Abstract: A method of improving the quality of hot pressed Si.sub.3 N.sub.4 bodies is disclosed. Unpurified silicon powder and admixed oxygen carrying agents are compacted to form a preform. The preform is nitrided, facilitated by the presence of certain impurities, to agglomerate the mixture to an increased density no greater than 2.7 gm/cm.sup.3. The nitrided preform is immersed in one or more stages in one or more leaching solutions of effective concentration to remove the selected impurities. The treated preform is then hot pressed to full density accompanied by a substantial reduction or absence of undesirable impurities such as iron silicide, which can conventionally form during hot pressing.