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.