The ceramic piece-mould casting technique was predominant in the Chinese Bronze Age. A coating layer, often found on the moulds’, models’ or cores’ surface, had important effects on the cast quality. The materials, production and function of the coatings in the bronze casting process have not been sufficiently studied. In this paper, 23 pieces of model/mould/core fragments from the Houma foundry (of the Eastern Zhou period, 770–221 BCE), the largest Bronze Age foundry site found to date in China, were studied using complementary analytical techniques. The results showed different coatings between moulds and models (or cores). Insect wax or animal fat were probably applied to cores. Most of the Houma moulds appeared to have been used in casting. They had been dusted with bone ash, gypsum, calcite or a mixture of these on the fine silty clay surface of the moulds prior to casing to ease the removal of cast artefact from the moulds and obtain a smooth surface on the artefact. Four pieces of moulds from the Yinxu foundry at Anyang, Henan were also studied for comparison.