Shows that difficulties with shadowgraph techniques of Horton-Rodgers-Lapwood convection (HRLC) can be overcome by constructing porous media in which the interfaces between solid and liquid are either parallel or perpendicular to the confining boundaries of the experimental system. Rayleigh-Benard convection (RBC); Schematic diagrams of the rectangular porous medium, the random medium and the shadowgraph apparatus; More.