DOI: https://doi.org/10.21203/rs.3.rs-2117156/v1
As one of the common physical materials in Chinese archaeological excavations, ancient bronzes are important bases for studying the development of Chinese bronze culture, which is of great significance for exploring the development law of ancient human culture and reconstructing ancient human society. However, the ancient bronzes unearthed by archaeological excavations have been corroded to varying degrees under the dual influence of the soil burial environment and the sudden change of the above-ground environment, which has led to the different health status of the cultural relics. An adequate scientific evaluation of these bronzes is needed to inform how they should be extracted, moved and transported, as well as how subsequently they should be restored.
Based on the analysis and research of relevant industry standards and the disease characteristics of bronzes to determine the risk factors affecting the health status of unearthed cultural relics, and then determines the main content of the health assessment of bronzes. By studying methods to effectively characterize the health status of bronzes and combining laboratory research to form a systematic method for in situ nondestructive analysis of bronzes. Through the systematic analysis of the detection results of the evaluation indicators to establish an analysis model for the health evaluation of bronzes. Finally, this paper achieves a scientific and effective evaluation of the health status of bronzes unearthed from archaeological sites. This enabled the feasibility of the extraction methods to be evaluated using the excavated Sanxingdui bronzes as samples.
Ancient Bronzes are important physical materials for the study of ancient societies. In recent years, with the continuous advancement of infrastructure construction in China, an increasing number of bronzes have been unearthed. Under the dual influence of the soil burial environment and the sudden change of the above-ground environment, the health status of cultural relics is subjected to change. Directly taking emergency extraction, packaging and transportation methods may cause "secondary damage" of cultural relics in the absence of scientific assessment and in-depth understanding of the health status of unearthed cultural relics. Therefore, it is important to construct health evaluation methods for bronzes unearthed from archaeological sites to minimize their deterioration. The scientific and effective health evaluation method should comprehensively reflect the real state and risk expectations of the unearthed bronzes, make them better to adapt to the complex and changeable environment caused by the archaeological excavation, and provide an important basis for the selection of the extraction, packaging and transportation methods of cultural relics. In addition, it can provide basic support for the emergency protection and long-term protection of ancient bronzes, so as to effectively protect and study the precious material materials for the development of ancient human society. At present, no scientific and complete health evaluation methods for unearthed bronzes have been determined at home and abroad.
In 2014, the State Administration of Cultural Heritage officially issued the Technical specification for evaluating disease of movable collection, providing new ideas and technical means for the health evaluation research of different types of mobile cultural relics. In recent years, the continuous development of scientific demands, changing industrial standards, and new scientific and technological advances have provided new insights and means for research on the health evaluation methods used for ancient bronzes. In recent years, with the continuous advancement of scientific methods and detection technology, such as CT scanning, metal ultrasonic detector, X-ray photoelectron spectroscopy (XPS), electron spectroscopy (EDAX), secondary ion mass spectrometry (SIMS), scanning electron microscopy, X-ray diffraction and other come improved instruments [1–3] that can be widely used for the qualitative or quantitative analysis of cultural relics. Data processing methods such as Grey Relation Analysis (GRA) and Analytic Hierarchy Process (AHP) are gradually introduced into the cultural relic protection research industry, which provides a suitable evaluation method for further exploring the significance of data. All these provide a solid theoretical basis for us to study and propose the health evaluation indexes, analysis methods and evaluation methods of bronzes unearthed from archaeological sites.
The current article examines the importance of establishing ancient artifacts health evaluation methods by investigating the excavation status of bronzes from a large number of archaeological excavation sites. The disease characteristics of unearthed bronzes are summarized, and the health evaluation index framework of bronzes unearthed in archaeological sites is established combined with the risk assessment theory and relevant standards. Based on this, efficient, convenient and mobile analytical methods that can adapt to the complex and changeable environment of the archaeological excavation site also could be selected. Furthermore, with the statistical analysis methods, the influence degree of the evaluation indexes, the correlation between the test results and the evaluation indexes and the authenticity of the evaluation model are analyzed, in order to complete the construction of the health evaluation method of bronzes unearthed from the archaeological site. The evaluation system discussed in this paper has been applied in typical archaeological sites in China, and has achieved good results.
The significance of the health evaluation for the unearthed cultural relics
In the archaeological sites, in order to standardize the protection of unearthed cultural relics, the State Administration of Cultural Heritage has issued a series of industry standards and norms, including the Measures of the People's Republic of China for the Administration of Archaeological Excavations Activities(Revised in 2019), the Field Archaeology Work Regulations(Released in 1984), and the Specification of shipping Packaging of Cultural Relics(GB/T 23862-2009).Relevant technical specifications from excavation, extraction, packaging and shipping have been established, and a set of relatively perfect working methods have been formed. In the extraction of cultural relics, the archaeological workers will predict the health state of the unearthed artifacts through experience, and serve as the basis for the selection of extraction, packaging and shipping methods. Therefore, the evaluation results of the health status of cultural relics unearthed in the archaeological excavation sites have become the premise and basis for guiding the extraction, packaging and shipping of cultural relics, and it will directly affect the protection and restoration of cultural relics in the later laboratory. At present, this important link usually relies on archaeological workers to predict the health status of cultural relics. The environment of the archaeological excavation site is complex and changeable, with many types of unearthed objects and very different preservation states. Due to the limitations of workers experience, it is impossible to comprehensively and accurately understand the health state of the unearthed cultural relics. However, the improper extraction and packaging and shipping methods selected here may cause "secondary damage" of the cultural relics. Therefore, it is urgent to form a comprehensive evaluation method for the health evaluation of bronzes unearthed at archaeological sites.
Research status of health evaluation indexes for bronzes unearthed
In the health evaluation method of bronzes unearthed at the archaeological site, the evaluation index is an important part. While little research into the health evaluation index of bronzes is available there is considerable research on the diseases of ancient bronzes. In 2007, the State Administration of Cultural Heritage of China issued "The bronze collections diseases and the graphic symbols for diseases"(WW/T 0004-2007). The ancient bronzes diseases were listed that included incomplete, crack, deformity, laminar deposit, perforation, strumae projecture, surface incrustation, integer crisp, pitting corrosion, crevice corrosion and general corrosion. In "Technical specification for evaluating disease of movable collection- Metal"(WW/T 0058-2014) divides the 12 common diseases into stable diseases, active diseases and induced diseases according to the nature of disease activity. The specification also mentions various disease identification and detection methods and measurement items. Unfortunately, the results are only used as a record and macro comparison, and no further comprehensive evaluation is made to form a complete health evaluation system for cultural relics.
In the past one hundred years, scholars have conducted much research on the corrosion products of bronzes. Results show that bronzes had corrosion products of different colors, such as oxides, sulfides and sulfates. The color of the corrosion products is similar to the color of minerals, such as cuprous oxide which is red cuprite, basic copper carbonate which is dark green malachite and basic cupric chloride which is green atacamite [4-5]，alkaline copper chloride is green chloride copper ore and light green parachlorine copper ore, hydroxyl chloride copper ore, etc.
Research has also been carried out on the mechanisms involved in forming these corrosion products by Scholars at home and abroad. At the beginning of the 20th century, the British scientist Vernon studied the connection between the composition of bronze corrosion products and the environment. Research by Bosi & Garagnani[6], Robbila et al.[7] and others has experimentally shown that bronze corrosion will lead to different metallographic structures. Some researchers also believe the alloy composition of the copper matrix significantly affects the surface morphology of corrosion products (e.g., Constantinides [8]). At the end of the 20th century, domestic research on the corrosion mechanism of bronzes showed that the formation of corrosion products of bronzes is not only related to the composition of the matrix itself, but also under the influence of external environmental factors. Some studies suggest that the corrosion of bronzes is largely the result of chloride, moisture and oxygen in the external environment (Jinxin[9]) resulting in the appearance of native chloride-bearing bronze corrosions (bronze disease). Chongzheng et al. [10] artificially corroded copper samples by simulating natural conditions. The analysis of the experimental results showed that chloride ions, moisture and oxygen were the basic elements of “bronze disease” and that chloride ions were the key elements. In addition, Chongzheng et al. [11] used hydrochloric acid to corrode the surface of copper samples and used instruments to analyze the occurrence and development of rust. The results showed that rust grew rapidly under acidic conditions.
Similarly，F. Soares Afonso et al. [12] investigated the effects of chloride content, oxygen, and humidity in soil on copper corrosion and demonstrated that the average corrosion rate determined from gravimetric data were in good correlation with the soil aggressiveness. There is a correlation between the corrosion mechanism of bronzes unearthed from the archaeological sites and the soil characteristics [13]. In 2005, A. G. Nord et al. [14] indicated that acidic soils, large deposits of sulfur pollutants associated with critical loads, the presence of soot and soluble salts, and conditions into water and air all could accelerate the deterioration of bronzes. Jianhong[13] et al. analyzed a total of fifteen samples from the archaeological site and from collections and believed that the unearthed bronzes did not have “bronze disease”, but formed lesions in the soil, and gradually transformed into “bronze disease” under suitable environmental conditions.
In recent years, research [16-20] has shown that many factors such as water content, pH, oxygen content, acid-base substances, soluble salts, organic matter and soil microorganisms are directly related to the formation of corrosion products. Under the influence of high humidity, oxygen-containing, chlorine-containing and acidic environments, “bronze disease” can continue to penetrate, spread and corrode the substrate, causing bronzes to perforate, loosen, and fester. If the preservation environment is not controlled in time, it will even corrode until the bronze disappears, and the infectivity it has will infect other objects around it thereby increasing the degree of destruction.
The current assessment of the health of ancient bronzes and analysis of their diseases and environmental conditions facilitates the formation of a framework index for bronze health assessment.
Research status of cultural relic health evaluation analysis model
Very little research is available on the analysis methods used for assessing the health status of bronzes although many excellent examples of well conducted evaluations exist both inside and outside the industry. Health evaluation is widely used in the construction industry – here often being termed risk, or stability, evaluation (along with similar terminology). In 2022, Ing Edsel B [21] proposed and verified that the use of AHP processes can promote equity, diversity and inclusion . Scholars have also used the analytic hierarchy process and grey relational analysis method to evaluate Serbia Saar Mountains [22], landslides [23], hybrid steel frame [24], electricity substittion projects [25], and social benefits of eco-tourism scenic areas [26], and obtain effective evaluation results. In recent years, these methods have also been applied to the field of cultural relic protection. In 2016, Xue [27] et al. used the grey correlation method to quantify the degree of disease of twenty-nine buildings on the Great Wall from Niujialiang to Qinhe in Yuyang District, northern Shaanxi, and provided a scientific basis for the protection and reinforcement measures of these single buildings. Yuanyuan[28] et al. used the entropy weight method to successfully screen the main influencing factors of bronzes corrosion when studying the influence of environmental factors on the corrosion of bronzes. They used the grey correlation method to study the correlation coefficient between the main influencing factors and bronzes corrosion.
In terms of methodological principles, Analytic Hierarchy Process (AHP) and Grey Relation Analysis (GRA) are suitable for multi-factor health evaluation. The former obtains a subjective evaluation based on expert experience (using Satty's 1-9 scale method [29] to evaluate the scores of each factor at the same two levels and obtain a judgment matrix). The latter is an objective evaluation based on a quantitative analysis of the dynamic development process of the system to examine whether the relationship between the various factors of the system is close [30]. It is an important method for studying the correlation between the internal factors of the system. The combination of the two can combine subjective and objective evaluations and reduce the risks caused by human subjective assumptions. The health evaluation of bronzes unearthed is a multi-factor evaluation. Drawing on the evaluation methods inside and outside the industry, this paper can use Analytic Hierarchy Process and Grey Relation Analysis to systematically analyze the evaluation indexes and calculate the weight of the evaluation indexes.
By reviewing research on bronzes, the contents of health evaluations can be clarified. The health assessment methods of bronzes unearthed at the archaeological site mainly include health assessment indexes, in-situ nondestructive analysis methods and evaluation model. To construct a framework of health evaluation indexes for bronzes, the primary goal is establishing the main factors that affect the health status of bronzes. These include physical, chemical and biological factors which can be used to determine those factors that most affect the preservation of bronzes unearthed. Establishing the relationship between the health degree of cultural relics and the factors influencing them, helps give a scientific characterization of the health evaluation techniques used for cultural relics. Based on the requirements of the archaeological site environment and the ontology of cultural relics, a fast, in-situ and non-destructive analysis method is studied to provide technical support for the evaluation of the health of cultural relics. Through the systematic analysis of the detection results of the evaluation indexes, the framework of the health evaluation and analysis method of bronzes unearthed is constructed. Finally, this research has formed a scientific method for evaluating the health of Bronzes unearthed at the archaeological site.
The selection and determination of evaluation indexes is the primary task and important component of constructing a health evaluation method for bronzes unearthed from archaeological sites. According to previous research and on-site investigation, the type and degree of diseases of unearthed cultural relics can directly reflect the health status of cultural relics, and the environment in which cultural relics occur will further affect the rate of disease development and deterioration. Therefore, the first-level indexes of the health evaluation of bronzes unearthed should include the health evaluation indexes of cultural relics and the reference indexes of the occurrence environment. It is worth noting that the health status evaluation index of cultural relics is the key to assessing the health status of bronzes, while the reference index of the occurrence environment reflects the risk expectations of the cultural relics and is not the key to assessing the health status of cultural relics.
Based on the health evaluation indexes of cultural relics, referring to the common disease characteristics and damage mechanism of bronzes unearthed, and the direct correlation of later extraction, packaging, transportation and emergency protection treatment, the second-level indexes of the health evaluation of bronzes unearthed at archaeological sites are as follows: completeness, corrosion degree and mechanical properties. The evaluation of the occurrence environmental reference index directly compares the buried environmental quality of bronzes in the archaeological site.
In order to further scientifically quantify the evaluation indexes, it is necessary to identify and measure the evaluation indexes, and express them in terms of quantity, area, length and other results. The quantitative results of some evaluation indexes need to be converted into percentages for the same magnitude comparison, which is caused by the different sizes of bronzes. In the process of quantifying the evaluation index, the increase of the incomplete area ratio and the length of cracks ratio of bronzes will directly reduce their stability. Considering the completeness alone, the ratio of incomplete area and the ratio of crack length can be used as the main influencing factors to characterize the completeness of bronzes. Considering the degree of corrosion of bronzes alone, the corrosion area ratio and resistance can be used as the main influencing factors to characterize the degree of corrosion of bronzes. According to the on-site judgment, the degree of corrosion that causes the substrate of bronzes to become loose, brittle and corroded above 0.1mm will seriously affect the stability of the substrate and the health of the bronzes. Therefore, the corrosion area should be measured according to the above corrosion degree. In addition, hardness is also included in the health evaluation index of cultural relics, as the main influencing factor of mechanical properties, to characterize the mechanical properties of bronzes.
According to industry standards and much scientific research results, for the reference index of the occurrence environment, humidity, temperature, electrical conductivity and salinity can be selected as the main influencing factors to reflect the health status of bronzes.
The health assessment index framework is shown in Fig. 2.
Obtaining qualitative and quantitative results reflecting the ontology materials of cultural relics by analytical means is a key way to effectively assess the health status of cultural relics. At present, there is no systematic investigation and analysis methods for bronzes during the unearthed process. According to the content requirements of the health assessment of bronzes, this paper will study the in-situ non-destructive analysis methods to effectively characterize the health status of cultural relics, and combine the research of related laboratory methods to form a systematic in-situ non-destructive analysis methods of bronzes.
In the process of quantifying the main influencing factors of bronzes, the industrial-grade DL9810 fiberglass tape measure has the advantages of high precision and easy operation, and is suitable for the measurement of incomplete area, crack length and corrosion area. Since there is currently no fast, in-situ, non-destructive method for measuring the corrosion thickness of bronzes, this study tested eddy current pulse imaging, ultrasonic testing, infrared thermal imaging and resistance analysis methods. The results showed that the eddy current pulse imaging results can reflect a certain corrosion distribution and characterize a certain corrosion depth, but the instrument is large in size and cannot meet the needs of the archaeological site. Ultrasonic testing and infrared thermal imaging are convenient to operate, but there are problems such as characterizing the degree of corrosion and reflecting the distribution of corrosion. However, the resistance test results show that the thinner the corrosion of bronzes, the lower the resistance; the thicker the corrosion, the greater the resistance, that is, the rust thickness is positively correlated with the resistance. And in a certain range, the resistance range value and the corrosion thickness range value correspond to each other, which is feasible from the experimental results. The resistance meter is easy to operate, non-destructive testing, and quick to obtain results, meeting the requirements of the complex environment of the archaeological site and the body of cultural relics. Through the experimental analysis of various instruments, the resistance meter was finally used to characterize the corrosion thickness of bronzes.
In terms of mechanical properties characterization of bronzes, the LXD-A hardness tester has low strength and is suitable for hardness measurement of low and medium hardness materials, and can effectively measure the hardness of bronzes.
The reference index of the occurrence environment will be quantified by the TR-6D soil detector, which has the function of detecting soil humidity, temperature, salinity and electrical conductivity. It can indicate the soil burial environment state of cultural relics and provide guidance for the preservation environment parameters of cultural relics.
Explore the construction of a bronze cultural relic health assessment model including an assessment index framework and analytical methods. According to the characteristics of cultural relics, the index framework is based on the quantification of indexes and the health level standard; the analysis method supports the acquisition of the main information of health assessment through a set of analysis methods and processes. The method of combining Analytic Hierarchy Process and Grey Relation Analysis is used to calculate the subjective weight and objective weight of the evaluation index, and then combine the combined weight of each health evaluation index to obtain the health value of the bronzes. Since there is no standard for the health level of bronzes at present, this paper uses 25 as the tolerance to classify the health value according to the arithmetic sequence, and divides the health level into grades I, II, III, and IV. On this basis, according to the experience judgment of the archaeological site and the health value of the cultural relics, the rationality of the classification of the health grades of bronzes was verified, and finally an effective assessment of the health of bronzes was achieved through the health grades. Through the evaluation of the occurrence environment reference index, it can indicate the state of the soil burial environment of cultural relics and provide guidance for the environmental parameters of later cultural relic preservation.
Twelve bronzes were selected from those unearthed at the sacrificial pits K7 and K8 in the sacrificial area of Sanxingdui site, including the K7-1 bronzes human figure, K7-2 bronzes, K7-3 bronzes bird, K7-4 bronzes human face, K7-5 bronzes fragment, K8-1 bronzes mythical beast, K8-2 bronzes scorpion, K8-3 bronzes mythical beast, K8-4 bronzes human figure, K8-5 bronzes zun, K8-6 bronzes zun, K8-7 bronzes human figure. Quantitative results of evaluation indexes were obtained using in situ non-destructive techniques. The quantification results of each evaluation index are shown in Table 1; the quantification results of the occurrence environment reference index are shown in Table 2.
| Cultural relic number | Incomplete area ratio | Crack length ratio | Corrosion area ratio | Resistance (GΩ) | Hardness (HA) |
|---|---|---|---|---|---|
| K7-1 bronzes human figure | 2.0% | 100% | 100% | 480.83 | 84.88 |
| K7-2 bronzes | 0.1% | 0.1% | 20.0% | 70.00 | 96.75 |
| K7-3 bronzes bird | 0.1% | 0.1% | 80.0% | 495.80 | 84.33 |
| K7-4 bronzes human face | 0.1% | 6.6% | 10.0% | 102.35 | 85.17 |
| K7-5 bronzes fragment | 90.0% | 100% | 100% | 289.04 | 44.00 |
| K8-1 bronzes mythical beast | 0.1% | 0.1% | 10.0% | 38.24 | 95.80 |
| K8-2 bronzes scorpion | 12.7% | 40.0% | 80.0% | 183.79 | 83.17 |
| K8-3 bronzes mythical beast | 0.1% | 0.1% | 32.0% | 473.97 | 94.90 |
| K8-4 bronzes human figure | 0.1% | 0.1% | 15.0% | 44.60 | 94.50 |
| K8-5 bronzes zun | 1.1% | 22.8% | 10.0% | 146.42 | 86.00 |
| K8-6 bronzes zun | 49.9% | 10.0% | 100% | 211.08 | 93.00 |
| K8-7 bronzes human figure | 16.1% | 0.1% | 100% | 297.19 | 93.00 |
| Measuring position | Humidity (%) | Temperature (℃) | Salinity (mg/L) | Conductivity (us/cm) |
|---|---|---|---|---|
| K7 | 20.5 | 19.5 | 117 | 213 |
| K8 | 24.5 | 18.3 | 165 | 301 |
According to Analytic Hierarchy Process, the subjective weight of the bronzes health evaluation index is calculated to determine its impact on the bronze’s health status. A judgment matrix was created in Table 3. The subjective weight of each evaluation index is calculated according to the judgment matrix and shown in Table 5.
| Health Evaluation Indexes | Incomplete area ratio | Crack length ratio | Corrosion area ratio | Resistance | Hardness |
|---|---|---|---|---|---|
| Defective area ratio | 1 | 1/3 | 5 | 3 | 1/5 |
| Crack length ratio | 3 | 1 | 5 | 3 | 1 |
| Rust area ratio | 1/5 | 1/5 | 1 | 1/3 | 1/3 |
| Resistance | 1/3 | 1/3 | 3 | 1 | 1/3 |
| Hardness | 2 | 1 | 3 | 3 | 1 |
The correlation coefficients of each evaluation index were calculated according to the Grey Relation Analysis and are displayed in Table 4. The objective weight was obtained by weighting the gray correlation coefficient of each index, that is, calculate the ratio of the average value of the correlation coefficient of each evaluation index to the sum of the average value of the correlation coefficient of all evaluation indexes, as shown in Table 5.
The combined weight formula: Wi=a Wi′་b Wi″. In the formula: Wi′ and Wi″ are the subjective weight and the objective weight; a and b respectively represent the relative importance of the subjective weight and the objective weight, a + b = 1, a = 0.5, b = 0.5. The combined weights were calculated and are shown in Table 5.
| Cultural relic number | Incomplete area ratio | Crack length ratio | Corrosion area ratio | Resistance | Hardness |
|---|---|---|---|---|---|
| K7-1 bronzes human figure | 0.3381 | 1.0000 | 1.0000 | 0.9386 | 0.6896 |
| K7-2 bronzes | 0.4286 | 0.4286 | 0.4737 | 0.4557 | 0.6000 |
| K7-3 bronzes bird | 1.0000 | 1.0000 | 0.3913 | 0.3333 | 0.3954 |
| K7-4 bronzes human face | 0.4323 | 0.4540 | 0.4286 | 0.4871 | 0.8146 |
| K7-5 bronzes fragment | 0.6000 | 0.6000 | 0.6000 | 0.8084 | 0.4286 |
| K8-1 bronzes mythical beast | 0.6000 | 0.6000 | 0.6000 | 0.6000 | 0.4353 |
| K8-2 bronzes scorpion | 0.3678 | 0.4543 | 0.6923 | 0.4230 | 0.6601 |
| K8-3 bronzes mythical beast | 1.0000 | 1.0000 | 0.6716 | 0.3443 | 0.3413 |
| K8-4 bronzes human figure | 1.0000 | 1.0000 | 0.9000 | 0.9730 | 0.3431 |
| K8-5 bronzes zun | 0.3359 | 0.3928 | 0.3333 | 0.3957 | 0.7104 |
| K8-6 bronzes zun | 0.5288 | 0.3569 | 1.0000 | 0.4455 | 0.8755 |
| K8-7 bronzes human figure | 0.7629 | 0.6000 | 0.4286 | 0.6825 | 0.4564 |
| Average value | 0.6162 | 0.6572 | 0.6266 | 0.5739 | 0.5625 |
| Weight | Incomplete area ratio | Crack length ratio | Corrosion area ratio | Resistance | Hardness |
|---|---|---|---|---|---|
| Subjective weight | 0.20 | 0.35 | 0.06 | 0.11 | 0.29 |
| Objective weight | 0.20 | 0.22 | 0.21 | 0.19 | 0.19 |
| Combined weights | 0.20 | 0.28 | 0.13 | 0.15 | 0.24 |
The quantitative data of evaluation indexes are uniformly processed into values positively correlated with the degree of health, that is, the data of incomplete area ratio, crack length ratio, corrosion area ratio, and electrical resistance are taken as reciprocal values, and then the new data and hardness data are normalized, and displayed in Table 6.
Health value calculation formula: \(JKZ=（a{x}_{1}+b{x}_{2}+c{x}_{3}+d{x}_{4}+e{x}_{5}）\times 100\). In the formula: \(a\)、\(b\)、\(c\)、\(d\)、\(e\) are the combined weights of each evaluation index of each bronze cultural relic; \({x}_{1}\)、\({x}_{2}\)、\({x}_{3}\)、\({x}_{4}\)、\({x}_{5}\) are the normalized data corresponding to each evaluation index of each bronze cultural relic. The health value ranges from [0-100], and the larger the health value, the healthier the bronze relic. The health values of the 12 bronzes are listed in Table 7.
| Cultural relic number | Incomplete area ratio | Crack length ratio | Corrosion area ratio | Resistance | Hardness |
|---|---|---|---|---|---|
| K7-1 bronzes human figure | 0.0489 | 0.0000 | 0.0000 | 0.0026 | 0.7750 |
| K7-2 bronzes | 1.0000 | 1.0000 | 0.4444 | 0.5084 | 1.0000 |
| K7-3 bronzes bird | 1.0000 | 1.0000 | 0.0278 | 0.0000 | 0.7645 |
| K7-4 bronzes human face | 0.0990 | 0.0141 | 1.0000 | 0.3213 | 0.7805 |
| K7-5 bronzes fragment | 0.0000 | 0.0000 | 0.0000 | 0.0598 | 0.0000 |
| K8-1 bronzes mythical beast | 1.0000 | 1.0000 | 1.0000 | 1.0000 | 0.9820 |
| K8-2 bronzes scorpion | 0.0067 | 0.0015 | 0.0278 | 0.1419 | 0.7426 |
| K8-3 bronzes mythical beast | 1.0000 | 1.0000 | 0.2361 | 0.0038 | 0.9649 |
| K8-4 bronzes human figure | 1.0000 | 1.0000 | 0.6296 | 0.8455 | 0.9573 |
| K8-5 bronzes zun | 0.0883 | 0.0034 | 1.0000 | 0.1994 | 0.7962 |
| K8-6 bronzes zun | 0.0009 | 0.0090 | 0.0000 | 0.1127 | 0.9289 |
| K8-7 bronzes human figure | 0.0051 | 1.0000 | 0.0000 | 0.0559 | 0.9289 |
| Cultural relic number | Health value | Cultural relic number | Health value |
|---|---|---|---|
| K7-1 bronzes human figure | 19.62 | K8-2 bronzes scorpion | 20.49 |
| K7-2 bronzes | 85.40 | K8-3 bronzes mythical beast | 74.29 |
| K7-3 bronzes bird | 66.71 | K8-4 bronzes human figure | 91.84 |
| K7-4 bronzes human face | 38.93 | K8-5 bronzes zun | 36.96 |
| K7-5 bronzes fragment | 0.90 | K8-6 bronzes zun | 24.25 |
| K8-1 bronzes mythical beast | 99.57 | K8-7 bronzes human figure | 51.23 |
Since there is no standard for the health level of bronzes unearthed at present, this paper uses 25 as the tolerance to classify according to the arithmetic sequence. According to the on-site judgment and the mutual verification of the health results of the 12 bronzes, the corresponding health grades were preliminarily obtained, as shown in Table 8. Among them, "Ⅰ" means that the health status of bronzes is in danger; "Ⅱ" means that the bronzes are in a relatively dangerous state; "Ⅲ" means that the bronzes are in good condition; "Ⅳ" means that the bronzes are in excellent health state.
| Range of health | Health level |
|---|---|
| [0–25.00) | Ⅰ |
| [25.00–50.00) | Ⅱ |
| [50–75) | Ⅲ |
| [75–100) | Ⅳ |
| According to Table 7 and Table 8, the health grades of 12 bronzes are obtained, as shown in Table 9. | |
| Cultural relic number | Health level | Cultural relic number | Health level |
|---|---|---|---|
| K7-1 bronzes human figure | Ⅰ | K8-2 bronzes scorpion | Ⅰ |
| K7-2 bronzes | Ⅳ | K8-3 bronzes mythical beast | Ⅲ |
| K7-3 bronzes bird | Ⅲ | K8-4 bronzes human figure | Ⅳ |
| K7-4 bronzes human face | Ⅱ | K8-5 bronzes zun | Ⅱ |
| K7-5 bronzes fragment | Ⅰ | K8-6 bronzes zun | Ⅰ |
| K8-1 bronzes mythical beast | Ⅳ | K8-7 bronzes human figure | Ⅲ |
A health radar chart was then drawn using the data in Table 6, as shown in Fig. 3. The health level of cultural relics was evaluated according to the area of the radar map. The larger the area of the radar map, the better the health status of the cultural relics. The radar chart can intuitively reflect the health of bronzes, help cultural relic workers to understand the health status and existing defects of cultural relics in a timely manner, and provide an important basis for the extraction, packaging and transportation of cultural relics.
The bronzes of health level I are K7-1 bronzes human figure, K7-5 bronzes fragment, K8-2 bronzes scorpion, K8-6 bronzes zun; the bronzes of health level II are K7-4 bronzes human face, K8-5 bronzes zun; the bronzes of health level III are K7-3 bronzes bird, K8-3 bronzes mythical beast, K8-7 bronzes human figure; bronzes with health level IV include K7-2 bronzes, K8-1 bronzes mythical beast, and K8-4 bronzes human figure.
According to the health degree of 12 bronzes and the results of on-site judgment, the corresponding range of health degree and health grade has been preliminarily obtained, which has certain guiding significance. In the future, with the expansion of evaluation objects and data volume, the corresponding range of health degree and health level will be continuously calibrated.
According to the reference index of the occurrence environment, the salinity of K7 is 117mg/L and the electrical conductivity is 213us/cm; the salinity of K8 is 165mg/L and the electrical conductivity is 301us/cm. Taking the electrical conductivity > 166ms/m, the soil belongs to saline-alkali soil as the standard. The salinity of the sacrificial pits K7 and K8 is relatively low, so that the corrosion effect of the cultural relics is relatively weak. But in fact, most of the bronzes unearthed in the sacrificial pits K7 and K8 are relatively thickly rusted, which may be related to the unique burial method that the bronzes unearthed in the sacrificial pits K7 and K8 are covered with a large amount of ivory.
For the first time, the constructed health evaluation method was applied to the Bronzes unearthed at the Sanxingdui site, which not only verified the feasibility of the evaluation method, but also provided an important reference value for future related research.
In view of the current situation lack of health assessment methods for bronzes unearthed from archaeological sites in the field of cultural relics protection, the relevant research results were sorted out. According to industry standards and scientific research results, a framework of health evaluation indexes for bronzes unearthed is established for the first time, which is applicable to the health status evaluation of bronzes unearthed.
In terms of evaluation methods, analysis methods such as Analytic Hierarchy Process (AHP), Entropy Weight Method, Fuzzy Comprehensive Evaluation Method and Grey Relation Analysis (GRA) are often used in evaluation cases inside and outside the industry. Among them, AHP and GRA are suitable for multi-factor health evaluation, and the combination of the two methods can integrate subjective and objective evaluation, making the evaluation results more scientific and objective. Therefore, this paper adopts the combination of analytic hierarchy process and grey relational degree method. This evaluation method can effectively obtain the weight of the health evaluation index of bronzes unearthed.
In the repeated tests in the laboratory and at the archaeological site, in order to quantify the indexes, the DL9810 fiberglass tape measure, resistance meter, LXD-A hardness tester and soil detector were finally selected. These in-situ nondestructive analysis methods are suitable for the complex environment of archaeological sites and meet the needs of cultural relics. In the later stage, the environmental influence factors of the unearthed bronzes will be further analyzed and studied.
The health evaluation method of Bronzes unearthed at the archaeological site was established for the first time. The evaluation method includes the establishment of a three-level index framework for the health evaluation of bronzes unearthed, a systematic in-situ non-destructive analysis method, and the determination of the health evaluation method based on the analytic hierarchy process and the Grey Relational Analysis method.
The constructed evaluation method is used to evaluate 12 bronzes unearthed from sacrificial pits K7 and K8 in Sanxingdui sacrificial area. The evaluation results show that the constructed health evaluation method is feasible, it can reflect the health of the measured bronzes, help cultural relic workers to understand the health status and existing defects of cultural relics in time, and provide an important basis for the extraction, packaging and transportation of cultural relics.
Diseases of bronze collection
Availability of data and materials
In this work, the original data are shown in the main manuscript, and any other further data are available upon request from the authors.
Competing interests
The authors declare that they have no competing interests. We declare that we do not have any commercial or associative interest that represents a competing interest in connection with the work submitted.
Funding
This work was supported by the National Key R&D Program of China [grant number 2019YFC1520100], sub-project: [grant number 2019YFC1530103]. Also this work was supported by Sichuan Provincial Science and Technology Plan Project "Key Technology and Application Demonstration of Archaeological Protection of unearthed fragile Cultural Relics"[grant number.: 2022YFS0558].
Author’s contributions
LL, JX, and JL designed the study. LL, JX, and JL conducted the research. LL, JX, JL, ZX and QX prepared all the data. LL and JL analyzed the data. JL wrote the main manuscript. XL, LL, and XZ revised the main manuscript. All authors read and approved the final manuscript.
Acknowledgements
The authors would like to thank the Shaanxi Academy of Archaeology for supporting this study, Dr. Jianxi Li and Dr. Zhenzhen Ma for helpful suggestions on this study. The authors would like to thank Shaohua Dong for assistance with data collection,whom is from Shaanxi Institute for the Preservation of Cultural Heritage.The authors would like to acknowledge the SiChuan Provincial Cultural Relics and Archeology Research Institute for supporting this study.
Corresponding author
Correspondence to Li Li.
Author email
Juan Li: [email protected]
Li Li: [email protected]
Zhenbin Xie: [email protected]
Jiankai Xiang: [email protected]
Xichen Zhao: [email protected]
Qing Xiao: [email protected]
Xue Ling: [email protected]