A method for producing a substrate precursor having a mass of more than 50 kg, comprising a TiO2-SiO2 mixed glass, comprising the steps of: • introducing a silicon dioxide raw material and a titanium dioxide raw material into a flame, • producing a glass body having a titanium dioxide content of 3 wt.% up to 10 wt.%, the glass body comprising: • a macroscopic, production-related titanium profile (410, 410', 410", 410′′′), and • a microscopic, production-related layer structure, • dividing the glass body into a plurality of rod-like glass body portions (400, 400', 400", 400′′′), • spatially measuring the titanium profile (410, 410', 410", 410′′′) in each of the glass body portions (400, 400', 400", 400′′′), • connecting the glass body portions (400, 400', 400", 400′′′) to form an elongate first glass component, • first homogenization treatment of the first glass component, • pushing together the first glass component in order to produce a spherical glass system, • turning the glass system by more than 70 degrees, • pulling apart the glass system to form an elongate second glass component, • second homogenization treatment of the second glass component in order to produce a substrate precursor, the substrate precursor being substantially layer-structure-free, characterized in that the step of measuring comprises the following steps: • predetermining a desired spatial titanium distribution in the substrate precursor, • providing a model of a titanium partition in the substrate precursor, the model being dependent on • an arrangement of the plurality of glass body portions (400, 400', 400", 400′′′) in the first glass component relative to one another, • the spatial titanium profile (410, 410', 410", 410′′′) in each of the glass body portions (400, 400', 400", 400′′′), and • the effects of the step of pushing together and the step of turning on the spatial titanium profiles (410, 410', 410", 410′′′) in the glass body portions, • calculating an optimal arrangement of the glass body portions (400, 400', 400", 400′′′) relative to one another using the model, so that a difference between the titanium partition and the titanium distribution is minimal, • positioning the glass body portions (400, 400', 400", 400′′′) so that in the step of connecting the glass body portions (400, 400', 400", 400′′′) are connected according to the calculated optimal arrangement. • introducing a silicon dioxide raw material and a titanium dioxide raw material into a flame, • producing a glass body having a titanium dioxide content of 3 wt.% up to 10 wt.%, the glass body comprising: • a macroscopic, production-related titanium profile (410, 410', 410", 410′′′), and • a microscopic, production-related layer structure, • a macroscopic, production-related titanium profile (410, 410', 410", 410′′′), and • a microscopic, production-related layer structure, • dividing the glass body into a plurality of rod-like glass body portions (400, 400', 400", 400′′′), • spatially measuring the titanium profile (410, 410', 410", 410′′′) in each of the glass body portions (400, 400', 400", 400′′′), • connecting the glass body portions (400, 400', 400", 400′′′) to form an elongate first glass component, • first homogenization treatment of the first glass component, • pushing together the first glass component in order to produce a spherical glass system, • turning the glass system by more than 70 degrees, • pulling apart the glass system to form an elongate second glass component, • second homogenization treatment of the second glass component in order to produce a substrate precursor, the substrate precursor being substantially layer-structure-free, • predetermining a desired spatial titanium distribution in the substrate precursor, • providing a model of a titanium partition in the substrate precursor, the model being dependent on • an arrangement of the plurality of glass body portions (400, 400', 400", 400′′′) in the first glass component relative to one another, • the spatial titanium profile (410, 410', 410", 410′′′) in each of the glass body portions (400, 400', 400", 400′′′), and • the effects of the step of pushing together and the step of turning on the spatial titanium profiles (410, 410', 410", 410′′′) in the glass body portions, • an arrangement of the plurality of glass body portions (400, 400', 400", 400′′′) in the first glass component relative to one another, • the spatial titanium profile (410, 410', 410", 410′′′) in each of the glass body portions (400, 400', 400", 400′′′), and • the effects of the step of pushing together and the step of turning on the spatial titanium profiles (410, 410', 410", 410′′′) in the glass body portions, • calculating an optimal arrangement of the glass body portions (400, 400', 400", 400′′′) relative to one another using the model, so that a difference between the titanium partition and the titanium distribution is minimal, • positioning the glass body portions (400, 400', 400", 400′′′) so that in the step of connecting the glass body portions (400, 400', 400", 400′′′) are connected according to the calculated optimal arrangement.