Economical filler or coating pigments for use in increasing the opacity of paper, for example, newsprint or self-copying paper, which have a particle size of 0.1 to 1 mu m, (preferably 0.2 to 0.6 mu m), are made up of aggregates of microcrystals of CaF2 and/or MgF2, bound together by a gelled silica polymer. The pigments may be made by mixing CaF2 and or MgF2 to form an aqueous slurry, or the CaF2, MgF2 and SiO2 may be formed in situ by mixing H2SiF6 and a carbonate and or hydroxide and/or oxide of Ca and/or Mg to form a gelling silica polymer and microcrystals of CaF2 and/or MgF2. In both cases, the microcrystals are thereupon bound into the required pigment aggregates by the polymer.
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