A composite material having less than about 25 volume percent refractory particles in a metal matrix is concentrated to have about 37-45 volume percent refractory particles. The concentrating is preferably accomplished by heating the composite material to melt the matrix, and then contacting the molten composite material to a porous element having an average pore size greater than that of the average particle size. A small pressure differential, on the order of about one atmosphere, is applied across the porous element, so that metal matrix material separates from the composite material and flows through the porous element. The particulate volume fraction in the composite material gradually increases. When the particulate volume fraction exceeds about 37 volume percent, the mass of composite material becomes semi-solid and freestanding. The resulting composite material may be further processed, as by forming to a useful shape or diluting with another matrix material.