the cylindrical portions of an upper mold part 12 a which form cylindrical cavities i e the cylinders in the engine block are then coated with a coating 14 containing a halogen such as fluorine in this example the halogen is fluorine and the coating material contains dipotassium fluorotitanate powder k 2 tif 6 other halogen containing compounds such as a mixed potassium chloride u2014 magnesium chloride eutectic potassium borofluoride or aluminum chloride may alternatively be used the k 2 tif 6 powder is mixed with a solvent a filler material such as zircon powder and a gelling agent the coating material for example may comprise 60 weight percent powder the powder comprising 25 weight percent zircon flour and 75 weight percent k 2 tif 6 dry milled powder and 40 weight percent ipa solvent the coating is typically sprayed onto the mold surface but may also be painted onto the mold alternatively dry k 2 tif 6 powder may be rubbed onto the mold surface or even added directly to the sand used to form the mold at levels of approximately 0 5 weight percent k 2 tif 6 the mold parts 12 a and 12 b are clamped together to form a mold cavity and molten aluminum silicon alloy is pored into the mold cavity the mold is then allowed to cool until the alloy has solidified the as cast engine block 10 is.