Calcium carbonate, in particular natural calcium carbonate, or dolomite is in the form of a 65-75% slurry and the hydrosilicate, e.g. talc, is likewise in the form of a 65-75% slurry (dispersed with the previously mentioned polyacrylates and wetting agents known per se) and the two pigments are then mixed together by means of mixers and dispersing units and brought to a solid content of about 75%