Tin allowed for the much more complex shapes cast in closed moulds of the Bronze Age. Arsenical bronze objects appear first in the Near East where arsenic is commonly found in association with copper ore, but the health risks were quickly realized and the quest for sources of the much less hazardous tin ores began early in the Bronze Age. This created the demand for rare tin metal and formed a trade network that linked the distant sources of tin to the markets of Bronze Age cultures. Cassiterite (SnO), the tin oxide form of tin, was most likely the original source
Tin(II) chloride to maintain the equilibrium towards the left-hand side (using Le Chatelier's principle). Solutions of SnCl are also unstable towards oxidation by the air: This can be prevented by storing the solution over lumps of tin metal. There are many such cases where tin(II) chloride acts as a reducing agent, reducing silver and gold salts to the metal, and iron(III) salts to iron(II), for example: It also reduces copper(II) to copper(I). Solutions of tin(II) chloride can also serve simply as a source of Sn ions, which can form other tin(II) compounds via precipitation reactions. For example, reaction with sodium sulfide produces