A process for shielding molten metal of a casting stream in a casting apparatus from oxidation by the ambient atmosphere which comprises enclosing the casting stream in an atmosphere which consists essentially of a mixture of an inert gas such as nitrogen as a carrier and a reactive gas, such as a hydrocarbon, capable of reacting with oxygen in the melt. The gas atmosphere preferably consists of a mixture containing 5 to 20% by volume of the reducing gas, namely, the hydrocarbon, the balance being the carrier gas namely nitrogen. Any conventional technique can be used to ensure that the gas mixture covers the casting stream.