Crystal formations obtained from evaporating clear filtrates of dental stone mixed with various solutions were examined with an optical and scanning electron microscope. It was found that when K2SO4 was present in any concentration, a spherulitic structure dissimilar to that of CaSO4 2H2O and K2SO4 was dominant. It is concluded that syngenite (a complex compound of CaS04 and K2SO4) forms at the center of the nuclei of crystallization and is responsible for spherulitic formation. The use of K2SO4 solution and saturated CaSO 4 solution was also found to improve the strength both at one and 24 h.
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