Abstract: A method of monitoring the deflocculation of particles in a suspension, which particles, when deflocculated, are such that they can become aligned in an applied field, comprises applying a beam of radiation to a region of the suspension, applying a field to the region and detecting a change, if any, in radiation scattering properties of said region due to the aligning of deflocculated particles, if any, of the suspension in the field, wherein said suspension is passed through a cell which is transparent to said radiation and provides said region in which said field is produced and on to which region said radiation is applied and wherein said suspension is pumped through said cell and the field is applied in bursts timed with the pumping operation.