Sodium alginate is one of the basic ingredients of alginate impression materials. Experimental sodium alginate was made by using an immersion method in acid to extract Sargassum brown seaweed species. The sodium alginate powder was then tested for its purity and viscosity. The experimental sodium alginate had a purity determined by high-performance liquid chromatography equivalent to that of a standard sodium alginate powder (SIGMA A2158). The Brookfield viscosity test showed that the viscosity of the experimental sodium alginate was too low (45.3 mPas) and unsuitable for use as a dental alginate impression material basic ingredient.