The invention relates to a water-insoluble silicate glass powder, wherein the silicate glass powder exhibits glass particles with the following composition in percentage by weight on an oxide basis: TABLE-US-00001 SiO.sub.2 20-80 Na.sub.2O 5-30 K.sub.2O 0-5 P.sub.2O.sub.5 0-15 B.sub.2O.sub.3 0-10 CaO 4-30 MgO 0-8 Al.sub.2O.sub.3 0-7 Fe.sub.2O.sub.3 0-2 as well as conventional fining agents in conventional quantities. The invention is characterized in that the glass particles contain at least one of the following components ZnO AgO CuO CeO.sub.2 GeO.sub.2 TeO.sub.2 wherein these components are concentrated in the regions of the glass particles that are near the surface.