Ke Jun, an academician of the Chinese Academy of Sciences, maintains that the cooling technique of the Yongle Bell was not less difficult and important than other aspects of the casting technology. Bronze alloy is most liable to "hot crack" in the process of cooling which is most harmful to the cast. The big Russian bronze bell with a weight of 193 tons became a dumb bell because cracks appeared in the process of cooling. If the cast cools too quickly, too slowly or unevenly, undesirable consequences may follow. The Yongle Bell was cast with the method of pit shaping. It cooled in the pit like a natural computerized cooling system. It was quite possible that some materials good for the reduction of cooling shrinkage were inserted into the inner mould of the Yongle Bell so as to prevent the body of the bell from being cracked by the inner mould in the process of cooling.
