Amorphous precipitated high structure silica pigment useful in the reinforcement of silicone rubber is described. The silica pigment is treated with an aqueous solution of a metal, e.g., calcium and barium, which forms a relatively water insoluble, white or colorless sulfate salt in amounts sufficient to provide at least an equal molar amount of the metal compared to the amount of alkali metal in the silica. Silicone rubber reinforced with such silica pigment exhibits a water swell of less than 4 volume percent.