 2300cm-1. They all showed a broad, asymmetric absorption band centered approximately between 3400 and 3550 cm-1. This band may be fairly smooth in shape, or it may show a number of narrow accessory peaks, e.g. 3580 or 3725cm-1. The untreated samples were found to have two sharp bands at 2920 and 2850cm-1 which belongs to residues of wax used after polishing. Virtually all material is waxed before it enters the market. The spectrum indicates below shows the presence of wax peak at 2920 and 2850 cm-1.

 
 
 

No visible spectrum related to bleaching.

Bleached and polymer-impregnated jadeite:

 

With the present of wax at 2920 and 2850 cm-1, additional peaks are found along 2965, 2930, 2875cm-1 (mid-infrared region). There is also a companion feature at about 3035 cm-1. In the near-infrared, weak but sharp additional bands are seen at approximately 4060, 4620, 4680 and 5986 cm-1. The spectrum below indicates presence of polymer peaks.

 

2875 cm-1

 



Conclusions
Reference 1 states that "B Jade is here to stay." This is not inherently illegal, unless the treatment is not documented. Most precious stones are susceptible to enhancement. FT-IR is an effectivel tool in uncovering treated stones, which should assist in enforcing disclosure.

References

1. Hughes, R.W; Galibert, O.; Bosshart,G.; Ward,F.; Oo,T.; Smith,M.; Sun, T.T.; Harlow,G. Burmese Jade: The Inscrutable Gem Part 2: Jade Trading, Grading & Identification

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