Sodium Alginate can react with calcium salts forming a heat - irreversible gel. It is widely used in impression material (Dental, Hand and Leg, study models, portraits etc). Normally for impression material Sodium Alginate is mixed with Calcium Sulfate (Gypsum), Tri Sodium Phosphate, Diatomaceous earth, Zinc Oxide, Potassium Titanium Fluoride etc.
Alginate impression materials are easy to use, less expensive, with quick setting time. It has low water content, steady viscosity and long shelf life. Alginates fine particle size makes impression surface smooth and thus more identical to the original mould.