China has a long and brilliant history of metallurgy and casting. Its splendid casting techniques ushered in the resplendent Bronze Age. Perfect workmanship brought about exquisite pieces of art.
An accurate mixture of metals for alloy, a division of work between the extracting furnace and the smelting furnace, the replacement of the pottery base furnace by the clay furnace, the appearance of the sand furnace and the furnace of comprehensive materials, the evolution of the air blower from the air bag to the bellows, the use of the metal mould method and the lost-wax method, the ingenious application of the way of combined moulds and separate casting and the way of separate moulds and combined casting and the development from the casting of a single surface shaping furnace to the casting of pit shaping furnaces embodied the great wisdom of the Chinese nation and the scientific and technological progress in ancient times. Summing up their experiences gained over a long period of time, our ancestors acquired a good grasp of metal smelting and casting techniques. The book Xun Zi summarizes the essentials of bronze casting technology as follows: "Correct moulds, fine mixture of copper and tin, ingenious workmanship and consummate smelting."
The three-dimensional models, simulated operating demonstration and operation by visitors at the exhibition room demonstrate the process of casting bells in ancient times.
The day mould method and the lost-wax method were the main methods used to cast bells in ancient China.
I. The clay mould method included the procedures of making outer moulds, making inner moulds, drying the moulds, combining the moulds, smelting and casting.
Outer moulds could be made on models or with a scraper. Inner moulds could he made with a scraper or a molding set. The drying process was designed to make the moisture content in the mould evaporate thoroughly so as to increase the strength of the mould.
Crucibles and air bags were the main smelting equipment in the early days. Large smelting furnaces and bellows were used during the Ming and Qing dynasties.
II. The lost-wax method included the procedures of making inner moulds, applying wax and carving, making outer moulds, melting wax and drying the moulds, smelting and casting.
1. Build an inner bell mould with clay; 2. Coat the inner mould with butter mixed with wax; 3. Carve the solidified wax into the desired shape of the bell; 4. Coat the wax with clay and leave an outlet for the wax; 5. Heat and melt the wax to make the wax flow out of the outlet, form a cavity, and continue the heating to dry the bell mould thoroughly; and 6. Melt metal and do casting.
An ancient bell was cast through those procedures.