A method for producing a glass-like protective layer on a metal substrate or glass substrate or a pre-coated metal substrate or glass substrate, said method comprising the steps of a) mixing one or more silicon compounds of formula (I) R n SiX 4-n (I) where R is independently alkyl, aryl, alkaryl or arylalkyl, X is independently alkoxy or acyloxy, and n is 0, 1 or 2, with the proviso that at least one silicon compound of formula (I) is used, where n is 1 or 2, with NaOH and KOH, b) adding water to the mixture obtained in step a) to hydrolyse the silicon compound(s) of formula (I), c) adding at least one compound of formula (II) MY m (II) where M is Pb, Ti, Zr, Al or B, preferably Ti, Y is independently alkoxy, and m corresponds to the valence of M, wherein one or more alkoxy groups may be replaced by one or more chelating agents and/or two alkoxy groups may be replaced by an oxo group, to the hydrolysed mixture obtained in step b), wherein the molar ratio M/Si is in the range of 0.01/1 to 0.04/1, wherein M is the molar amount of M in the at least one compound of formula (II) and Si is the molar amount of Si in the at least one silicon compound of formula (I), to obtain a coating sol, d) applying the coating sol obtained in step c) to the metal substrate or glass substrate or the pre-coated metal substrate or glass substrate, and e) thermally compressing the coating sol applied in step d) at a temperature in the range of 300°C to 500°C to form the glass-like protective layer. a) mixing one or more silicon compounds of formula (I) R n SiX 4-n (I) where R is independently alkyl, aryl, alkaryl or arylalkyl, X is independently alkoxy or acyloxy, and n is 0, 1 or 2, with the proviso that at least one silicon compound of formula (I) is used, where n is 1 or 2, with NaOH and KOH, where R is independently alkyl, aryl, alkaryl or arylalkyl, X is independently alkoxy or acyloxy, and n is 0, 1 or 2, with the proviso that at least one silicon compound of formula (I) is used, where n is 1 or 2, with NaOH and KOH, b) adding water to the mixture obtained in step a) to hydrolyse the silicon compound(s) of formula (I), c) adding at least one compound of formula (II) MY m (II) where M is Pb, Ti, Zr, Al or B, preferably Ti, Y is independently alkoxy, and m corresponds to the valence of M, wherein one or more alkoxy groups may be replaced by one or more chelating agents and/or two alkoxy groups may be replaced by an oxo group, to the hydrolysed mixture obtained in step b), wherein the molar ratio M/Si is in the range of 0.01/1 to 0.04/1, wherein M is the molar amount of M in the at least one compound of formula (II) and Si is the molar amount of Si in the at least one silicon compound of formula (I), to obtain a coating sol, where M is Pb, Ti, Zr, Al or B, preferably Ti, Y is independently alkoxy, and m corresponds to the valence of M, wherein one or more alkoxy groups may be replaced by one or more chelating agents and/or two alkoxy groups may be replaced by an oxo group, to the hydrolysed mixture obtained in step b), wherein the molar ratio M/Si is in the range of 0.01/1 to 0.04/1, wherein M is the molar amount of M in the at least one compound of formula (II) and Si is the molar amount of Si in the at least one silicon compound of formula (I), to obtain a coating sol, d) applying the coating sol obtained in step c) to the metal substrate or glass substrate or the pre-coated metal substrate or glass substrate, and e) thermally compressing the coating sol applied in step d) at a temperature in the range of 300°C to 500°C to form the glass-like protective layer. <EOS>