Abstract: Finely divided glass, which may have a viscosity between 10.sup.6 and 10.sup.7 poises at 950.degree.C to 1100.degree.C and which may be of a composition suitable to conversion into a vitroceramic, is mixed with up to a few percent by weight of a foaming agent including a mixture of SnO.sub.2 and SiC, in equimolar proportions or with an excess of SiC. The resulting mixture is heated to 950.degree.C to 1100.degree.C to effect foaming by evolution of CO.sub.2 from the foaming agent, and the resulting glass foam is cooled. The nucleation and crystallization steps by which the glass is converted to a vitroceramic may be caused to occur without allowing the foam to return to room temperature.