Abstract: For forming by pyrolysis a coating based upon silicon, oxygen and carbon, on the surface of a moving glass substrates from a percursor gaseous mixture essentially without any oxidizing component and comprising a silane and an ethylenic compound, the contact time between this precursor mixture and the glass is maintained at a value greater than that necessary for the deposition of the coating if this were performed from a precursor gaseous mixture containing an oxidizing agent. The coating thus obtained has a refractive index lying between 1.45 and 2, preferably between 1.6 and 1.9, and its thickness reaches values greater than 50 mm.