historically, sulfur-containing compounds were the first materials used to dealkalize glass containers. dealkalization proceeds through the interdiffusion/ion-exchange of na out of the glass and h/ho into the glass, along with the subsequent reaction of the sulfate species with available sodium at the surface to form sodium sulfate (naso). the latter is left behind as water-soluble crystalline deposits, or "bloom", on the glass surface that must be rinsed away prior to filling. on manufacturing lines, one way in which this process was done was by flooding the annealing lehr with sulfur dioxide (so) or sulfur trioxide (so) gases—especially in the presence of water, which enhances the reaction. however, this practice fell into disfavor due to environmental and health concerns regarding so-type gases. an alternative method for sulfate treatment is with solid ammonium sulfate salt or aqueous solutions thereof. these materials are introduced inside the container after forming and decompose into gases in the annealing lehr, where the resulting sulfur-containing gas mixture carries out the dealkalization reaction. this method is purportedly safer than flooding the annealing lehr since the unreacted components in the gas mixture will tend not to escape to the atmosphere, but rather react with each other and recreate the original salt in the container that can later be rinsed away.