Bismuth nanoclusters embedded in germanate glass matrices and surface layer of bismuth grains have been obtained by thermal treatment in hydrogen atmosphere of Bi_0.33Ge_0.67O_1.84 and Bi_0.57Si_0.43O_1.72 glass. The composite Bi-glasses were investigated by differential scanning calorimetry, X-ray diffraction and atomic force microscopy methods. A depression of the melting point of Bi from 544 to 387 K was found for nanosized bismuth particles embedded in glass and to 502 K when these are on the surface. It is shown that melting and solidification of bismuth nanocrystals induce a large change in surface conductivity of reduced glasses. A simple two-layer model of reduced glasses explains the evolution of surface layer and electrical properties of the materials during the reduction process.