The northernLanna Kingdom , which lasted from 1239 to 1564, used leaf (or line) money made of brass and silver bubbles, which is called "pig-mouth" money . Nobody has been able to duplicate the technique of making pig-mouth money, and because the silver is very thin and breakable, good pieces are now very rare.Flower money , which is flat, round and small, is of better quality silver than other coins from this period. One side is decorated with flower like patterns, and the reverse face is dented or pitted. Bracelet money was also used in the Lanna Kingdom. Called this because of their shape, bracelet coins are actually too small to fit around a wrist, although some experts believe that this type of coinage originated in a larger size that was worn by mountain people around the wrist for easy transport. King Ramkhamhaeng (1279-1298) of Sukhothai is credited with introducing bullet coins. Some experts think they were developed to resemble cowry shells, which had been used as money from ancient times. Others believe they were only a more convenient form of bracelet money.