As part of a larger body of work aimed at developing mathematical models of the wet drum magnetic separator in dense medium separation, four factorial experiments, each of sixteen trials, were carried out using magnetite feed to such a separator. This work was done in a purpose built rig based on a small industrial scale (700mm lip length, 900mm diameter) wet drum magnetic separator. The magnetite lost in these trials, that is reporting to the effluent, was universally found to be of lower susceptibility than the feed, but was commonly found to be coarser than the feed. These observations are explained in terms of a conceptual model of the mechanism by which magnetic material is captured. This explanation is supported by both magnetic theory and high speed photography. It is proposed that the capture of magnetic particles in the wet drum magnetic separator is by a flocculation process which proceeds rapidly at high pulp density, but only very slowly with low pulp density feeds. (C) 2000