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.