Copper, iron, and manganese oxides were added separately to melts of BaO-MgO-Al2O3-SiO2 glasses up to a maximum of 5 mol%, than devetrified at 100 degrees C for 1 h. The transition cations acted as fluxes on the glass properties by reducing the temperature of glass transition and the exothermic crystallization peak temperature. The activation energy for crystallization was slightly reduced, remaining in the feldspatic phase range. The effects on other properties, such as hardness and toughness, were evaluated in terms of indentation tests and related toation field strength and heating treatment. The presence of copper and manganese oxides inhibited the formation of hexacelsian crystals in the glass-ceramics, thus avoiding dangerous dimensional stress due to phase transformation. The complex evolution of the remaining crystalline phases is discussed in light of XRD, FT-IR, and SEM observations. (C) 2000 Elsevier Science Ltd.