its intended use a method is provided for making a composite mold body of sand particles and a wax composition such that the incidence of residual compressive or tensile stresses in an aluminum alloy casting is reduced a wax material is selected with a melting point such that heated regions of the mold body soften after the cast metal has formed a solid shell the invention may be applied in the casting of other light metal alloys a wax composition is selected for mixture with sand particles in forming a mold body or core surface waxes are soft polymeric materials that may be mixed with sand particles or deposited on sand particles from a suitable removable solvent in one embodiment a wax like material is identified by for example a simple experiment or experience to soften sand particles in a mold body the softening occurs due to the melting or softening of the sand and wax mixture due to heating from the cast metal a wax is selected that softens regions of the mold body against which the cast metal may be expected to shrink the melting point of the wax is selected so that the mold or core section may soften after a solid shell has formed on the cast metal and before the casting has hardened to the stage in which compressive or tensile stresses are frozen into the cast structure in casting of aluminum alloy castings for example it is found that polymer waxes melting in the region of about 225 u00b0 c to about 275 u00b0 c are often suitable as stated the selection of a specific wax for the casting of a specific casting alloy into a predetermined article shape may be made by trying different waxes in different mold bodies while.