slurries containing tri - or polyvalent cations are used for investment casting and making molds as well as core coatings . these slurries are aqueous or alcohol - based containing a mineral component and a polyanionic binder , where at least one of the continuous phase or mineral component contains trivalent or polyvalent cations or cations that are converted into trivalent or polyvalent cations during use . the cationic component is selected from a group consisting of at least one of the metals iron or aluminum . the polyanionic component contains at least one of the group consisting of colloidal silica or one or more water - soluble organic polymers .