a method of preparing particles of a substance , for example selected from a flavor , fragrance , pigment , dye , biologically active compound or a plastics material , comprises contacting the substance of a formulation with a first solvent which comprises a c1 - c4 hydrofluorocarbon , especially tetrafluoroethane , and subjecting the resultant mixture to a separation process , for example , by allowing the mixture to be sprayed as a mist from a high pressure environment in a first vessel to a low pressure environment in a second vessel , thereby to cause separation of a least some of the substance from the first solvent and the formation of fine particles of the substance .