B

Potassium sulfate (≈2 % by weight) is added to gypsum-based dental materials as an accelerator that shortens and controls their setting time; it does not act as a retarder. Studies show that incorporating K₂SO₄ into gypsum investments markedly decreases the setting time (while also slightly lowering expansion) compared with mixes made with water alone [Yan & Takahashi, 1998, PMID 10219144; Jarvis & Earnshaw, 1980, PMID 6940533].