Processes and compositions for printing substrates. A printing paste containing a matrix-forming precondensate containing polyorganosiloxanes obtained by a sol-gel process and at least one coloring, luminescent, conductive and/or catalytically active filler is applied imagewise to the substrate and is densified by heat treatment at a temperature below the glass transition temperature of the matrix being formed. The processes and printing pastes are suitable, for example, for the production of conductor tracks and decorative patterns.