This week's Featured Web Site is Sycee On-Line, "Explorer to The World of Ancient China's Silver Treasure". It was suggested by Tom Kays. Thanks!
After a thousand years of circulation, it would seem to be a natural evolution for the shape, weight, and quality of a currency to become streamlined, simplified, and unified. The Chinese silver ingot currency's development, however, was in the opposite direction. It began with the Tang Dynasty's 50 tael rectangular bar and the Sung's axed ends and waisted ingots in 50 taels, 25 taels and 12.5 taels, then proceeded to the Yuan's ingots with their own characteristic shape.
During the Ming, the rims at the ends began to stand up and appear as ears or wings to create the form a preliminary Boat. Later in the Ching Dynasty, in addition to the traditional Boat shape, more distinct varieties of sycee were created, such as Drum, Groove, Square, Trough, Waist, Round, and Saddle; even the Boat shape underwent further evolution as can be seen with varieties like Big-winged and Tortoise.
Each time a silver pattern changed, it became more complicated and more difficult to handle. The casting process of each new silver pattern always required more skill and workmanship, and the entire silver currency system needed more people involved in weighing and assaying. While it kept many people employed, the system also made using silver more and more inconvenient and expensive. Gradually, Chinese silver ingots were replaced by foreign silver coins, and from 1890, Chinese machine struck silver coins began to circulate.
Eventually, China demonetized all silver taels in 1933. Most of the silver ingots in China then were melted down for coining silver dollars.