Abstract: Three samples with mottle (Hu-ban-wen) were analyzed by using SEM, XRD and microscope. The matrix of these samples was cast and then heated. Distinct interface between the matrix and mottle existed. The mottle layer was high tin bronze and the thickness was about 20-40μm. SnO₂ and Cu₄₁Sn₁₁ were main composition of the mottle layer. Some experiments were carried out by using the methods of coating with Cu-Sn alloy solution and hot-tinning. Clear boundary and columnar crystal growing could be seen clearly by all these methods and varied thickness of the coating was caused by different heating conditions. The result shows that the mottle is artificial, the columnar crystal growing from substrate to coating should be caused by dissolving and diffusion of copper into liquid tin and δ phase maybe caused by hot-tinning and annealing.