The aim of this study was to determine the effect of some chemical materials on the physical and chemical properties of dental stone. Accordingly, three types of chemical materials (rosin, nigella stavia oil and sodium lauryl sulfate) were incorporated into three kinds of type III dental stone (Zeta, Elite and Dental stone) at four concentrations. The physical properties evaluated were water-powder ratio, setting time, setting expansion, compressive strength and hardness. The evaluation of chemical properties was done by the use of infrared and ultraviolet spectrophotoscopy.The results...