Monitoring deflocculated particles in a suspension

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, the method comprising applying such a field to such a region of a first sample of suspension whose degree of deflocculatin is desired to be monitored and applying such a field to such a region of a second sample of suspension, whose particles are known to be substantially fully deflocculated, detecting the change in radiation scattering properties of each region due to the field to produce a respective output indication, and comparing the indications to produce an indication related to the degree of deflocculation of the particles in the first suspension.