... varying proportions in porcelain, china and earthenware. Earthenware contains on an average12% feldspar 25% ball clay 28% china-clay 35% quartz ... soda and potash feldspars and also contains lime which is an important ingredient of glass, is not preferred in the glass ... containing below 0.4% Fe2O3 is preferred. Feldspar is also an important constituent for the preparation of white and coloured enamels ...