Figure 1 bronze casting technology (quoted from ancient metal technology in China)
No smelting furnace or slag has ever been found in the copper casting site of Yin Ruins, which shows that the smelting and casting process is carried out in different parts. Therefore, the bronze production process in Anyang does not include ore mining and rough refining in the first grid on the left, but it does not exclude refining. As can be seen from the above figure, before pouring, the process of preparing ceramic mold and melting alloy are carried out at the same time. Let's briefly describe the specific methods of each link (see "Casting Technology of Bronze Ritual Castings in Yin Ruins" to be published in Archaeology, this article is simple).
(A) mold production
1. Selection and preparation of modeling materials
This step is the mud material selection and mud material treatment procedure as shown in figure 1.
In order to understand the selection of molding materials and manufacturing technology of Yin Ruins, it is necessary to scientifically detect the pottery models unearthed from bronze casting sites. So far, among several large-scale copper casting sites found in Yin Ruins, only some pottery molds unearthed in the north of nursery and southeast of Xiaomintan have been verified in detail. The experimental results show that the local clay is used in the pottery mould of Yin Ruins, and it is washed, smelted and aged, and river sand, mussel powder (or other silicate substances), plant materials and other materials are added, mainly to improve the heat resistance and castability of the pottery mould. Comparatively speaking, the core contains more fillers to have better heat resistance and collapsibility. Fan Tao added more clay than pottery, which may be related to the requirements of casting performance. The parting surface of Fan Tao is coated with fine red mud or smoke, which may be a measure to improve the surface quality.
It must be pointed out that what kind of clay to use, underground raw soil or river sedimentary soil, has always been discussed. However, it is difficult to draw a direct conclusion by chemical analysis. At present, the author is cooperating with Professor Jim Stoltman of the University of Wisconsin in the United States to analyze the physical structure of Fan Tao by polarizing microscope, and to understand the selection of raw materials and the addition of materials. In a sense, this approach is more convenient to restore the truth of history. When ancestors transformed materials, the first thing they saw was the change of their physical properties. For example, the main purpose of elutriation is to increase the mud content. Although chemical analysis shows that calcium oxide has decreased, this is not the purpose of the ancients. In other words, it can be proved that modeling materials, especially fabrics, can be cleaned through the phenomenon of decreasing calcium oxide.
2 mold design and manufacture
Mold is usually a closed entity with a cavity inside, which consists of mold, core and core support. The cavity is the shape of the object being cast. The fan forms the appearance of the object, and the core forms the inner cavity, hole and some hollow parts of the object. The combination surface of norm and norm is called parting surface.
The practice of casting molds in Yin Ruins is to cast them with clay, which may be similar to pottery. The shape of the mold is designed according to the needs of making the model. Therefore, molds for larger objects are generally made according to different parts, and unnecessary parts in the overall model will be omitted to save materials and man-hours. There are two ways to make patterns on the mold. One is to stick a piece of mud on the surface and carve patterns on it. One is to shape the outline of the main pattern on the surface of the mold, and then draw the lines of the auxiliary pattern with cinnabar.
Turn the pattern over with a mold and engrave the details of the pattern on the pattern. Some patterns are directly printed or engraved on the patterns, such as? 1? The circular vortex pattern on the shoulder (as shown in Figure 9) can be regarded as the forerunner of the stamping method in Houma period.
Anyang Fan Tao has two ways of doing it, namely, the first-style model named after Li Yongdi and the second-style model. The former has no mortise and tenon, smooth back and only a horizontal or vertical convex edge, which is thin, and may be mainly used in Sanjiazhuang period and Yinxu period. Some of the I-shaped patterns are mostly a group of narrow lines, which may be used by pottery lines embedded outside. Type ⅱ is mainly used after the second phase of Yin Ruins, with uneven back, which refers to the trace of nest pressing, and the parting surface has mortises and mortises.
According to the different shapes and types of bronzes, they are generally divided into vertical and horizontal directions, and the form of division is more complicated, which is detailed in another article. The method of compound model is used to make high relief animal heads, that is, a cavity is left on the physical model, a piece of model mud is put in the groove, animal heads are embossed with live animal heads, or small animal head models are embedded.
Because of the high requirements for fire resistance, yield and collapsibility, the core may be manufactured independently, instead of completely scraping off the wall thickness of the casting with a mold as Zhang Shi said. In particular, the cores of some large vessels are often rammed with coarse sand and soil according to the specifications of different parts. Unearthed cores are generally brick red with loose and rough texture, which is different from exquisite molds. Blind cores of feet and other parts are usually equipped with clay core supports to match the model. The core forming the cavity of the vessel is provided with a core head, and the side of the core head is provided with a tenon, and the center is provided with a groove matched with the bottom die. Most clay cores with inscriptions are reproduced from clay molds, and the reproduced embossed characters need to be carved and trimmed, and clear grooves can be seen next to the strokes of the characters. Its top surface has a matching tenon, which is used to be embedded in the mud core of the object.
3. Drying, baking and assembling of the mould
At present, there are still different opinions on whether the next process of mold making is drying, whole baking after assembly or assembly after baking separately. After assembly, it must be dried again (and preheated at the same time) before pouring. After demoulding, the mold should be naturally dried in a cool place to make the water evaporate slowly and evenly, which is very important to control deformation and ensure its tightness. Small molds may be fired in a fan kiln, and the structure of the kiln is the same as that of a small ceramic kiln. This step focuses on the baking process. Tan Derui once thought that the baking temperature of ceramic fans was higher than 850 degrees. In cooperation with Liu Xinyi, the author thinks that the baking temperature may be only about 600 degrees, which is far lower than the firing temperature of pottery. This is also close to the data of Wan Jiabao restoration experiment.
Most casting models have tenons and mortises on the parting surface to match the mold. Sometimes it is necessary to set a metal iron core bracket between the iron core and the fan.
Large objects need to use the bottom model, and the core and the bottom model are connected together. Some large-scale artifacts directly tamp the bottom template, such as the bottom template of large circular artifacts found in Xiaomintan.
Generally, a tripod has a wheel above its feet, with one foot as the wheel and the other two feet as the air outlet. The runner of the foot winder is also placed on the foot, and the bottom fan will make the runner part.
At this point, the whole mold is made.
(2) Melting and preparation of alloy
This problem is the weak link of the whole casting process research, and basically all the steps are speculation and controversy.
1 Talking about copper smelting equipment
A large number of ceramic fragments fired at high temperature have been unearthed from the copper casting sites of Beidi and Xiaomintun in Nursery, Anyang. Some surfaces have cracks burned at high temperature (Figure 2), some surfaces have been vitrified, and there are traces of mud strips or grass mixed with soil on the back. Scholars in the past thought that this was the residue of the furnace and was heated by internal combustion. The analysis of the fragments unearthed in the north of the nursery shows that there is only a small amount of copper in the other two samples except 1, and there are trace amounts of tin and lead in all three samples.
Fig. 2 Pottery fragments unearthed from the bronze casting site in southeast Xiaomintan (top: front, bottom: back)
The author analyzed two such samples, and found that the content of silica and calcium oxide was higher, especially in the back layer. It is speculated that the raw material of the debris is probably obtained by adding sand and mussel powder to the native soil. The burning loss of the back layer of the sample is large, which means that plant stems and leaves are added, which is made of grass mixed with mud. 1 The calcination temperature of the sample is higher than 900℃. 1 sample contains a small amount of copper slag and contains three elements: copper, tin and lead.
When sorting out a large number of fragments of this "melting pot" unearthed from Xiaomintun copper casting site in Anyang, the author found that most of the fragments were not attached to the surface. Even if it is badly burned, the samples whose surface is close to enamel can't see any traces of metal from the appearance, and only a few pieces have charcoal and metal attached to their surfaces. However, in the copper casting sites in Beidi of Nursery and Xiaomintun, a kind of residue with copper liquid on the surface was generally found, including coarse sand hard pottery and fine sand argillaceous, which was a small piece when unearthed and could not be recovered (Figure 3). Most of these fragments have several lining layers, and each lining layer is stuck with copper liquid, which proves that it has been repaired and used many times. The contact part between the lining and the copper liquid is grayish green, and most of them have been burned into pores and honeycombs. The back is mostly loose braised soil. Liu has mentioned many times that there are smelting slag on many pieces of braised soil, which may be such a relic. The digger in the north of the nursery also thinks it is a crucible-type copper melting tool.
Fig. 3 Crucible fragments unearthed from the southeast copper casting site in Xiaomintun (top: front, bottom: back)
This can't help but ask a question? 1? 7? 1? What is the relationship between the "melting furnace" and "crucible" fragments in the site and metal melting?
The bottom of a smelting furnace was unearthed from the site of early foreign copper casting in Nanguan, Zhengzhou, and the upper part of the furnace body was missing, leaving only a nearly oval pit with a diameter of about 1.60-2.60 meters, which was filled with copper slag, furnace wall blocks, carbon chips, big mouths, crucible pieces and stewed soil blocks. The author speculates that this is a copper melting furnace, and the process of melting copper is to put charcoal first, then put the crucible, and finally burn the fire to melt copper.
Nearly a thousand pieces of "furnace fragments" were unearthed from the bronze casting site of the Western Zhou Dynasty in Beiyao, Luoyang. The surface is cracked or even vitrified, some of them are still stuck with charcoal and copper particles, and there is a furnace ring mixed with grass mud on the back. The so-called "stove" has a pot bottom with two layers of copper slag, which is made of braised clay, very similar to the above crucible fragments. It is hard to imagine that the so-called "hearth" and "furnace ring" with different textures belong to different parts of the same furnace.
Two burning kilns have also been unearthed from the site of copper casting in Beiyao. The kiln wall stands flat, the inner wall is sintered into a fluid state, the outer wall is stewed with soil, the kiln roof is closed with a flat roof, and a cylindrical flue is arranged at the north of the center of the kiln roof (Figure 4). Although the kiln is still a cross-hole raised flame kiln, its combustion chamber and firing chamber are close to horseshoe-shaped semi-inverted flame kiln, and the heating effect is good. The purpose of this kiln is not mentioned in the excavation report, but it is probably related to melting metal, because if it is a roasting kiln, it usually burns several hundred degrees, which is not enough to make the kiln wall burn.
Therefore, Professor Jing Zhichun and Professor Jim Stoltman suggested that the real copper melting vessel may be a crucible, not a ceramic melting furnace. In other words, the crucible is in direct contact with molten metal, and the melting furnace is a device for heating the crucible to meet the pouring requirements as high as 1200- 1300℃. Mr. Barna once imagined such a copper melting apparatus, in which an externally heated large crucible was placed in a ceramic kiln. The copper outlet of the crucible wall was made very thin and connected with the kiln wall with a pipe, so that the pipe was blocked when melting. After the molten copper melts, open the pipeline and pierce the crucible wall with a stick, and the molten copper will be discharged for pouring (Figure 5). Hua Jueming once suspected that the crucible size was too large to ensure the melting of the alloy. If the crucible is punctured, it is difficult to ensure that it will not melt through during the melting process. Despite the above doubts, the author still thinks that this idea is very possible, because it can reach a higher temperature, and it can also explain why many furnace fragments are not attached to the surface of copper liquid, which is likely to be kiln wall fragments. However, because a large amount of copper has also been detected in the combustion layer of ceramic melting furnace fragments, the possibility of using it as a melting furnace cannot be denied.
For this reason, the author and Professor Stoltman extracted a large number of samples respectively. In order to analyze the chemical composition, microstructure and manufacturing method of these two kinds of fragments in detail, Jing Zhichun and Yue Zhanwei set out to carry out restoration experiments in Anyang, and calculated the highest temperature that this kind of kiln furniture can reach for further discussion and in-depth study.
Fig. 4 Underground horizontal cave with flame rising in Luoyang North Kiln, Henan Province.
Fig. 5 Schematic diagram of copper melting furnace envisaged by Barna.
2 explosion
The application and improvement of blast equipment is very important to the development of metallurgical technology.
Clay pipes have been found in all copper casting sites in Anyang (Figure 6). There is no doubt that there is copper slag on the surface of a few mud pipes, which is related to bronze casting. Similar relics have been unearthed at the site of bronze casting in Houma, which is considered as a blowing tool. A similar discovery was made in Joo Won?. In Telekot's book Metallurgical History, there are materials used by Egyptian goldsmiths to blow pipes with pottery nozzles (about 1460B. C, as shown in figure 7). However, the usage of this clay pipe may be different from that of this Egyptian blowpipe, and I'm not sure how to use it.
Fig.6 clay pipe unearthed from the bronze casting site in southeast Xiaomintan.
Fig. 7 Egyptian goldsmiths use pottery blowpipes to blow fire to help melt (quoted from China Ancient Metal Technology, page 326, fig. 8-20).
Although we don't know exactly when it started, this kind of airbag blower is recorded in ancient books. Although there are no remains of Qiang or other blowers in Shang Dynasty, there is the word ""in the appendix 1 1, which generally appears on Jue, Zhang and Ding, and looks like leather, so it should be the ancient Chinese character of "Qiang", which is also found in Oracle Bone Inscriptions's Compilation.
In the Qing dynasty, Liu? 1? According to Yunqi's Mining Administration, this leather bag is made of a whole piece of black goat skin, leaving only a small hole in the abdomen and stuffing it into a bamboo tube, which is about two or three inches deep. When in use, put the leather bag on your feet and step on it with your feet. Hold the skin in one hand and press it from top to bottom, and the wind will be sprayed out of the bamboo tube, which can be used for cooking and smelting. The original form of this kind of leather wind bag is still used by many primitive nationalities, such as Tibetan leather bag (Figure 8) seen in ethnological investigation, which consists of ventilation pipe, leather bag and sealing device, and the operator controls the blowing by hand. India also has similar materials, which are very similar to those used by Tibetans (Figure 9). This tool is very suitable for small-scale smelting, light and convenient to make.
Figure 8 Tibetan skin (quoted from the master's thesis of Wang Gong)
Figure 9 Airbags used in India
At present, it is impossible to know the instruments and action forms of air blowing in Anyang period, but according to records, air blowing was used many times as early as the Warring States period. Judging from the temperature and scale of alloy smelting in Anyang at that time, it is likely that many blowers have been used, and the blowers in Shang Dynasty may be more complicated than the leather used by Tibetans.
Preparation of 3 alloy
The preparation of bronze alloy in Shang dynasty was carried out in a special casting site or workshop. By the late Shang Dynasty, he had mastered the smelting technology of Cu-Sn-Pb ternary alloy. At that time, craftsmen had a deep understanding of the relationship between bronze alloy proportion and mechanical properties, and had strict control over the operation, so they could deliberately use different proportions of alloys according to different uses. At the same time, whether the supply of raw materials is sufficient, the change of social atmosphere and the level of status may all affect the alloy proportion of bronzes.
However, so far, the technical problems of alloy preparation of bronze wares in Yin ruins have not been solved. A rectangular copper block was unearthed in the copper casting site in the north of the nursery, and some scholars concluded that it was used as a spare material for casting bronzes. Is this copper block a low tin alloy ingot deliberately produced by people? Or the agglomeration of excess molten metal when casting tin bronze? Is the tin in this copper block artificially and consciously added, or is it brought in when smelting tin-bearing copper ore? Still to be decided. Since no tin ingots were found, how a large number of tin bronzes unearthed in Yin Ruins were alloyed needs further study. Two lead ingots were unearthed from pit E 16 in Xiaotun Village, Yin Ruins. The metal parts of the two lead ingots contain high purity lead and trace amounts of zinc and arsenic. The existence of lead ingot shows that bronze alloy is directly prepared from metal lead. . In recent years, a large oval metal block was found in a well of Shang Dynasty in Laiyang. It will be helpful for analysis and detection.
(3) pouring
Pouring is the process of injecting molten copper alloy into the mold cavity. In order to improve the filling ability, measures such as preheating the mold, overheating pouring and preparing alloys with strong filling ability can be taken.
Preheating the mold is one of the measures to improve the filling ability. When the Shang bronzes were restored, Wan Jiabao preheated the mold to 300-400℃, Feng Fugen and others preheated the mold to 400-500℃, and the mold temperature was 200-300℃ when pouring, all of which achieved satisfactory results.
Whether it is pure copper or copper alloy, the higher the liquid temperature, the better the fluidity and the stronger the filling ability, and vice versa. Therefore, the pouring temperature is higher than the melting point. Modern casting technology calls this temperature difference overheating temperature. The pouring temperature of cast copper in Yin and Shang dynasties has not been reported so far. During trial casting, the melting temperature of Wan Jiabao is 1350℃, the melting temperature of Feng Fugen and others is 1200℃, and the pouring temperature is1100 ~1200℃. According to the furnace temperature of Luoyang Beiyao Western Zhou copper casting site is 1200 ~ 1250℃, it shows that the trial casting of Feng Fugen and others is closer to the real situation. In addition, the higher the overheating temperature, the greater the gettering ability of copper alloy, which is easy to cause porosity in castings. So the control of overheating temperature should be just right.
Small vessels should be cast by ladle, and large bronzes may be cast by ladle and channel. A semi-crypt shed with a rectangular soleplate at the bottom was unearthed at the copper casting site in Beidi, Nursery, as shown in the previous figure 16. At the same time, several gray and shiny flow surfaces with flow direction are retained, which are presumed to be the channels for copper liquid to flow. From these phenomena, it can be guessed that if the ladle was put on the ground and poked open during casting, the copper liquid could be injected into the mold at the bottom of the shed from the channel. The bottom mold of a large round object unearthed from Xiaomintun bronze casting site is also located in F43 of the semi-tomb, which shows that this speculation is reasonable. When casting large objects, it is possible that the groove injection method included in Wu Kaizhong of Tiangong has been adopted, and 4 to 8 pouring ladles are used for groove injection at the same time.
(4) Post-pouring treatment
Xunzi? 6? 1 the national seal of Xinjiang says that "the punishment of punishment is right, gold, industrial refining, fire refining and car cracking." However, you can't break the rope without peeling and sharpening. Peel it off and grind it, then lick the plate, lick the cattle and horses, and immediately hear it. " This passage not only refers to bronze sword casting, but also has universal significance in the production of bronze wares in the pre-Qin period. He cast the device into two stages: casting and post-casting treatment.
Among them, the first four sentences summarize the four elements of the ancient bronze smelting and casting process, that is, the mold must be correct in shape and size, the alloy should be made of high-quality copper and tin, the craftsman should have skilled skills, and the alloy should be melted and poured properly. This reflects people's understanding of the key points of smelting and casting technology in the pre-Qin period and is often quoted by people. However, the proportion mentioned in the latter paragraph is much lower than the former, which shows that people do not put post-casting treatment in its proper important position. In fact, post-casting treatment plays a key role in the final quality of devices, which usually includes stripping, cleaning and polishing. Castings with local defects after demoulding need to be repaired.
After the object is cast and cooled, it can be taken out by tapping hard. Because the mud core is attached to the device, it is difficult to take it out, so it needs to be chiseled out with tools. Then use a hammer, saw, chisel and scraper to remove the gate, flash, burr and meat. The tools used include some metal tools, such as bronze carving and bronze carving needles.
There are two ways to repair the bronzes in Yin Ruins. One is the so-called melting repair, that is, the molten copper is poured directly on the holes or cracks that need to be repaired; The other is casting, if it is a part or accessory of bronze ware, such as foot or? 1? 7 and so on. For various reasons, it is either cast or broken, so we should make a model on the residual material and then pour it on and weld it with the car body.
Billets become finished products with good appearance, and tempering plays an important role. The wear marks on many bronze ritual vessels are still clearly discernible, and they should be made of thick stones and thin stones. Thousands of grindstones of different sizes, thicknesses and shapes have been unearthed from Xiaomintun copper casting site. There are two kinds of materials, coarse sandstone and fine sandstone, to polish and trim the bronze surface, which also shows the great workload of this process. Charcoal from bronze casting sites in Yin Ruins often comes out with stones. After polishing, you can use charcoal to polish the utensils in water to make the bronzes shine.
Then, in the casting process, what is the workload of late casting processing? Due to the lack of records, it is difficult to confirm only the unearthed objects and smelting and casting remains. Hua Jueming made a statistical calculation according to the records in Volume 95 of the Rules of the Ministry of Industry, edited by Shi Yizhi and Decheng in the 24th year of Qianlong, and made a conclusion. 1? For the 7-level ritual vessels, the labor consumption in the casting stage only accounts for 4.20% ~ 5.30% of the total labor consumption. If the amount of casting labor is 1, the amount of labor prepared in the early stage is 7.07 ~ 8.92, and the amount of labor processing after casting is as high as 10.29 ~ 15.09. Even if the techniques of internal rotation, engraving and ancient bronze ware firing are excluded, it is still as high as 6.29 ~ 10. 18. It can be inferred that the bronze ritual vessels of Shang Dynasty are complex in shape, and only bronze vessels and stone tools are used for operation. According to the complexity of the vessels, they are close to the category of 6 ~ 10, such as Simuwu Ding and Simuwu Ding Xin, or more are needed.
Perhaps it is precisely because the later casting process is so complicated that the foundry is forced to find ways to improve the process from generation to generation. It may be related to the developed casting technology of bronze ritual vessels in Yin Ruins and the strict casting technology of copper. Under certain conditions, the pressure of unfavorable factors is an important driving force to promote process replacement. Understanding this will help us understand the essence of technological evolution and the dialectical relationship between related factors.