The Sichuan Basin provides lots of bronzes from the late Zhou period with special patches. Four bronze weapons in the Chengdu Museum were studied by scanning electron microscopy and metallography. The metallographic analyses of 2 cross-section samples indicated a cast structure. The mean percentage of tin is 11%. Experimental work showed that the patch regions mainly made up of tin and copper have oxidation resistance. There are two methods to produce the patch on the surface of the three bronze weapons. One method is to cast metal out of flatness, then plating paste of high tin alloy on the bulge of the metal. The second method is to cast leveling metal, then plating paste or tin coating on the site where silver patch should appear. -- ICCROM