A method for identifying Hetian jade using Raman spectroscopy

Abstract

This application discloses a Raman spectroscopy method for identifying Hetian jade, belonging to the field of jade identification technology. This application involves directly performing Raman spectroscopy on the sample at wavelengths of 100–3200 cm⁻¹. ‑1 Raman spectra within the specified intervals are obtained and compared with standard spectra. Regions with prominent fluorescence, low and broad characteristic peaks are selected for scanning. The surface of the selected jade area is observed, and area surface or line scans are performed using a 785nm excitation source at cracks or color boundaries to obtain the final Raman spectrum. The characteristic peaks of benzene series compounds or C-H stretching vibrations of alkanes appearing in different intervals are used to identify Hetian jade. This method does not damage the jade itself, preserves its value, and is simple to operate with high sensitivity.

Description

Technical Field

[0001] This invention relates to the field of jade identification technology, and in particular to a method for identifying Hetian jade using Raman spectroscopy. Background Technology

[0002] Hetian jade, renowned both domestically and internationally, is also known as Chinese jade. As one of China's four famous jades, it is highly prized for its fine texture, warm luster, and rich colors, making it a valuable collectible. Xinjiang Hetian jade, due to its unique skin color and texture, can fetch tens of thousands of yuan per gram. However, the market has seen the emergence of products using chemical agents to imitate the natural texture and skin color of Hetian jade, passing it off as genuine Hetian jade. Some of these chemical agents are highly toxic to the human body, and long-term wear is detrimental to health. Currently, the identification of natural and dyed Hetian jade remains an industry challenge, and the new national standard GB / T38821-2020 "Hetian Jade" does not specify methods for identifying the skin color of Hetian jade.

[0003] Dyed Hetian jade primarily uses nephrite jade from Xinjiang, Qinghai, or Russia. The process involves four steps: rolling, sandblasting, coloring, and waxing. These techniques mimic the natural color formation process of Hetian jade, resulting in a smooth surface and high colorfastness. In the jade industry, jade quality assessment mainly relies on traditional performance tests such as hardness, density, refractive index, and thermal conductivity, as well as visual inspection with a magnifying glass. Ultraviolet-visible absorption spectroscopy and infrared spectroscopy are also used to identify jade varieties. Proton-excited X-ray fluorescence (PIXE) and X-ray diffraction (XRD) are commonly used to analyze the petrological characteristics of Hetian jade samples, obtaining information on trace elements contained within the jade.

[0004] Early gemstone identification techniques relied on the difference in color transition between natural and dyed Hetian jade pebbles, using the human eye to visually identify dyed Hetian jade. While methods like proton-excited X-ray fluorescence and X-ray diffraction have high sample preparation requirements, this paper offers a non-destructive, highly sensitive method for identifying dyed Hetian jade to protect its intrinsic value. Summary of the Invention

[0005] To address the technical problems of complex identification processes and potential damage to Hetian jade in existing technologies, this invention proposes a highly sensitive and gentle Raman spectroscopy method for identifying Hetian jade.

[0006] To achieve the above objectives, the technical solution provided by this invention is as follows:

[0007] (1) Wipe the sample to be tested with an alcohol swab and let it dry. Fix the sample onto a glass slide using modeling clay. Select a flat area of ​​the Hetian jade surface and make a 100-3200 cm² sample. -1Raman spectroscopy was performed within the interval to obtain Raman spectrum A, which was then compared with the standard spectrum to observe the fluorescence envelope and the peak intensity and broadening of characteristic peaks.

[0008] (2) Select areas with obvious fluorescence, low and broad characteristic peaks for scanning, observe the surface of the jade in the selected area, find cracks or the boundary between light and dark colors under low magnification, switch to X50 magnification at the cracks or the boundary between light and dark colors, and use a 785nm excitation light source to perform area surface scanning or line scanning to obtain the Raman spectrum B of the sample to be tested.

[0009] In some embodiments, the sample to be tested is Hetian jade, dyed Hetian jade, or artificially polished Hetian jade.

[0010] In some embodiments, the Raman spectrum B at 1550–1630 cm⁻¹ -1 The sample to be tested that contains characteristic peaks of benzene series compounds within the range is dyed Tianyu jade.

[0011] In some embodiments, the Raman spectrum B at 1200–1400 cm⁻¹ -1 The test samples containing non-fixed alkane CH stretching vibrations within the range are dyed or artificially polished Hetian jade.

[0012] In some embodiments, the Raman spectrum further includes a fluorescence effect.

[0013] Its main advantages are:

[0014] (1) Non-destructive. No special preparation is required for the sample, and it can be tested quickly and non-destructively in its original state, which is an ideal method for testing finished gemstone jewelry.

[0015] (2) Non-contact. Rapid and non-destructive testing of inclusions inside gemstones, capable of identifying both fluid and solid inclusions.

[0016] (3) High sensitivity. Raman spectroscopy is more sensitive to nonpolar bonds such as carbon-carbon double bonds and aromatic rings, so it is extremely effective for detecting organic substances injected or filled into gemstones. Attached Figure Description

[0017] Figure 1 This is a Raman spectrum characteristic peak calibration diagram of Hetian jade according to an embodiment of the present invention.

[0018] Figure 2 These are the spectroscopic characteristics of dyes and resins according to an embodiment of the present invention. Wherein a is 100-2000 cm⁻¹. -1 Interval spectroscopic characteristics, b is 700-1800 cm⁻¹ -1 Interval spectral characteristics.

[0019] Figure 3 The spectroscopic characteristics of graphite inclusions and residual finishing agents according to an embodiment of the present invention are shown. Where 'a' represents 100-2000 cm⁻¹. -1 Interval spectroscopic features, b is 1000-2000 cm⁻¹ -1 Interval spectral characteristics.

[0020] Figure 4 These are characteristic peaks from different embodiments. Where 'a' is 800–200 cm⁻¹. -1 Raman spectra of artificially treated samples within the range, b represents the comparison of characteristic peak intensities of benzene derivatives.

[0021] Figure 5 These are comparison images of fluorescence effects and PCA plots for different embodiments. Figure a shows a comparison of fluorescence effects in Raman spectra, and figure b shows the PCA plots of the artificially treated sample and the natural sample. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Certain terms involved in this application have the following meanings:

[0024] The term "and / or" refers to any and all combinations of one or more of the related listed items.

[0025] The following detailed description is provided with reference to specific embodiments. Unless otherwise specified, the following embodiments do not include components other than unavoidable impurities.

[0026] Unless otherwise specified, the reagents and instruments used in the examples are conventional choices in the art.

[0027] Experimental methods not specified in the examples were performed under conventional conditions, such as those described in literature or books, or methods recommended by the manufacturer.

[0028] Raman spectroscopy was performed using a Renishaw-Invio microconfocal Raman spectrometer (Renishaw, UK). The excitation source was a near-infrared semiconductor laser with a wavelength of 785 nm, and the excitation light power illuminating the sample surface was approximately 50 mW. Raman signals were acquired under a 50x Leica objective lens, with a CCD integration time of 3 seconds. WIRE 4.2 software was used for peak shape fitting of the test spectra.

[0029] The samples can be divided into three categories: Category 1 is dyed Hetian jade, with fine cracks on the surface, which has been treated with dye or filling; Category 2 is chemically polished Hetian jade, with a smooth surface, which has been polished or treated at high temperature; Category 3 is natural Hetian jade pebble material, with a smooth and translucent surface, which has not undergone any chemical treatment.

[0030] Example 1

[0031] (1) Wipe the natural Hetian jade with an alcohol swab and let it dry. Use modeling clay to fix the sample on a glass slide. Select a flat area of ​​the Hetian jade surface and make a sample 100-3200 cm². -1 Raman spectroscopy was performed within the interval to obtain Raman spectrum A, which was then compared with the standard spectrum provided by the instrument to observe the fluorescence envelope and the peak intensity and broadening of characteristic peaks.

[0032] (2) Select a region with obvious fluorescence and low and broad characteristic peaks for scanning. Mark the selected region as T. Observe the surface of the jade in the selected region. Look for cracks or the boundary between light and dark colors under a low magnification lens. Switch to X50 magnification lens at the cracks or the boundary between light and dark colors. Use a 785nm excitation light source to perform a surface scan or line scan of the region to obtain the Raman spectrum B of the sample to be tested.

[0033] Figure 1 This is the Raman spectrum of natural Hetian jade. The strongest peak of the Raman characteristic spectrum appears at 679 cm⁻¹. -1 This peak value is related to the "symmetric stretching-bending vibration" of Si-O-Si in the tetrahedral ring composed of silicon-oxygen tetrahedra, and is a characteristic peak value of amphibole minerals. It is located between 100 and 1100 cm⁻¹. -1 There are three main peak ranges within the interval, including 800–1100 cm⁻¹. -1 Classified as Si-O stretching vibration, 600–800 cm⁻¹ -1 Belongs to the symmetric stretching-bending vibrations of Si-O-Si, 100–600 cm⁻¹ -1 Bending vibrations and lattice vibrations belonging to metal oxides

[0034] Example 2: Identification of Dyed Hetian Jade

[0035] (1) Wipe the natural Hetian jade with an alcohol swab and let it dry. Use modeling clay to fix the sample on a glass slide. Select a flat area of ​​the Hetian jade surface and make a sample 100-3200 cm². -1 Raman spectroscopy was performed within the interval to obtain Raman spectrum A, which was then compared with the standard spectrum provided by the instrument to observe the fluorescence envelope and the peak intensity and broadening of characteristic peaks.

[0036] (2) Select a region with obvious fluorescence and low and broad characteristic peaks for scanning. Mark the selected region as F1. Observe the surface of the jade in the selected region. Look for cracks or the boundary between light and dark colors under a low magnification lens. Switch to X50 magnification lens at the cracks or the boundary between light and dark colors. Use a 785nm excitation light source to perform regional surface scanning or line scanning to obtain the Raman spectrum B of the sample to be tested.

[0037] (3) Observe the 1550-1630 cm⁻¹ region in Raman spectrum B. -1 Are there any accompanying characteristic peaks of benzene series compounds within the interval?

[0038] A line scan was performed on the crack in the Hetian jade marked F1, and the results were obtained. Figure 2 a, 100~1200cm -1 The range showcases some characteristic peaks of Hetian jade, ranging from 700 to 1700 cm. -1 Several spectral peaks that do not belong to tremolite appeared within the range. Figure 2 zoom in locally Figure 2 b. Mark the position of each peak. The peaks in Table 1 are assigned according to the literature, with the peak appearing at 1442 cm⁻¹. -1 The spectral peak at 1735 cm⁻¹ is a characteristic peak of azobenzene dyes. -1 The peaks at 1615 and 1579 cm⁻¹ are characteristic peaks of saturated acetate surfactants, which are commonly used to clean jade. -1 These are characteristic peaks of benzene derivatives.

[0039] Table 1. Analysis of characteristic peaks of dyes and resins

[0040] <![CDATA[Peak position / cm -1 > compound Vibration type 837 Isopropyl Frame extension 898 Tetrahydropyrrolidone Ring expansion 1051-1071 Fatty sulfoxides S=O telescopic 1131 Ketones C = C = O (expansion / contraction) 1313 Ethylene <![CDATA[In-plane deformation of CH2]]> 1442 Azobenzene N = N stretching 1579-1615 benzene series compounds Ring expansion (bi-peak) 1735 Cyclopropane Ring expansion

[0041] Example 3: Identification of Artificially Polished Hetian Jade

[0042] (1) Wipe the artificially polished Hetian jade with an alcohol swab and let it dry. Fix the sample onto a glass slide using modeling clay. Select a flat area of ​​the Hetian jade surface and make a sample 100–3200 cm². -1 Raman spectroscopy was performed within the interval to obtain Raman spectrum A, which was then compared with the standard spectrum provided by the instrument to observe the fluorescence envelope and the peak intensity and broadening of characteristic peaks.

[0043] (2) Select a region with obvious fluorescence and low and broad characteristic peaks for scanning. Mark the selected region as F2. Observe the surface of the jade in the selected region. Look for cracks or the boundary between light and dark colors under a low magnification lens. Switch to X50 magnification lens at the cracks or the boundary between light and dark colors. Use a 785nm excitation light source to perform regional surface scanning or line scanning to obtain the Raman spectrum B of the sample to be tested.

[0044] (3) Observe the 1550-1630 cm⁻¹ region in Raman spectrum B. -1 Are there any accompanying characteristic peaks of benzene series compounds within the interval?

[0045] A depth scan was performed on the boundary between light and dark colors of the Hetian jade marked F2, and the results were obtained. Figure 3 a, 100~800cm -1 The area showcases some characteristic peaks of Hetian jade, ranging from 1000 to 2000 cm. -1 Several characteristic peaks not belonging to tremolite components appeared within the range. Figure 3 The blue area is zoomed in. Figure 3 b. Mark the position of each peak. The peaks in Table 2 are assigned according to the literature. 1587cm -1 The spectral peaks at this location are related to the natural graphite crystal inclusions within the Hetian jade. The peaks are relatively short and broad, indicating that the jade underwent high-temperature steaming, acid and alkali corrosion during processing, which damaged its crystallinity.

[0046] Table 2. Analysis of characteristic spectral peaks of graphite inclusions and finishing agents.

[0047] <![CDATA[Position / cm -1 > compound Vibration type 1017 Monosubstituted benzene CH In-plane Deformation 1111 hydrazine NN stretching on the benzene ring 1177 Monosubstituted benzene CH Deformation 1307 n-Alkanes <![CDATA[In-plane torsion of CH2]]> 1371～1432 Secondary nitroalkanes <![CDATA[Symmetric NO2 stretch]]> 1505 Naphthalene Skeletal vibration 1587 Graphite crystals - 1830 Ethylene carbonate -

[0048] Example 4: Characteristic peaks of artificially treated Hetian jade

[0049] Fifteen artificially treated Hetian jade samples were selected based on the depth of their surface color and labeled as 1 to 15. Samples ranging from 800 to 2000 cm in size were made. -1 Raman spectra within the specified range. Observation: 1200–1400 cm⁻¹ -1 Does the interval contain non-fixed alkane CH stretching vibrations, or 1550–1630 cm⁻¹? -1 Are there any accompanying characteristic peaks of benzene series compounds within the interval?

[0050] Test results are as follows Figure 4 As shown in a, all samples were at 1075, 1615, and 1579 cm⁻¹. -1 Characteristic peaks appear at [location missing], with the 1075 peak representing the Si-O stretching vibration of tremolite. The 1615 and 1579 peaks always appear together, representing the ring stretching vibrations of benzene derivatives. Arrange the test spectra in sequence, such as... Figure 4As shown in b, as the color lightens, the characteristic peaks at 1579 and 1615 also weaken, proving that these two peaks are caused by the dye. (At 1200-1400 cm⁻¹) -1 Within the range, many characteristic peaks appear. These peaks do not have fixed positions and are caused by the stretching vibration of alkane CH.

[0051] Example 5: Fluorescence effect of artificially treated Hetian jade

[0052] Principal component analysis (PCA) was performed on the Raman spectra of 10 dyed and chemically polished Hetian jade samples and 10 natural Hetian jade samples. The spectral ordinate was used as the "important sensory" input, and the output results are as follows: Figure 5 As shown in b.

[0053] Figure 5 a represents Hetian jade samples that have undergone artificial dyeing (F1), chemical polishing (F2), and no artificial treatment, ranging from 100 to 3200 cm². -1 The Raman fluorescence spectrum within the range shows characteristic peaks concentrated in the 100–1100 cm⁻¹ range. -1 Within the interval. Figure 5 As can be seen from a, the fluorescence effects of samples F1 and F12 are significantly higher than those of sample T. Figure 5 b clearly shows the PCA of dyed Hetian jade, chemically polished Hetian jade, and natural Hetian jade, with no overlap, and can clearly distinguish between natural Hetian jade and artificially treated Hetian jade.

[0054] In summary, from the Raman spectra of the observed samples, the 1200–1400 cm⁻¹... -1 Does the interval contain non-fixed alkane CH stretching vibrations, or 1550–1630 cm⁻¹? -1 The presence of characteristic peaks of benzene series compounds within the specified range allows for accurate determination of whether a sample has been artificially dyed or polished. This method for identifying Hetian jade can accurately distinguish between natural Hetian jade, dyed Hetian jade, and artificially polished Hetian jade.

Claims

1. A method for identifying Hetian jade using Raman spectroscopy, characterized in that, Includes the following steps: (1) Wipe the sample to be tested with an alcohol swab and let it dry. Fix the sample onto a glass slide using modeling clay. Select a flat area of ​​the Hetian jade surface and make a 100-3200 cm² sample. -1 Raman spectroscopy was performed in the interval to obtain Raman spectrum A, which was then compared with the standard spectrum to observe the fluorescence envelope and the peak intensity and broadening of characteristic peaks. (2) Select areas with obvious fluorescence and low and broad characteristic peaks for scanning. Observe the surface of the jade in the selected area. Find cracks or the boundary between light and dark colors under low magnification. Switch to X50 magnification at the cracks or the boundary between light and dark colors and use a 785nm excitation light source to perform area surface scanning or line scanning to obtain the Raman spectrum B of the sample to be tested.

2. The method for Raman spectroscopy identification of Hetian jade as described in claim 1, characterized in that, The sample to be tested is Hetian jade, dyed Hetian jade, or artificially polished Hetian jade.

3. The method for Raman spectroscopy identification of Hetian jade as described in claim 1, characterized in that, The Raman spectrum B shows a range of 1550–1630 cm⁻¹. -1 The sample to be tested that contains characteristic peaks of benzene series compounds within the range is dyed Tianyu jade.

4. The method for Raman spectroscopy identification of Hetian jade as described in claim 1, characterized in that, The Raman spectrum B shows a range of 1200–1400 cm⁻¹. -1 The test samples containing non-fixed alkane CH stretching vibrations within the range are dyed or artificially polished Hetian jade.

5. The method for Raman spectroscopy identification of Hetian jade as described in claim 1, characterized in that, The Raman spectrum also includes fluorescence effects.

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