amide, methacrylamide, methyl acrylate, ethyl acrylate, n-butyl acrylate or with methyl methacrylate.Examples of anionic protective colloids are homo- and copolymers of monoethylenically unsaturated carboxylic acids and salts thereof, in particular sodium and ammonium salts thereof, e.g. homo- and copolymers of acrylic acid, of methacrylic acid or of maleic acid, optionally with neutral comonomers