The invention relates to a method for treating molten metal that is contained in a metallurgical vessel, according to which a fine-grained blanket material containing silicon oxide and aluminium oxide is spread over the surface of the molten metal. The aim of the invention is to prevent the formation of dust and to facilitate the distribution of the blanket material over the surface of the molten metal. To achieve this, the blanket material consists of a synthetic zeolite material, which contains essentially equal fractions of silicon oxide and aluminium oxide. Said blanket material comprises a close grain-size distribution, in such a way that less than 20% of the grains have a diameter of less than 30 μm or greater than 125 μm. According to an additional embodiment of the invention, a vegetable ash, in particular a rice chaff ash, can be added to the blanket material.