Abstract: A method for the manufacture of foamed ceramics from a starting composition containing at least one component, which, when heated, forms a viscous, sintered and porous mass and a relatively difficultly oxidizable pore-forming agent for producing the porous structure, characterized by using as the starting composition a composition containing (1) at least one waste product rich in silica and containing readily oxidizable substances which, when heated, are themselves capable of producing uncontrollable pore formation and/or an undesirable melt, and (2) a strongly oxidizing agent, the quantity of oxidizing agent being such that the oxidizable substances are oxidized to eliminate or to reduce the uncontrollable pore formation and/or the melting and wherein the desired pore structure is obtained by oxidation of the difficultly oxidizable carbonaceous pore-forming agent.