Abstract: The microscopic phase and composition analysis of some cast copper relics excavated at the Xingyang Guanzhuang site in recent years, the copper slag blocks are all bronze smelting slag, the products are mainly lead tin bronze, and the tin content of some samples is low, which is closely the same as the alloy technology of bronzes of the central plains princely states in the early Spring and Autumn Period. Most of the smelting slag and bronze ware of the Guanzhuang site have consistent lead isotope ratios with the same pure lead blocks; a few examples of the earliest and latest stages of copper casting production are consistent with the lead isotope ratio characteristics of Fufeng Lijia and Xinzheng Zhonghang Copper Casting Workshop, respectively, filling the missing rings in the metal resource sequence in the early Spring and Autumn Period. The comprehensive alloy technology, lead material resources and reported modeling technology can preliminarily discuss the changes in the technology and resources of copper casting workshops in the early and middle period of spring and autumn.
Located in the west of Guanzhuang Village, Gaocun Township, Xingyang City, Henan Province, the ruins of Guanzhuang are mainly a two-week period city site, and a bronze workshop from the Spring and Autumn Period has been found in the northern part of the city. Since 2018, the School of History of Zhengzhou University has cooperated with the School of Archaeology and Literature of Peking University and other units to conduct scientific analysis and research on a variety of cast copper relics excavated from the Guanzhuang site. In this paper, the composition and lead isotope ratios of metal-containing samples such as copper slag blocks and bronzes obtained from excavations in 2015-2018 are mainly analyzed.
First, the sample situation and analysis results
A total of 34 samples were analyzed this time, and the sample information is listed in Table 1. Among them, there are 26 pieces of cast copper relics, including 10 samples of furnace wall (crucible wall), 16 samples of metal slag blocks, 8 pieces of bronze samples, including 1 piece of tools such as knife and hammer, 2 pieces of empty first cloth currency, and 4 pieces of copper fragments of different thicknesses.
The sample was observed by HitachiTM3030 ultra-depth-of-field electron microscope of the Science and Technology Archaeology Laboratory of Peking University, and the composition analysis was carried out by SEM-EDS (Scanning Electron Microscopy Combined Energy Spectroscopy), the signal acquisition time was 90 seconds, and the results were listed in Tables 2 to 4 in the form of elemental mass fractions. The sample was dissolved in aqua regia, diluted with Tr2SO4 solution as the internal standard, and the lead isotope ratio was determined by using the VGAxiom MC-ICP-MS (Multi-channel Receiving-Inductively Coupled Plasma Mass Spectrometer) of the School of Earth and Space Sciences of Peking University, and the ratio error between 207Pb/206Pb and 208Pb/206Pb was not higher than 0.05%, and the results were listed in Table 5.
Second, the analysis and research of alloy technology
(1) Judgment of the nature of the copper slag block
Some of the cast copper relics excavated from the Guanzhuang site can be determined by macroscopic morphology, such as pottery fan is related to the model making and casting process, and the furnace wall (crucible wall) adhering to copper slag (Fig. 1) is related to the process of refining coarse copper or smelting bronze, while some relics need to be confirmed by microscopic morphological observation and phase analysis. Copper slag and copper blocks have a variety of morphologies (Figure 2), and naked eye observation alone may not be able to accurately distinguish the copper blocks adhering to the melted scum from the naturally rusted metal blocks. If a specific phase produced by the high temperature process can be found on the surface of copper slag and copper block, it can be more accurately determined to be a refining or smelting product.
Most of the copper slag and copper blocks excavated from the Guanzhuang site have a phase produced by high temperature activity on the surface of the sample, indicating a strong oxidation atmosphere, which can be determined as the slag block produced when smelting bronze. Zhou Wenli's smelting slag of the lead-tin bronze system is summarized and discriminated according to the copper, tin and lead phases, and this paper is further sorted out into the following three categories:
1. Tin-containing phase: including cassiterite particles with a square or strip shape (Figure 3); tin-containing calcium (iron) silicate, mostly cytogenic (Figure 4); 2. Lead-containing phase: including lead silicate, often in a uniform glassy state with multiple porosity, and a shell-like fracture can be seen on the surface (Figure 5); 3. Copper-containing phase: including copper oxides, mostly square, often segregation dendrites in an oxygen-rich environment (Figure 5).
During the high temperature process, the metal tin is oxidized to form a self-shaped cassiterite, but a large amount of ash is often produced during smelting, resulting in a high local calcium content, thus precipitating the tin-rich and iron-rich phases, so the first type often coexists in multiple phases (Figure 6). Accordingly, the smelting object can be inferred from the phase of the slag, and the information is summarized in the last column of Table 1.
Most of the copper slag blocks at the Guanzhuang site are bronze alloy slag blocks, most of which are lead tin bronze, a few are tin bronze, and no pure copper, tin and other metal elemental raw material ingots are found, and only a small lead block with bronze inside was found. Among the copper slag blocks tested this time, no pure copper blocks and crude copper refining slag were found, and only a small number of copper particles were found in samples such as H1341:2 and H1573:7, reflecting that the copper casting workshop was alloyed with pure copper, but copper, tin and other cast copper raw materials were centrally managed and not abandoned at will. Guanzhuang H1863 unearthed a metal block (Figure 7), the surface is grayish white, the interior is gray-green, the surface layer is analyzed as lead, containing As0.8%, and the innermost layer is lead tin bronze. Lead ingots found in copper casting workshops during the Shang and Zhou dynasties in the Central Plains often have green color in parts or interiors, such as lead ingots in the north of Liujiazhuang, Yin Ruins in Anyang. The copper content of the lead ingots produced by H329, a copper casting workshop in Houma Niucun, Shanxi, is even more than 10%, and the researchers speculate that the high melting point copper-rich phase is precipitated when the lead bronze ingots are condensed, which should be a by-product of the production of cast copper.
Some broken copper pieces excavated from the Guanzhuang site, varying in size, uneven thickness and thickness, and mostly co-emerged with smelting slag and furnace wall blocks, which may be metal raw materials to be remelted. H1573:15 Copper sheets with a wall thickness of 0.5 cm and a very small curvature, partial remnants of cast ornamentation (Fig. 8), which may be fragments of large ceremonial containers. This fragment and the copper slag block with the same output have similar composition (table 3 row 450114-1 and table 4450114-2 line), and both have iron-rich material characteristics, which does not exclude the possibility that the copper slag block and the copper fragment correspond to the same piece of artifact.
(ii) The alloy composition of the copper block and the bronze ware
At the time of two weeks, the material of bronze containers in the Central Plains has changed significantly. Since the middle and late Western Zhou Dynasty, the number of tin bronze containers that have prevailed has decreased rapidly, and the containers made of lead tin bronze have quickly become mainstream. Thin flake decorations other than containers and some carriage and horse tools, weapons due to the need for mechanical properties for processing and use, are still mostly made of tin bronze or low-lead lead tin bronze. With this background, we can better understand the alloy technology of the Guanzhuang copper casting workshop.
The copper blocks and bronzes excavated from the Guanzhuang site are mainly made of lead tin bronze. Of the 34 samples analyzed this time, only 5 samples were made of tin bronze, and 4 of them were produced with lead-tin bronze blocks or furnace walls, which showed that the same area could produce bronze of different materials at the same time. Among the 5 pieces of copper fragments excavated at the site, 2 pieces are tin bronze fragments, so it can be inferred that the cast copper workshop constantly remelts the tin bronze fragments for reuse, but the alloyed products are mainly lead tin bronze, and only a small amount is tin bronze.
Low-tin bronzes, common in the early spring and autumn, are often seen in the Ruins of Guanzhuang. In the early Spring and Autumn Period, tombs in the Central Plains and Guanzhong regions often buried bronze containers with low tin content. In cemeteries such as Nanyang XiaYupu, groups of red copper or lead bronze containers are even buried. The H1337 copper sheet and T1711-3:8 copper block of the Guanzhuang site are all low tin materials, which can be seen that low tin artifacts were also common in central Henan at that time, and were indeed an important production category for copper casting workshops. There are a large number of low-tin lead-tin bronze and even lead bronze particles in the copper blocks and furnace walls produced by Guanzhuang, but this mainly indicates an insufficient melting process and may not be used to infer the alloy ratio of castings. Li Yanxiang pointed out that the composition of the melting slag is usually very uneven, and the strong oxidation atmosphere during smelting will cause the tin content of the alloy phase in the scum to be lower than the ideal alloy ratio.
In the early and middle spring and autumn periods, the iron content in bronzes is common, and some copper blocks and bronzes at the Guanzhuang site also have this material feature. From the Western Zhou Dynasty to the early Spring and Autumn Period, sulfide copper ore in the middle and lower reaches of the Yangtze River was the main source of copper, and the characteristics of the source led to a high iron content in crude copper. Guanzhuang H1337 copper sheet contains Fe or even as much as 3%. During this period, some metal materials contained relatively high arsenic content, such as T1411-2:11 slag containing As0.8%; New Zheng Gaolou M139:1 Ding contained As1.1%, which was the same period as Guanzhuang Spring and Autumn Cast Copper Relics. From the Guanzhuang H1863 metal block analyzed this time, it is known that the arsenic in the bronze is not only introduced by copper, but may also come from lead containing arsenic.
Third, the change of metal resources
(i) The law of change in the isotope ratio of lead over time
The lead isotope ratios of bronzes and cast bronze relics at the Guanzhuang site have high commonality, and show more completely the changes of the main lead materials from the two-week period to the middle of the Spring and Autumn Period. For the purpose of discussion, 208Pb/206Pb is used as a plot of 207Pb/206Pb, and the empirical reference line l:y=1.6162x+0.7288 is divided into areas, and the ratio between 2.12 and 2.14 in the middle l and 208Pb/206Pb is recorded as Class A, the ratio of 208Pb/206Pb between 2.09 and 2.12 is recorded as Class B, and the ratio of 208Pb/206Pb between 2.15 and 2.18 is recorded as Class C. In the class B ratio, those distributed along the left end of the reference line l are recorded as class B, and those below l are recorded as class B1. In the late Western Zhou Dynasty, the materials of bronzes in the Central Plains were mainly tin bronze and low-lead lead tin bronze, and the distribution of lead isotope ratios was relatively scattered, including A, B, B1 three categories. In the early Spring and Autumn Period, the lead content of bronzes in the Central Plains increased, the lead isotope ratio tended to be concentrated, the Class A ratio became the mainstream, and there was a certain proportion of B1 class ratio in individual areas; since the middle of the Spring and Autumn Period, the proportion of Class B has increased rapidly, replacing Class A as the main lead material category.
Of the 25 lead isotope samples analyzed at the Guanzhuang site, 20 belong to the class A ratio, accounting for 80%, which is the most important ratio category of Guanzhuang; the remaining 5 samples belong to the ratio of B and C, of which the fragments of the container produced by H1573 belong to class B1, and the two empty first cloth samples are B and C, which are discussed separately below. The lead content of the 20 Class A samples varied, with H1337 copper containing less than 0.2% lead, the remaining samples containing lead above 1%, and the H1863 metal block being nearly pure lead. Samples with different lead content have substantially the same ratio, reflecting that the ratio is independent of the lead content of the sample, and it is speculated that the copper and lead sources indicated by the analogue A ratio may be the same, or a class of copper-lead symbiotic mines.
The ratio of unit samples in the first phase of the Guanzhuang Copper Casting Workshop is mainly class A, with individual classes B1. The briefing on the Guanzhuang site pointed out that the pottery bean handles produced by the first phase of the workshop had convex hoops, and the theme of the pottery vessel fan was mainly plagiarism and heavy ring pattern, and the absolute age was the early Spring and Autumn Period. The typical units in this period, such as H1966, are decorated with double-week heavy ring patterns, which have the legacy of the late Western Zhou Dynasty; they also include H1573, H1341 and other units. Of the four samples from the three ash pits, three indicate melting activities and copper casting products are Class A, and the container fragments of H1573 are Class B1.
The B1 analogue value seen in Guanzhuang has a clear geographical origin, and the older resource characteristics are indicated at the Guanzhuang site. The B1 analogue is the lead material resources mainly used in the lower reaches of the Yangtze River from the middle and late Western Zhou Dynasty to the early Spring and Autumn Period (Figure 9), and it can be seen from Wang Kai's analysis of the smelting and casting relics at the Site of Shigudun in Tongling, Anhui Province, that the B1 analogue samples include pure lead samples and copper smelting slag with very low lead content, so it corresponds to a class of copper-lead symbiosis resources. In the late Western Zhou Dynasty, such ratios accounted for a certain proportion of bronzes in Guanzhong and Jinnan; in more eastern regions such as Yuzhong and Shandong, according to available data, such ratios were even the main categories. The discovery of the Guanzhuang site at this stage can show that the metal resources from the Jianghuai region still have a small number of applications in the Central Plains in the early spring and autumn years, and the ratio distribution of the samples in the first phase of the Guanzhuang Copper Casting Workshop is closest to the bronze groups such as Quwo Sheep Tongue M4, Qucun M5189, and Yuguo M2001 (Figure 10). Xingyang was the choke point of southern Jin and western Henan to the Jianghuai region, which mainly used class A lead materials in the early spring and autumn, while continuing to supplement B1 lead, which helped to understand the copper trade between jin and jianghuai regions contained in jinwen materials such as Jin Jiangding and Rong Sheng zhong.
The ratio of the unit samples of the second phase of the Guanzhuang Copper Casting Workshop, except for the empty first cloth, is all Class A ratio. The second phase of the cast copper workshop unit excavated the pottery bean handle department to omit the convex hoop, occasionally saw the arc plate bean, the shape of the instrument is slightly later than the first period, but it is not seen in the middle and late Spring and Autumn units of the Xinzheng Zhonghang site from the drum shoulder pottery bowl, thin high-handled pottery bean and other vessel shapes, the age is obviously earlier than the latter. In this issue, the pottery fan ornaments appear with dragon patterns, conjoined dragon and phoenix patterns, etc., and the fine crab patterns popular in the Zhonghang ruins stage are not yet seen. The typical unit of this issue is H1187, and the absolute age is roughly the early spring and autumn period. The 3 samples tested by H1187 were all class A and were significantly more concentrated than the ratio range of the first phase of the copper casting workshop. According to the current data, most of the lead isotope ratios of bronzes in the Central Plains and neighboring areas from the late spring and autumn period to the early spring and autumn period are mostly class A, and they are equally highly concentrated (Figure 11).
The large number of Class A lead materials used in the Guanzhuang site are still difficult to determine the specific source of production, and the southeastern Hubei-northern Ganbei region is the most likely, but there is still a lack of evidence of lead-related mining and metallurgical relics. Guanzhuang H1861 lead block is the first time in the cast copper site found in the physical object of class A lead, its internal composition is uneven, wrapped in a small amount of bronze, indicating that it is related to copper casting activities, rather than small lead ware, this lead block arsenic-rich, silver trace element characteristics are also of great significance to summarize the materialological characteristics of such lead raw materials.
(ii) The age of the empty first cloth and related monuments
A number of empty cloth and cloth mud cores have been excavated from the Guanzhuang site. Of the two empty first cloth samples that have been measured so far, the lead isotope ratio indicates the meaning of a later age, and the upper limit is not earlier than the units such as H1187 in the second phase of the workshop. The lead isotope ratio of Guanzhuang H1828 empty first cloth is Class B. This kind of ratio is gradually popular in the Hanhuai region in the early and middle spring and autumn periods, and is the most important lead resource in the Central Plains and Haidai regions in the middle and late spring and autumn periods, and is currently the earliest seen in the M42 and M100 of Xinghong Garden in Zhengdi, and is also the ratio type of smelting slag in the late spring and autumn period of the BOC copper casting site (Figure 12).
The isotope ratio of lead in Guanzhuang T1712-2 is C, which has a clear chronological upper limit in the Central Plains. The earliest example of Class C lead in zhengguo bronzes is the new Zheng Zhonghang sacrificial pit K2 Ding, while the earlier Xinghong Garden M100 Dunshang is class B; in the Bronze ware of the Jin Dynasty, the earliest class C lead is found in the M21 of Wayaopo in Yunxian County, while the earlier Wayaopo M30 and M29 are still class B; the earliest class C lead in Haidai area is found in the M152 of Xue Gucheng in Tengzhou, while the earlier Zaozhuang Xulou M1 and Changqing Xianrentai M5 are all class B; the earliest class C lead in Chudi is found in Yunyang Qiaojiayuan M4, but class B lead has been used until the Warring States. It can be clearly seen from this that the upper age limit of C-class lead in the Central Plains during the Spring and Autumn Period was roughly 580 BC to 570 BC. It is difficult for the empty head of the Guanzhuang C analogy to be earlier than this.
The Guanzhuang site has cast copper remains with empty first cloth, which is roughly at the same time as the new Zhengzhonghang copper casting site, or it may be considered to be separated from units such as H1187 and separately classified as the third phase of the copper casting workshop. The shape of the empty first cloth of Guanzhuang is all shrugged shoulders arc crotch pointed foot cloth, which is obviously different from the flat shoulder cloth seen in Xinzheng Zhonghang and other places, and is very similar to the large empty first cloth before and after the late Spring and Autumn period of Jindi. The border between Jin and Zheng began in the year when Duke Wen of Jin received Nanyang Di (635 BC) from the Zhou Dynasty, which was also a rough chronological upper limit for the first cloth of the Guanzhuang Kong. The H1828 of the empty first cloth excavated from Guanzhuang broke the H2496 of the excavated spear core, and it is known that such ash pits related to the production and use of the empty first cloth are later than the remains of the early cast copper in Guanzhuang in terms of stratigraphic relations. The ash pits with the first cloth brass cores such as H2032 also have a trowel model, knowing that the production of cast copper in this period still has a certain scale, and the products are relatively diverse, not limited to currency. The copper block from Guanzhuang H1819, the ratio is also class B, may also belong to this stage. A series of ash pit units, such as H1886 and H2037 that break H2032, and H1785, which break H1828, can provide a more accurate reference for the lower age limit of this stage.
4. Preliminary analysis of the diachronic changes in copper casting technology and metal resources at the Guanzhuang site
The guanzhuang site has a large number of cast copper relics excavated in recent years, with rich types and continuous chronology, which can initially fill the technical and resource deficiencies between the Li family copper casting workshop in the middle and late Zhou Dynasty and the Xinzheng Zhonghang copper casting workshop in the middle and late Spring and Autumn Period. Han Yu and Liu Siran of the University of Science and Technology Beijing systematically analyzed the production technology of the pottery fan excavated from Guanzhuang, and preliminarily summarized the changes in the technical characteristics of the production method, the particle size of the model material and the baking temperature from the typical units of the two phases. Model-making technology and the alloy technology discussed in this article are two important aspects of copper casting technology, and the diachronic observation of these two types of technologies and lead resources and other factors is helpful for in-depth study of the changes in copper casting workshops.
The alloy technology and lead resources of the first phase of the Guanzhuang Copper Casting Workshop have undergone great changes from the late Western Zhou Dynasty, and the modeling technology and ornamentation style are in line with the Western Zhou Dynasty. In this period, lead tin bronze was changed to the main product category, and the lead material from the lower Reaches of the Yangtze River was drastically reduced. Compared with the tao fan unearthed by the Li family, the silt particle size of the Guanzhuang tao fan has increased, but the relevant technology of making the model still has a high similarity.
The alloy technology and lead resources of the second phase of the Guanzhuang Copper Casting Workshop have changed little from the previous period, while the modeling technology and ornamentation style have changed significantly. Han Yu and Liu Siran pointed out that the production technology of the pattern decoration fan changed in the first and second periods of the workshop, from the model to the imitation of the pattern; the fan surface is no longer finely operated, resulting in the gradual change of the particle size of the fan material from delicate to rough; at the same time, the large increase in the prefabricated pattern mold leads to the need to enhance the mechanical properties of the pottery fan to cope with frequent handling and storage, which promotes a significant increase in the temperature of the baking model. The pottery fan production technology of the third phase of the Guanzhuang Copper Casting Workshop has not yet been reported, but from the macroscopic morphological observation, it should be relatively close to the pottery fan of the second phase of the workshop. The pottery fan of the Spring and Autumn Stage of the Xinzheng Zhonghang Site is basically equivalent to the current period, and Liu Siran has conducted a systematic analysis of material and particle size, and the particle size of the silt is slightly higher than that of the second phase of the Guanzhuang Workshop. In the process of the stable development of alloying and model-making technology in this issue, the change of lead materials is very obvious, and two new types of lead material resources have been applied (Figure 13).
From the scientific and technological analysis and research of the Guanzhuang site, it can be found that the evolution of the technology and resources of the bronze casting site is not necessarily synchronized, and has different degrees of influence on the changes in the decorative style of bronze (Table 6). Tao Fan is the physical carrier of ornamentation, so the evolution of bronze ornamentation style is relatively closely related to the model-making technology. Alloy ratio can determine the fluidity of copper liquid, low tin alloy ratio often limits the degree of refinement of the ornament, so the decorative style of the utensils and the alloy material also have a certain relationship. However, in addition to considering technical factors, alloy technology is more affected by the abundance of metal resources, and metals, especially precious tin, are strongly affected by trade routes and political patterns. The decrease in the tin content of bronzes in the Central Plains in the early spring and autumn is likely to be related to the drastic changes in the political environment at the time of two weeks; the re-increase in the tin content of bronzes from south to north in the middle of the Spring and Autumn Period, the extensive application of lead and tin resources corresponding to the B analogy, and the historical facts of the northward advance of the Chu state are also basically consistent with the historical facts of the northward advance of the Chu state. Therefore, the metal resources and alloy technology of copper casting workshops in the Spring and Autumn Period are closely related to the political and economic interaction between countries, and when conducting research on one country and one place, it is also necessary to grasp the commonality of the times.
5. Summary
The cast copper relics excavated from the Xingyang Guanzhuang site are a good entry point for studying the bronze style and copper casting technology from the Western Zhou Dynasty to the Spring and Autumn Period. After the eastward relocation of the Zhou Dynasty, the alloy technology and metal resource network between the princely states in the Central Plains showed strong consistency and were closely related. The alloy technology and lead material resources reflected in the Guanzhuang ruins are consistent with the technology and resources of bronzes in the Central Plains in the early and middle Spring and Autumn Period, so at this stage when there are still no examples of copper casting sites, the Guanzhuang ruins can be used as a typical copper casting workshop of the Central Plains princely states in the early and middle Spring and Autumn Period, and used to construct and improve the evolution sequence of various types of copper casting technologies and resources centered on the Central Plains in the pre-Qin period.
The copper slag blocks excavated from the Guanzhuang site can be judged from the specific phases indicating high temperature such as cassiterite, tin calcium silicate, lead silicate, etc. It can be judged that most of them are bronze smelting slag, and the products are mainly lead tin bronze. The lead blocks and cast copper relics found in Guanzhuang and the lead isotope ratio are mainly class A, reflecting the continuity of lead resources in the booming stage of copper casting activities at the Guanzhuang site. The first phase of the Guanzhuang Copper Casting Workshop is still remelting in a small amount of metal resources with the common B1 analogue value in the earlier stage, and after the second phase of the workshop, it has begun to use the common B and C lead materials in the middle and late Spring and Autumn Period, which fully reflects the diachronic changes in the use of lead resources in the Spring and Autumn Period in the Central Plains. If we can conduct a more comprehensive analysis of the cast copper relics excavated from the Guanzhuang site, and take into account the relevant information of the bronzes excavated from the Spring and Autumn Tombs of Guanzhuang, we can further clarify the characteristics of the times.
Through the observation of the technology and resources of alloy preparation and pottery fan production, a preliminary understanding of the copper casting technology of the Guanzhuang site has been formed. The various technologies and resources do not change synchronously, and there are different ways of correlating with the evolution of bronze styles. Changes in lead material categories and alloy ratios indicate the degree of abundance of metal resources, which are clearly influenced by the political landscape due to the separation of copper casting workshops from metal sources. In the Spring and Autumn Period, powerful princely states participated in the struggle for hegemony and formed a political order through the way of alliances, which may also assume the function of distribution and transmission at the resource level, resulting in the synchronous change of the commonality and diachronic nature of the wide-area resources shown by the current bronze detection data; while the modeling link for craftsmen has its own technical logic, the evolution law is more orderly, and directly affects the presentation and transformation of the bronze style.
Acknowledgements: The lead isotope ratio data used in this paper were determined by Associate Professor Huang Baoling of the School of Earth and Space Sciences of Peking University, Associate Professor Liu Siran of the Institute of Science and Technology History and Cultural Heritage of the University of Science and Technology Beijing, and Lin Shirui, a doctoral student at the School of Archaeology and Culture of Peking University, provided important opinions on the research of this paper.