A method for in-situ micro-damage detection of oil painting pigments based on surface-enhanced Raman spectroscopy

Abstract

The application discloses an oil painting pigment in-situ micro-damage detection method based on surface enhanced Raman spectrum. The oil painting can be detected in-situ by using the surface enhanced Raman spectrum detection technology combined with an enhancing reagent. The enhancing system has a very low dosage and has a small influence on the artwork. The deposition depth of the nanoparticles can be controlled. The fluorescence interference is significantly reduced. The method is suitable for various structural types of pigments.

Description

Technical Field

[0001] This invention relates to the field of spectroscopic detection technology, specifically to a method for in-situ detection of micro-damage in oil paints based on surface-enhanced Raman spectroscopy. Background Technology

[0002] Raman spectroscopy is a spectroscopic analysis method based on molecular vibrational information. It has advantages such as being non-destructive, requiring small sample quantities, and having strong molecular fingerprint recognition capabilities. It has wide applications in fields such as pigment identification, art testing, and material analysis.

[0003] Oil paintings typically consist of an undercoat, a layer of pigments, and a varnish. The pigments are complex, including inorganic mineral pigments (such as mercuric sulfide and titanium dioxide), organic synthetic pigments (such as phthalocyanine pigments), and natural organic dyes (such as carmine).

[0004] Existing methods for detecting oil paint pigments mainly include microscopic sampling analysis, Raman spectroscopy analysis, and surface-enhanced Raman spectroscopy analysis. However, existing technologies still have the following problems: (1) Severe fluorescence interference: A large number of organic dyes and resin binders in oil paint pigments are prone to producing strong fluorescence background in conventional Raman detection, which seriously affects the identification of Raman characteristic peaks. (2) Weak signal intensity: Some organic pigments and trace components have low Raman scattering cross sections, making it difficult to obtain sufficient signal-to-noise ratio under conventional detection conditions. (3) Existing SERS methods mostly require sampling: Most surface-enhanced Raman methods require scraping pigment samples or transferring samples to metal nano-substrates for detection, which is not conducive to the protection of cultural relics. (4) Direct spraying of nanoparticles is prone to pollution: Directly spraying nanoparticles onto the surface of artworks may produce residual pollution or uncontrollable deposition, affecting the preservation of cultural relics. (5) Uncontrollable enhancement area and poor repeatability: Traditional enhancement systems often have difficulty controlling the penetration depth and enhancement area, which may affect the deep structure.

[0005] Therefore, there is a need to develop a micro-volume, controllable, and locally enhanced SERS detection method to achieve in-situ micro-damage detection of oil paint pigments. Summary of the Invention

[0006] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a method for in-situ micro-damage detection of oil paints based on surface-enhanced Raman spectroscopy (SERS) to solve the problems mentioned in the prior art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for in-situ micro-damage detection of oil paint pigments based on surface-enhanced Raman spectroscopy, the method comprising: 1-15 μL of enhancing reagent was dropped onto the surface of the oil painting to be tested, dried, and the excitation wavelength of the Raman spectrometer was set to 785 nm. In-situ detection was performed directly on the surface of the oil painting. The dropping rate of the enhancing reagent was controlled so that the nanoparticles were mainly deposited in the sample surface layer within the range of 10-30 μm. The enhancing agent is a gold / silver nanoparticle solution with an average particle size of approximately 50 nm. The preparation method of the enhancing agent includes: preparing gold / silver nanoparticles using a sodium citrate reduction method and controlling the concentration of gold / silver nanoparticles to be 0.1–1.0 mg / mL; then dispersing the gold / silver nanoparticle solution in an ethanol / water mixed solvent system, wherein the volume ratio of ethanol to water in the ethanol / water mixed solvent system is 1:20–1:50, and the volume ratio of the gold / silver nanoparticle solution to the ethanol / water mixed solvent is 1:1–1:10.

[0008] Preferably, the method is used to identify whether an oil painting contains organic pigments, inorganic pigments, or coordination pigments.

[0009] Preferably, the method is used to identify whether an oil painting contains any one or more of carmine, Prussian blue, mercuric sulfide, or titanium dioxide.

[0010] Preferably, the rate of the enhancing agent is controlled to be no more than 10 drops per minute.

[0011] Preferably, the amount of the enhancing reagent added is any one of 1-2 μL, 3-4 μL, 4-6 μL, 6-8 μL, 8-10 μL, 10-12 μL, or 12-15 μL.

[0012] Preferably, the drying conditions are natural drying at room temperature for 2-5 minutes.

[0013] Preferably, the excitation power of the Raman spectrometer is ≤2mW.

[0014] Compared with the prior art, the beneficial effects of the present invention are: The detection method of this invention requires no sampling, enabling in-situ detection; the enhancement system requires extremely low dosage, resulting in minimal impact on artworks. It allows for control over the deposition depth of nanoparticles; significantly reduces fluorescence interference; and is suitable for pigments with various structural types. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the SERS detection method for in-situ micro-damage to oil paint pigments according to the present invention.

[0016] Figure 2This is a schematic diagram illustrating the deposition of the micro-volume controllable enhancement system of the present invention in the layered structure of oil painting. When the drop volume is controlled within the range of 0.5–10 μL, the nanoparticles are mainly deposited in the surface 10–30 μm region; when the drop volume is increased to more than 10 μL, the enhancement system exhibits obvious penetration, and the signal of the underlying pigment is enhanced.

[0017] Figure 3 This is a comparison of the Raman spectra of the natural organic pigment carmine under unenhanced and enhanced conditions.

[0018] Figure 4 The images show a comparison of the enhancement effects of pigments with different structural types, where: (a) is a comparison of the Raman spectra of mercuric sulfide; and (b) is a comparison of the Raman spectra of Prussian blue.

[0019] Figure 5 The following diagrams are used to verify the surface preferential enhancement effect: (a) shows the enhancement effect of the surface pigment green when about 2 μL of enhancement reagent is added; (b) shows the change of Raman signal when the volume of the enhancement system is continuously increased.

[0020] Figure 6 The image shows a comparison of the effects of reagent addition volume on the enhancement effect and penetration depth. (a) shows the Raman spectrum changes of Pigment Yellow under different addition volumes; (b) shows the Raman spectrum at 1326 cm⁻¹. -1 Graph showing the relationship between the enhancement factor of characteristic peaks. Detailed Implementation

[0021] This invention relates to the fields of art conservation and spectral analysis technology, and in particular to an in-situ micro-damage detection method for oil paints based on surface-enhanced Raman spectroscopy (SERS), which is applicable to the in-situ identification and analysis of organic, inorganic, and coordination pigments in cultural relics and artworks.

[0022] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0023] The above embodiments are for illustrating the implementation schemes disclosed in this invention and should not be construed as limiting the invention. Furthermore, various modifications listed herein, as well as variations in the methods and compositions of the invention, will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the invention has been specifically described in conjunction with various specific preferred embodiments, it should be understood that the invention should not be limited to these specific embodiments. In fact, various modifications as described above that are obvious to those skilled in the art to obtain the invention should be included within the scope of this invention.

[0024] Example 1: Detection of trace enhancement in natural organic pigments (1) Construction of a trace-controllable enhancement system 1. Preparation of silver nanoparticles Silver nanoparticles were prepared by a sodium citrate liquid-phase reduction method. 100 mL of a 1 mmol / L silver nitrate aqueous solution was heated to boiling, and 1 mL of a 1% (w / w) trisodium citrate aqueous solution was quickly added. The mixture was kept at boiling and refluxed for 1 h. After the reaction was complete, the mixture was allowed to cool naturally to room temperature. The reaction solution was centrifuged at 5000 rpm for 5 min, and the supernatant was discarded. The precipitate was redispersed and resuspended in 100 mL of a 0.01% (w / w) trisodium citrate aqueous solution to obtain a colloidal solution of silver nanoparticles with a concentration of 0.1 mg / mL.

[0025] 2. Solvent system regulation The silver nanoparticles were dispersed in an ethanol / water mixed solvent system. The volume ratio of ethanol to water in the ethanol / water mixed solvent system was 1:20, and the volume ratio of the silver nanoparticle solution to the ethanol / water mixed solvent was 1:1.

[0026] (2) Sample preparation Uses natural organic pigment: carmine.

[0027] Pigment powder and acrylic emulsion binder were mixed at a mass ratio of 4:1 and stirred thoroughly for 10 minutes to form a homogeneous slurry. The resulting slurry was then uniformly coated onto a clean glass substrate, with the coating thickness controlled at 150±20μm, and allowed to dry naturally at room temperature (20–25℃) for 24 hours.

[0028] (3) In-situ Raman detection under unenhanced conditions Micro Raman spectroscopy was used for detection, with the following parameters: excitation wavelength: 785 nm; laser power: ≤2 mW; single-point integration time: 10 s; cumulative irradiation time in a single region: ≤30 s. Unenhanced Raman spectra were collected at the same detection point of the sample as a control. No obvious color change or surface ablation was observed under the above conditions.

[0029] (4) Micro-controllable enhancement treatment Use a micropipette to draw 2 μL of the silver nanoparticle enhancement system (generally 0.5–5 μL is sufficient), drop the enhancement system onto the center of the detection area, and allow it to air dry at room temperature for about 3 minutes.

[0030] By controlling the drop volume and solvent evaporation rate, the nanoparticles are mainly deposited in the 10–30 μm range on the sample surface.

[0031] (5) Enhanced detection Raman spectroscopy was performed on the sample again under the same detection parameters and detection location as before and under the same conditions.

[0032] Figure 3 This is a comparison of the Raman spectra of the natural organic pigment carmine under unenhanced and enhanced conditions. The results show that after adding the enhancement system of this invention, the intensity of the pigment's characteristic Raman peaks is significantly increased, and the overall signal intensity is increased by approximately 3–15 times; simultaneously, the fluorescence background is significantly reduced, and the spectral signal-to-noise ratio is significantly improved.

[0033] The above results demonstrate that the method of the present invention can effectively enhance the detection of natural organic pigments under micro-damage conditions, thereby improving the Raman detection sensitivity of weak signal pigment materials.

[0034] The results demonstrate that the micro-enhancement detection method constructed in this invention can effectively enhance the Raman signal of natural organic pigments without significantly damaging the sample structure, and is suitable for in-situ detection of micro-damage in oil painting materials.

[0035] Example 2: Adjusting the solvent ratio to detect different samples (1) Construction of a trace-controllable enhancement system Silver nanoparticles were prepared in the same manner as above, but centrifuged and resuspended for 20 mL, with a concentration of 0.5 mg / mL; the ethanol / water volume ratio was 1:35, and the colloid to solvent volume ratio was 1:5.

[0036] (2) Sample preparation Same as Example 1.

[0037] (3) Micro-controllable enhancement treatment Add 2 μL of the enhancement system and allow it to air dry for 3 min.

[0038] (4) Enhanced detection The Raman characteristic peaks are significantly enhanced, and the signal intensity is improved.

[0039] Example 3: Adjusting the solvent ratio to detect different samples (1) Construction of a trace-controllable enhancement system Silver nanoparticles were prepared in the same manner as above, but centrifuged and resuspended for 10 mL, with a concentration of 1 mg / mL; the ethanol / water volume ratio was 1:50, and the colloid to solvent volume ratio was 1:10.

[0040] (2) Sample preparation Same as Example 1.

[0041] (3) Micro-controllable enhancement treatment Add 2 μL of the enhancement system and allow it to air dry for 3 min.

[0042] (4) Enhanced detection The Raman characteristic peaks are significantly enhanced, and the signal intensity is improved.

[0043] Example 4: Verification of the enhancement of coordination pigments Prussian blue, a coordination pigment, was selected as the test object. Samples were prepared according to the method described in Example 1, and Raman spectroscopy was performed under the same conditions.

[0044] Figure 4 (b) Comparison of Raman spectra of Prussian blue samples under unenhanced and enhanced conditions. The results show that after adding the enhancement system of this invention, the intensity of the characteristic Raman peaks of Prussian blue is significantly improved, with the overall signal intensity increasing by approximately 2–8 times. Simultaneously, there are certain differences in the degree of enhancement for different vibrational peaks, indicating that the enhancement effect is related to the structural characteristics of the pigment molecules and their coordination environment.

[0045] The experimental results further demonstrate that the enhancement detection method constructed in this invention is not only applicable to natural organic pigments and inorganic pigment systems, but also has a good enhancement effect on pigment materials with coordination structure characteristics, reflecting the good applicability of this method to pigment systems with different structural types.

[0046] Example 5: Enhanced Detection of Inorganic Pigments Inorganic mercuric sulfide pigment was selected as the test subject. This pigment showed obvious Raman characteristic peaks even under unenhanced conditions.

[0047] Figure 4 (a) Comparison of Raman spectra of mercury sulfide samples under unenhanced and enhanced conditions. The results show that after adding the enhancement system of this invention, the intensity of the characteristic Raman peaks of mercury sulfide is significantly improved, the overall signal intensity is increased by about 1.5–3 times, and the signal-to-noise ratio of the spectrum is further improved.

[0048] Furthermore, no obvious peak position changes or thermal decomposition phenomena were observed during the test, indicating that the enhancement method of the present invention does not cause significant damage to the inorganic pigment structure while improving the signal intensity.

[0049] The above results show that the trace enhancement detection method constructed in this invention is not only applicable to organic pigment systems, but also has a good enhancement effect on inorganic pigments, and has good versatility.

[0050] This result further demonstrates that the micro-enhancement system constructed in this invention can effectively enhance the Raman signal while maintaining the stability of the sample structure, and is suitable for the detection and analysis of different types of pigment materials.

[0051] Example 6: Validation of Surface-Priority Enhancement in Layered Simulated Samples To verify the role of the micro-enhancing system in the layered structure of oil painting, a simulated layered sample was constructed for testing.

[0052] (1) Substrate preparation Inorganic pigment titanium dioxide was selected. It was mixed with acrylic emulsion at a mass ratio of 4:1 to prepare a base coating with a thickness of 200±50μm, and dried at room temperature for 24h.

[0053] (2) Surface preparation Organic pigment Pigment Green 7 was coated onto the bottom surface with a thickness controlled at 100±30μm, and allowed to dry naturally for 24 hours, forming a double-layer simulated oil painting structure sample.

[0054] (3) Enhanced detection Add 2 μL of the silver nanoparticle reinforcement system and allow it to air dry for 3 min. A control experiment was also conducted by adding 10 μL of the reinforcement system.

[0055] (4) Experimental results Figure 5 This image shows the effect of the method of the present invention on the preferential enhancement detection of the surface layer in the layered structure of an oil painting. The structure of the experimental sample is as follows: the surface layer is pigment green, and the bottom layer is titanium dioxide.

[0056] Figure 5 a shows the Raman detection results after adding approximately 2 μL of the enhancing reagent, compared with the Raman spectrum without the addition of the enhancing reagent. The results indicate that the characteristic Raman signal of the surface pigment green was significantly enhanced after adding a trace amount of the enhancing reagent, while the signal was weaker under the unenhanced condition. This demonstrates that the enhancement system of this invention can achieve effective surface signal enhancement under trace amounts.

[0057] Figure 5 b represents the Raman detection results obtained as the amount of enhancing reagent added increases. Wherein: The red curve is the Raman spectrum after adding 10 μL of enhancing reagent, at which point the detected signal is still mainly the characteristic Raman signal of the surface pigment green; the blue curve is the Raman spectrum after adding 12 μL of enhancing reagent, at which point the characteristic peak signal of the underlying titanium dioxide begins to appear; the black curve is the Raman spectrum after adding 15 μL of enhancing reagent, at which point the characteristic signal of the underlying titanium dioxide is further enhanced.

[0058] The experimental results above demonstrate that by controlling the volume of the reinforcing reagent added, layer-by-layer reinforcement detection of materials in different layers of an oil painting's structure can be achieved. When the amount of reinforcing reagent is small, the reinforcement effect is mainly concentrated on the surface material; as the amount of reinforcing reagent increases, the reinforcement system gradually penetrates into the underlying structure, thus enabling the detection of the bottom layer material. The method of this invention can achieve controllable reinforcement detection of the layered structure of oil painting materials, possessing excellent tomographic identification capabilities and application value.

[0059] (5) Conclusion By controlling the drop volume of the enhancement system and the ratio of the solvent system, surface-specific enhancement detection can be achieved.

[0060] Example 7: Effect of reagent addition volume on enhancement effect and penetration depth To investigate the effect of the added volume of the enhancement system on the surface enhancement effect and penetration behavior, the organic pigment Pigment Yellow was selected as the test object.

[0061] (1) Sample preparation Pigment yellow powder and acrylic emulsion binder are mixed at a mass ratio of 4:1 and stirred thoroughly for 10 minutes to form a homogeneous slurry.

[0062] The slurry was evenly applied to the surface of a clean glass substrate, and the coating thickness was controlled to be 150±20μm. It was then allowed to dry naturally at room temperature for 24 hours.

[0063] (2) Enhanced system treatment The silver nanoparticle reinforcement system prepared in Example 1 was used.

[0064] Different volumes of the enhancing reagent were added using a micropipette: 0μL, 1μL, 2μL, 4μL, 6μL, 8μL, 10μL.

[0065] Each addition was allowed to air dry at room temperature for about 3 minutes after each addition.

[0066] (3) Raman detection conditions The detection was performed using a micro Raman spectrometer: excitation wavelength: 785 nm; laser power: ≤2 mW; Raman spectra were collected in the same detection area.

[0067] (4) Experimental results like Figure 6 The figure shows the effect of the added volume of the enhancement system on the Raman signal enhancement effect. Pigment yellow was used as the test sample.

[0068] Figure 6 (a) Raman spectra obtained under different enhancing reagent drop volumes. Experiments were conducted with 0, 1, 2, 4, 6, 8, and 10 μL of enhancing reagent added. The results showed that the Raman characteristic peak intensity of pigment yellow gradually increased with the gradual increase of the enhancing system drop volume, indicating that the deposition amount of the enhancing system on the sample surface gradually increased, thereby improving the detection intensity of the Raman signal.

[0069] With 1326cm -1 Using the characteristic peaks at certain points as the analysis object, the ratio of the enhanced Raman signal intensity to the unenhanced signal intensity is calculated to obtain the corresponding enhancement factor, such as... Figure 6 As shown in (b). The results show that as the volume of the enhancing reagent added increases, 1326 cm⁻¹ -1 The enhancement factor of the characteristic peak gradually increases, showing a clear increasing trend.

[0070] The above results show that the micro-enhancement system constructed in this invention can effectively control the degree of Raman signal enhancement by adjusting the dropping volume, providing a stable and controllable enhancement method for the micro-detection of oil paint pigments.

[0071] Experimental results show that when the dropping volume is in the range of 1–4 μL, the Raman signal is significantly enhanced; when the dropping volume is further increased to 6–8 μL, the enhancement effect continues to improve; when the dropping volume reaches 10 μL, the enhanced system shows obvious penetration.

[0072] Combination Figure 5 The results show that when the added volume is large, the reinforcing system may gradually penetrate into the lower pigment structure.

[0073] (5) Conclusion This result further demonstrates that by controlling the drop volume of the enhancement system, not only can the Raman signal intensity be controlled and enhanced, but the deposition and penetration behavior of the enhancement system on the sample surface can also be adjusted, thereby achieving detection and control of materials at different layers.

[0074] The above description is merely an illustrative embodiment of the present invention and is not intended to limit the scope of the invention. Any equivalent changes and modifications made by those skilled in the art without departing from the concept and principles of the present invention should fall within the scope of protection of the present invention. Furthermore, it should be noted that the components of the present invention are not limited to the overall application described above. Each technical feature described in the specification can be used individually or in combination as needed. Therefore, the present invention naturally covers other combinations and specific applications related to the inventive points of this case.

Claims

1. A method for in-situ detection of micro-damage in oil paints based on surface-enhanced Raman spectroscopy, the method comprising: 1-15 μL of enhancing reagent was dropped onto the surface of the oil painting to be tested, dried, and the excitation wavelength of the Raman spectrometer was set to 785 nm. In-situ detection was performed directly on the surface of the oil painting. The dropping rate of the enhancing reagent was controlled so that the nanoparticles were mainly deposited in the sample surface layer within the range of 10-30 μm. The enhancing agent is a gold / silver nanoparticle solution with an average particle size of approximately 50 nm. The preparation method of the enhancing agent includes: preparing gold / silver nanoparticles using a sodium citrate reduction method and controlling the concentration of gold / silver nanoparticles to be 0.1–1.0 mg / mL; then dispersing the gold / silver nanoparticle solution in an ethanol / water mixed solvent system, wherein the volume ratio of ethanol to water in the ethanol / water mixed solvent system is 1:20–1:50, and the volume ratio of the gold / silver nanoparticle solution to the ethanol / water mixed solvent is 1:1–1:

10.

2. The method according to claim 1, characterized in that: The method described above is used to identify whether an oil painting contains organic pigments, inorganic pigments, or coordination pigments.

3. The method according to claim 1, characterized in that: The method described above is used to identify whether an oil painting contains any one or more of carmine, Prussian blue, mercuric sulfide, or titanium dioxide.

4. The method according to claim 1, characterized in that: The rate of the enhanced reagent is controlled to be no more than 10 drops per minute.

5. The method according to claim 1, characterized in that: The amount of the enhancing reagent added is any one of the following ranges: 1-2 μL, 3-4 μL, 4-6 μL, 6-8 μL, 8-10 μL, 10-12 μL, or 12-15 μL.

6. The method according to claim 1, characterized in that: The drying conditions are natural drying at room temperature, with a drying time of 2-5 minutes.

7. The method according to claim 1, characterized in that: The excitation power of the Raman spectrometer is ≤2mW.

Images