Castable solids from Aremco (http://www.aremco.com/potting-casting-materials/) are convenient media for pressure transmission in multianvil geometries of complex shape. A zirconia-based castable ceramic, Aremco Ceramacast 646, is introduced and compared to MgO-Al₂O₃-SiO₂-based Aremco Ceramacast 584. Ceramacast 646 has some advantages over the widely used Ceramacast 584; these include ease of consistent fabrication and better thermal insulation. Some disadvantages are poorer efficiency in converting press thrust to sample pressure and slower quenching rates. Potential applications are informed by these differences.