Disclosed is a process of preparing a moulded article, comprising 1) hydrolysing a) at least one silane having one non-hydrolysable organic group, and b) at least one compound selected from b1) a silane having two non-hydrolysable organic groups, and b2) a hydrolysable polysiloxane, or a mixture thereof, and c) optionally at least one silane having no non-hydrolysable organic group, to prepare a composite composition comprising a hydrolysate or condensate, 2) placing the composite composition in a mould, 3) curing the composite composition to increase the degree of condensation, 4) removing the moulded article from the mould, and 5) heat treating the moulded article at a temperature of at least 100°C. The moulded article is preferably an optical lens which may be used for automobile headlights.