A method of producing a glass body composed of two or more oxides by the flame hydrolysis technique, for example incorporating an additive or dopant oxide in a fused silica glass body. The method comprises forming a gas stream containing vapors of a compound that will hydrolyze to a glass forming oxide, e.g. silicon tetrachloride (SiCl4), entraining an oxide, or material convertible thereto, in the form of solid particles not over about one micron in size, and simultaneously passing the vapors and particles into a flame of combustible gas to form and codeposit an oxide mixture.