The experimental performance of a high gradient magnetic separator has been previously reported by other workers in some detail for a CuO/Al2O3slurry. Less detailed results were also reported for slurries of Mn2O3, Al, and α-Fe2O3particles with Al2O3representing a 20:1 range in particle sizes and a 200:1 range in magnetic susceptibility. Examination of these results indicates that many layers of particles build up on each filter fiber. Accordingly, in this paper we extend the original particle trajectory model for the calculation of filter performance, to include the build-up of multiple layers of particles on the fibers. Good agreement is obtained between the calculated recoveries and purities for all of the particles and the experimentally reported values using a filter packing efficiency and a mechanical trapping term, derived from the CuO data, as adjustable parameters.