Abstract: An improved process and product for supplying a protective atmosphere of carbon dioxide plus a minor percentage of sulfur hexafluoride (CO.sub.2 /SF.sub.6) by means of a solid agent consisting of solidified CO.sub.2 and SF.sub.6 which by sublimation in the presence of molten magnesium and its alloys provides a protective atmosphere of desired composition. This solid agent is used for maintaining a protective atmosphere within a covered vessel containing molten magnesium or its alloys. It is also used for purging a crucible and for flushing the air from a mold cavity prior to the pouring of the molten metal. The amount and the composition of the solid agent can be adjusted to provide the desired composition of protective atmosphere for a wide variety of situations involving molten magnesium.