The introduction of derivative methods and the classification of three flow states (i.e. initial transient, steady and terminal transient stages) provide new approaches to understand the filtration behaviors of liquid aluminum alloys during the Prefil Footprinter tests. The effectiveness of the filtration equations of incompressible cake mode can be well identified over some steady stages during the course of the filtration tests. Based on these new findings a new indirect method of measuring the contents of solid inclusions in liquid aluminum alloys is developed using the Prefil Footprinter tests. However, the benchmarks of specific cake resistance should be made for commercial aluminum alloy melts before this method becomes feasible in laboratories and industries. It is found that for a given volume concentration of solid inclusions, lighter inclusions usually lead to higher specific cake resistance, and the heavier solid inclusions reduce the specific cake resistance. For higher quality liquid metal, usually with lower lumped parameter (sigma alpha), the types of solid inclusions have less influence on specific cake resistance. (c) 2006 Springer Science + Business Media, Inc.