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2023.1.28
There are two basic methods for the casting of ancient Chinese bronzes: block molding method and wax loss method. In addition, there are separate casting method and welding method. Now, let’s find out how ancient bronzes were forged.
The block pattern method, or soil pattern method, was first adopted by the ancestors of the Shang and Zhou dynasties, and was the most widely used bronze casting method in the whole bronze age. The method steps are as follows
Mold making
A module is also called a parent module or a model. The raw materials can be pottery, wood, bamboo, bone, stone and other materials, and the cast bronze can also be used as models. The specific material to be selected depends on the geometric shape of the casting, and the convenience of pattern carving and molding shall be considered. Generally speaking, thin, long and flat knives and cutting moulds can be made of bamboo and wood; Smaller animals and birds can be carved into molds with bones and stones; For the heavy and relatively large Ding and Yi vessels, clay can be used as the mold for the purpose of molding.
Model
Proper clay materials shall be selected and prepared for molding, and its main components are soil and sand. Apply mud on the outside of the mold to remove the mold components used to form the casting outline, which is called the outer mold in the casting process. The outer mold should be divided into several pieces to remove from the mold; In addition to the outer model, a model with a volume equivalent to the inner cavity of the container should be made of clay, which is usually called core, or heart-shaped and inner model; Then the inner and outer moulds are sleeved together. The gap in the middle is called the cavity, and its spacing distance is the thickness of the cast objects. Generally speaking, the clay (preferably clay) used for exterior molding has a larger content, while the clay used for core has a larger content of sand and coarser particles. Fan’s clay is very carefully prepared. The collected soil shall be dried, broken, sieved, mixed, and added with a certain proportion of water to form a moderately soft and hard soil. Then it shall be repeatedly beaten and rubbed, and then soaked for a long time to make it qualitative. Only in this way can the prepared clay be handy when turning the model.
Turning over the mold block from the mold is the central link of mold casting technology, which requires a high skill. For simple solid objects such as knives, daggers, arrowheads, etc., Erhefan can handle it easily, that is, only two outer models need to be made from the model. Compared with the simple manufacture of the above utensils, the model for manufacturing hollow containers is much more complicated. Before turning over the model, we must first clarify the number and distribution of external models. Here is a brief introduction to its preparation: the first step is to make the outer wall. The surface of the mold shall be stacked with clay without gaps, and then pressed tightly to ensure tightness. Next is to make the inner wall. There are three ways to do the inner wall: the first is to scrape the surface of the model after the outer mold is turned over from the model. The model is the inner core, so the thickness of the scraped model is the thickness of the cast copper; The second method is used for large implements, which is to make the model hollow, take its inner core as the model, connect the core and the bottom mold into a piece, and then cast the ear on the bottom mold; The last one is to use the outer mold to make the core.
Pouring
Pour the baked and assembled fan while it is hot, or preheat it before pouring. The preheating temperature should be 400-500 ℃. During preheating, the core shall be assembled in a complete set, tightly bound, and then tightly mixed with sand or grass, and then baked at high temperature in the kiln. In order to prevent the expansion of the mold caused by the pressure of molten copper and the collapse of the mold caused by high temperature, the baked mold needs to be buried in the sand (wet sand) pit and clamped with wooden strips.
After the fan is preheated and ready, pour molten copper (1100 – 1200 ℃ is appropriate) into the gate. The objects should be poured upside down in order to concentrate the impurities in the pores and copper liquid at the bottom of the objects, so that the upper and middle parts of the objects are dense and the patterns are clear. When pouring molten copper, the speed should be controlled, and the speed should be fast and flat until the gate air hole (the air hole left on the mold) is full of molten copper. After the copper liquid is solidified and cooled, the mold and core can be removed and the casting can be taken out.
The method of casting into a complete shape at one time is called “muddy casting”, “muddy casting at one time” or “integral casting”. Most Shang and Zhou artifacts were cast in this way. The lines left on the surface of the objects cast by this method are continuous, that is, each model line is connected with each other.
Finishing
After removing the ceramic mold, the casting should be trimmed by hammering, sawing, chiseling and other processes to eliminate the redundant copper blocks, burrs and flash. Only when a smooth and tidy bronze product appears can it be considered as finished.
The wax loss method is to make the inner mold with beeswax mixed with grease, apply mud on the inner mold, reserve holes, and make the outer mold. After the outer mold is dried, calcined at high temperature, the inner mold melts into liquid, and discharged from the hole. The outer mold forms the same cavity as the inner mold, and then inject copper liquid from the hole. After cooling, peel off the outer mold to obtain the same casting as the inner mold. This is a precision casting method for bronze and other metal objects, which is still used in modern industry. It is known that the earliest artifacts cast by the lost wax method in China are in the late Spring and Autumn Period, which are the bronze ban in the Chu tomb of the Xiasi Temple in Xichuan, Henan Province. The exquisite craftsmanship indicates that it is not the original production. However, Chu made the most contributions to the production of exquisite and wonderful products, and the statue plate of the tomb of Marquis Yi of Zeng was also the most praised. The coil cobra patterns on it were exquisite and exquisite, extremely complicated and magnificent, which was made by the wax loss method. However, the application of the lost wax method is not popular enough, and the number of works seen today is always small, which is related to the limited quantity of beeswax and the complexity of production, and perhaps also due to the fact that although the effect is marvelous, it is difficult to elicit the universal aesthetic pleasure connection.
The history of the lost wax method in China can be traced back to the Spring and Autumn Period and the Warring States Period. The earliest bronze ware cast by the lost wax method is the Xiong Shen Yu of the Communist King of Chu.How ancient bronzes were forged