A temperature-specific compound applied to refractory substrates having molten metal-contacting surfaces creates a chemically active and viscous surface that dramatically increases the ability of the treated substrate to remove slag, dross and other inclusions from a base metal alloy as it passes through or contacts the substrate. The refractory substrates include molten metal filters used by foundries and metal casters such as reticulated ceramic foam, cellular/honeycomb, silica mesh, and others that rely on their physical or sieving ability to remove particulate impurities from the base alloy being cast. The chemically active surfaces significantly increase filtration efficiency through a treatment process tailored to the specific chemistry of the alloy being filtered, such as ferrous metals that include iron, steel and more. Other refractory substrates such as aluminum oxide, magnesium oxide, zirconium oxide, aluminum silicate, silicon carbide (as common with reticulated ceramic foam filters) and the like may also include the coatings.