Abstract: A lost positive pattern comprising an open-pored plastics substrate containing pores with an average width of from one to three millimeters is used, in which, after a negative pattern has been made, the voids which it, as a core, contains are filled with metal by casting and the negative pattern is removed. The production of the negative pattern is preceded by the following method steps in which once the substrate of plastics material has been cleaned, it is wetted throughout with a keying resin film which partially dissolves the structure of its surface and in which at least one coat of an auto-crosslinking two-pack silicone is applied onto and into the whole of the substrate of plastics material to thicken the walls and/or the interlinking webs of the porous substrate of plastics material.

Abstract: Open-celled metal structures are produced which have walls and webs of uniform strength throughout. The structures may also have an irregular surface pattern. To make a strengthened positive pattern, the method comprises application of at least one layer of a strengthening agent such as poly(methyl methacrylate) or polyester resin to a plastic substrate used for ceramic mold formation. The strengthened positive pattern is embedded in a ceramic mass, and heated to incinerate and remove the plastic substrate, which results in voids in the ceramic mass. Molten metal is poured into the ceramic mass. After solidification, the ceramic mass is removed to form the open-celled metal structure.