The composition and microstructure of Cizhou monochrome overglaze enamels, the first known form of overglazed enamels in China, and green lead glazes from Guantai kiln were determined. Although microstructure and thickness of the enamels were very similar to those found for the single layer lead glazes, lead contents were lower. Enamels from the later part of the twelfth century formed a narrower compositional grouping than the lead glazes, indicating that increased control of the technology of the technology was attained. The monochrome enamels are thicker and have a composition distinct from that published for later painted enamels from sites other than Guantai. Increased viscosity and decreased values of thermal expansion coefficients were calculated for Guantai enamels relative to the glazes. An attempt to promote adhesion and reduce crawling may have caused the use of lower lead in the enamels relative to the single layer lead glazes.