 By the mid 10th century, the mintage of copper coins began to phase out and the use of commodity money such as rice, silk, and clothes which all maintained stable value were used in place of the coins.Commodity money began to gain economic value and status and became the stable criteria for evaluating monetary value of various goods and services.Since carrying rice, silk, and clothes was cumbersome and inconvenient, a credit economy emerged to burden the shoulder of transportation and handling costs.