According to a first aspect of the present invention there is provided a process for preparing a particulate solid comprising the steps i) to iv): i) providing a dispersion of polymer particles in a liquid medium, said polymer being obtained or obtainable by the copolymerization of at least the monomers in components a) to d): a) 45 to 90 parts of one of more hydrocarbyl (meth) acrylates each having a homopolymer Tg of from 90 to 130° C. and having no hydrophilic groups; b) 10 to 55 parts of one or more ethylenically unsaturated monomers each having homopolymer Tg of below 90° C. and having no hydrophilic groups; c) 0 to 40 parts of one or more styrenic monomers having a homopolymer Tg of at least 90° C. and having no hydrophilic groups; d) 0 to 10 parts of one or more ethylenically unsaturated monomers each having at least one hydrophilic group; wherein all the parts are by weight; ii) associating the particles to form clusters of particles; iii) optionally stabilizing the clusters; iv) heating the clusters above the glass transition of the polymer.