In order to provide on a metal substrate a coating having a degree of hardness up to 7 and even higher according to MOHS or DIN 51 150, class A-AA with the same energy as the conventional porcelain-enamel- and glaze method the following components in percentages by weight from 10% to 70% Al2O3 Aluminium oxide from 10% to 30% SiO2 Silicon oxide up to 5% V2O5 Vanadium pentoxide up to 5% P2O5 Phosphorus pentoxide up to 12% R2O Alkali metal oxide up to 20% ZrO2 Zirconium oxide up to 20% TiO2 Titanium oxide are sintered together at temperatures between 800 DEG C and 1000 DEG C, cooled- down,the glassy solidified mass is milled to desired fineness, blended with porcelain enamel or glaze frits up to 50% by weight, proper mill additions being added, the substrate is dipped or flowed in the slip or slip is sprayed thereon, this coating is then fired at a temperature, depending on the substrate material, between 550 DEG and 1200 DEG C.
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