Text: Xiao Peng's brilliant notes
Editor|Xiao Peng's brilliant notes
[Preface]
Hengyang, Chenzhou and Yongzhou in southern Hunan, also known as the Southern Chu region, are often heard of as the land of the cangwu.
Probably during the Spring and Autumn Period and the Warring States Period, the power of the Chu State expanded to the south of Hunan, and the Southern Chu region bordering Lingnan became the southern boundary of Chu culture.
Some professional scholars have proposed that some of the copper tripods in southern Hunan are flat-legged and edged, showing the factor of Vietnamese-style tripods, which should be derived from the continuation of the traditions of the indigenous people themselves in the new period.
The categories of bronze swords include the flat-stemmed and unused short swords, which are different from the double-hoop swords commonly found in Chu, and the burial tools that accompany the burial sites also appear in the original bronze tools popular among the Yue people, such as curved blade axes and scrapers.
Most of the bronze mirrors in the Southern Chu region are common Warring States Chu mirrors such as feather-patterned mountain mirrors, four-leaf mirrors, and diamond-shaped mirrors, but a few bronze ornaments are very different.
Therefore, the bronze typology of the Southern Chu region has a high consistency with other regions of the Chu region, and it also has a certain local tradition.
In the previous research results of the Chu bronzes of the Warring States Period, the metallurgical analysis of the bronzes unearthed from the Chu tombs in different locations has clearly revealed the complex and mature bronze technology of the Chu State.
Specifically, the stable formula control of different types of bronze ware according to mechanical properties, as well as the production technology of Pingbi bronze ware, the previous analysis cases were mostly concentrated in Jiangling, Xiangyang, Yicheng Zaoyang and other places in the core of Chu in the Warring States period.
Metallurgical analysis has also provided a new understanding of the local Chu bronzes in the area south of the core area of Chu and in the area around Dongting Lake, but no attention has been paid to the southern Chu area south of the Dongting Lake area.
The study of the bronzes of the Southern Chu region and related Chu Mu is not only helpful for understanding the historical process of the southward expansion of the Chu state, but also helps to further understand the technology of the bronzes of the Chu state.
This shows that the production and circulation mechanism behind the highly unified style is seen in the places within the Chu State, and the archaeological work in Chenzhou and Hengyang in Southern Chu has found a large number of Chu tombs, and has also accumulated certain bronze materials.
Then, on the basis of the sorting of Chenzhou bronzes, after systematic sampling and analysis, what new production techniques are further revealed?
【Chenzhou Warring States Bronzes】
The main categories of Chenzhou Warring States bronzes analyzed are weapons, containers and bronze mirrors, a total of 41 pieces, including 17 weapons, including double-hoop swords, composite swords, flat-stemmed swords, copper ge, and copper spears.
The other 12 pieces are copper tripods, including Vietnamese-style tripods and Chu-style tripods and 2 copper pots, the cross-sections of which are mounted, polished and polished to meet the needs of metallographic observation.
Part of the analysis of the Chenzhou area Warring States period bronze photographs
The copper samples were etched with ferric chloride hydrochloric acid solution, and the metallographic structure was observed and photographed by metallographic microscope, and then the scanning electron microscope and energy spectrometer were used to determine the quantitative alloying elements without standard samples with the scanning electron microscope.
【Ingredient Analysis Results】
According to the scanning electron microscope analysis, we can know that among the 41 samples from the Warring States period, except for 6 that cannot be judged due to rust, 15 of them are tin bronze, and the rest belong to lead-tin bronze.
Arsenic was detected in some bronze artifacts, but because of the low proportion, it is likely that the human element carried by the mineral material, rather than the alloy of the intentional human addition, and a very small number of copper artifacts showed a relatively small amount of sulfur.
Other elements that are more common in compositional analysis, such as iron and silver, may not be present in the spectroscopy due to their very low concentrations, so the raw materials of copper artifacts in the Chenzhou area may have a higher degree of refining or remelting.
In tin bronze and lead-tin bronze, the tin ratio is roughly 5.5%~26.0%, but some bronze artifacts are more seriously corroded due to rust and free copper sedimentation, resulting in high tin content in individual bronze test results.
In some past studies, it has been clearly pointed out that the proportion of different types of alloys in ancient Chinese bronzes generally shows a certain pattern.
【Metallographic Organization】
The metallographic structure was then observed, which allowed for a better understanding of the copper fabrication process, and the composition of most of the bronze artifacts in this analysis was in good agreement with the microstructure.
In the samples containing higher tin, the α phases were coarse needle-like or sharp strips at both end δ α s, and the (α+δ) eutectic bodies were connected into a matrix or reticulation.
【Grid-like eutectic organization】
This kind of organization is more common in bronze mirrors, and the metallographic structure of some copper weapons, such as double-hoop swords and spears, appears in large numbers, which are connected into a grid (α+δ) eutectic organization.
Combined with the composition test, these bronzes should be high-tin bronzes with high tin content, and the lead content is generally low in weapons and bronze mirrors.
The lead particles in the bronze ware are small and dispersed between the matrix and the dendritic crystals, on the contrary, due to the metallographic structure with high lead content in the container, a large amount of lead particles are mostly diffused in the matrix, and some of them are lumpy and spherical between the grains.
In addition, there are more sulfide inclusions in the metallographic structure, and holes of different sizes and a large number are more common in the detection, and the cause of the holes is likely to be due to the appearance of insoluble gases such as sulfur monoxide in the solidification stage.
Or because of the holes left by the rust of the lead particles, because the (α+δ) eutectic in tin bronze is relatively fragile, the craftsman needs to heat treat the bronze or then cold work.
It is worth noting that most of the high-tin bronzes still retain the original cast dendrite structure, which is not found in the metallographic structure, and there are clear traces of heat treatment and cold working.
However, in the analysis here, the metallographic photographs of the two pieces of copper Ge show the structure treated by thermal homogenization, and the so-called thermal homogenization refers to the heating of the copper ware at a certain temperature to homogenize the composition to varying degrees.
The tin content detected by the energy spectrum of the copper Ge sample was about 16.7%, the dendritic segregation basically disappeared, the crystal was large-grained, and only 8 phases remained in the (α+δ) phase.
Special attention should be paid to the composite column-stemmed double-hoop sword, which was broken at the time of the sergeant, so a sample could be selected from the section to analyze the mortise and tenon structure.
【Compound Sword】
The so-called composite sword is a mortise and tenon structure that combines the spine of a sword with a low tin and copper and a sword of high tin bronze from two castings to form a bronze sword that combines rigidity and softness.
Due to the different tin content of the sword spine and the two blades, it is also called a two-color sword, according to the analysis of this kind of copper sword in the Shanghai Museum, it can be seen that the composite sword is generally cast first.
It is then embedded in the sword and then cast into the sword body, and the mortise and tenon structure strengthens the union of the two parts, and due to the contraction force generated by the metal when it solidifies, the rod head or part of the sword ridge of the sword spine is enclosed in the sword spine, and the sword spine and the sword spine are thus firmly combined into one.
In the process of baking, the sword ridge is often homogenized annealing heat due to heating, and a coarser dendritic composition appears, and there are fewer eutectic phases between the dendrites.
However, the end of the mortise and tenon structure of the Shangbo composite sword is relatively wide, so it fails to play the role of clamping and stabilizing the sword body and the sword slave as the sample structure of the Shangbo bronze sword, and the metallographic photos also show that the sword and the sword spine are not very closely combined, and there is a large gap between the sword and the sword spine.
In terms of composition, it is different from the composite sword analyzed in Shangbo, the lead content of the sword spine part of the sword is higher, up to 13.3%, and there are many uneven size drill blocks between the grains in the metallographic structure.
The lead content of the sword part is also high, reaching 7.1%, and the lead particles can be seen in the metallographic structure, and the lead content of only one piece of sword reputation is 13.14% in the analysis of Shangbo, and the lead content of the sword part is not higher than 2%.
This shows that among all the bronze artifacts analyzed this time, the tensile strength of composite swords, especially the spine of the sword, is relatively poor.
According to the previous understanding, the bronze composite sword generally first appeared in the Wuyue area, this kind of copper sword that can be combined with different hardness and strength of tin bronze to make "rigidity and softness", which shows the superb alloy technology of smelting and casting technology in the ancient Wuyue area.
A certain number of composite swords were also found in Qi and Chu during the Warring States Period, and three copper composite swords were also tested in the previous analysis of the composition of copper swords unearthed around Jiangling and the Chu tomb in Echeng.
Similar to the test results of Shangbo bronze swords, the swords of composite swords unearthed in Jiangling and Echeng are high-tin bronze with higher strength and hardness, and the spine is low-tin bronze with better toughness, and the ratio of lead in both parts is low.
Because the composite swords seen in Chenzhou have certain differences in mechanical properties compared with the similar composite swords analyzed in Shangbo, Jiangling and Ezhou.
Whether this is due to poor production technology or other reasons for process differences needs to be further analyzed.
[Bronze ware with high individual lead alloy structure]
The metallurgical archaeological analysis of copper weapons and containers in different regions of Chu has accumulated a considerable amount of data, and the detection results of copper artifacts in the southern Chu area of Chenzhou and other regions of Chu have also shown strong commonalities.
Chenzhou bronze ware is dominated by copper-tin and copper-tin-lead alloys, and most of the copperware basically have no or only a small amount of arsenic, and the proportion of tin-lead alloys in different types of copper objects is significantly different.
This is basically in line with the previous understanding of Chudi bronzes, especially the copper mirrors analyzed this time, and the tin content is the highest among the three types of analyzed bronzes.
Eight of the nine samples (α+δ) were predominantly matrix-like and had low lead content, generally less than 5% or no lead in the alloy.
In the past analysis, He Tangkun systematically tested the bronze swords or copper weapons of the Warring States period unearthed in Jiangling and Echeng, and found that the tin content in the copper weapons was about 15%-18%.
The tin content of bronze weapons in the Paomadi Formation in Yicheng area is also close to this, and the average tin content of copper weapons in Chu tombs in Chenzhou is about 20%, roughly between 18%~22%.
Although the corrosion of the samples is more severe and the tin content may be high, except for some short swords, the rest of the weapons samples show large slices (α+δ) in the form of grids or matrices, and thus belong to high tin or tin bronze close to high tin.
In the Huangnihu Formation, which is close to the age, the tin ratio is also higher among the alloys, and in general, the tin content and production technology of the bronze weapons of the Chenzhou Formation are close to those of other comparison groups.
In addition to the weapons unearthed in Zaoyang Jiuliandun are likely to be specially made Ming weapons, the general rule is that the weapons in Chudi are high tin and low lead, and the lead content of copper weapons in Chenzhou is low.
However, the ratio of lead alloy in individual weapons is more special, in addition to the mortise and tenon structure is different from the previous analysis, the lead ratio of the sword is also higher than that of the composite sword with the same part of the current analysis.
However, this phenomenon is not seen in the bronze weapons of the Huangnihu and Paomadi Formations, so the high lead and related poor mechanical properties in some bronze weapons are likely to show the local characteristics of the Warring States bronzes in the Chenzhou area.
The increase of lead will reduce the strength and elongation of bronze alloys, but lead can reduce the friction coefficient of special copper, improve the wear resistance, and cast bronze containers with delicate decoration, thin walls and complex shapes, but have higher requirements for the fluidity and other casting properties of the alloy.
Due to the low melting point of lead and the fact that lead is generally free in alloys, high levels of lead will strongly break the microstructure of copper during the casting process of bronze artifacts, thereby improving the fluidity and filling performance of the molten copper, reducing the probability of defects such as insufficient pouring, and helping to cast ritual vessels with delicate and complex ornamentation.
In the Chenzhou Formation, some copper containers had high lead content, but 6 of the bronze artifacts contained less than 10% lead, and there were no large lead particles in the metal matrix in these samples, so the lead content of the Chenzhou Formation was generally low in the box plot.
A recent analysis of the composition of containers from the Yugang cemetery in Xiangyang found that the lead content was low, generally no more than 10%, and the lead content of Chu-style copper containers seen in Zhongxiang and Liu Yue in Huangmei was also found to be more than 10%.
Zhang Ji et al. have pointed out that the content of lead in copper container alloys in Yugang and other places is quite different from the previous situation found in Zhaojiahu in Dangyang and Qiaojiayuan in the county.
According to the relatively clear metallographic photos in the analysis reports of Happy Horse Embankment and Chen Po, the corresponding block or spherical lead block also appeared in the metallographic structure of copper containers with high lead content in some component detections.
It indicates that the lead content of copper containers in some cemetery materials is indeed high, so whether the difference in lead content in Chudi copper containers will vary according to the differences in workshop traditions needs to be supplemented by more analysis.
In addition, a number of related factors also deserve attention in the future, first of all, because most of the previously analyzed bronze artifacts are seen in the tombs of high-ranking nobles, the variation of lead content cannot be ruled out to be related to the complexity and clarity of the ornamentation of the bronze artifacts themselves or other alloy properties.
[The production technology of Southern Chu and Chu is the same]
The bronze artifacts tested in this test not only have a large number but also basically include most of the bronze categories seen in Chu tombs, and the test results provide a representative batch of new information for the technical and technological characteristics of the Warring States bronzes in the Southern Chu region.
At the same time, it also promotes the understanding of the production of bronze ware in different regions of Chu and even in southern China during the Warring States Period, and the bronzes analyzed this time are mainly tin bronze and lead-tin bronze.
The test results of various copper alloy formulas are very close to those of other local copper wares, showing the consistency of the production technology between Southern Chu and Chudi.
It also shows that the copper industry of Chu as a whole also has strong stability in terms of technology and alloy control, and the production of some bronze artifacts in Chenzhou, such as composite swords, shows a different process technology from similar bronze artifacts in the past, enriching the understanding of the production process of bronze artifacts in the Warring States period.
Although the alloy and production technology of bronze ware are highly consistent with other materials, the alloy ratio of some copper artifacts in the Southern Chu region also shows certain regional characteristics.
Although the existing analytical materials have certain limitations, the raw materials, the requirements of mechanical properties for bronze casting, and the local characteristics of different regional industries are worthy of further exploration in future research.