2% solution of potassium sulfate is used as a surface hardening agent for:: (A) Casting stone, (B) Dental plaster, (C) Dental stone, (D) Type IV gypsum
Answer is B. Agar, a polysaccharide extracted from certain types of seaweed, is the main active ingredient in the material, while water is the major constituent in the agar impression material. A small percentage of borax is added to strengthen the gel. Since borax is a potent retarder for the setting of gypsum, an accelerator such as potassium sulfate is added to counteract the effect of borax.