A new patented casting process is described, based on a precision aggregate mold, bonded with a water-soluble binder. For the first time the twin functions of the mold (i) defining shape and (ii) providing cooling have been successfully separated allowing the production of castings of all sizes and shapes (thin and thick walls) for all Al and Mg alloys. Because solidification and cooling are separately controlled by the application of water a number of advantages follow immediately. The mold is ablated (i.e. eroded) away by the water without fume or dust and the ‘air gap’ is eliminated by direct contact with the water, enhancing the rate of solidification to levels normally unattainable, resulting in significantly enhanced properties. The unusual microstructures of Al-Si alloys having large DAS but micron-sized eutectic silicon indicates, in agreement with earlier predictions, that DAS per se does not control strength or ductility. The process is currently proving itself in commercial operation, having the additional advantages of modest start-up and tooling costs as well as low competitive piece part costs because of the use of low cost materials and the recycling of aggregate and water.