The project wass designed to test the hypothesis that Chinese overglaze enamels of the 13th to 15th centuries displayed a continuity in composition and a transformation of previous ceramic technology that occurred first in production at northern Cizhou folk kilns and then in the imperial kilns of Jingdezhen in southern China. Previously, the extreme rarity, delicacy and high value of 15th century museum pieces had precluded their analysis. The safe, non-destructive method of PIXE analysis, the expertise of the Research Laboratory of the Museums of France, and permission from two of the premier museums containing Chinese ceramics, created a unique opportunity to fill in a missing link in the story of the development of Chinese overglaze ceramic decoration. The results are explained in terms of the K2O-PbO-SiO2 phase diagram in which are plotted the region of compositional stability and the families of overglaze enamel compositions. The roles of Fe2O3, Al2O3 and CaO in the production of jewel-like overglaze enamel colors on glazed porcelain are explacated. Analysis of the glazes and overglaze enamels on six vessels is set into the framework of analysis of other Chinese lead-containing glazes and overglaze enamels.