The effect of melting temperature, time, and the type of raw material, NaNO3 or Na2CO3, as a source for Na2O on the glass formation for a Na2O.4TeO(2)(NT4) melt was investigated. Melting with NaNO3 at 750degreesC for a short time (15 min) produced a glass that is slightly more chemically durable and more resistant to crystallization than glasses melted at a higher temperature (800degreesC), or for a longer time (60 min), or using Na2CO3. A thin surface layer (<1.5 nm) that contains some nitrogen and a higher concentration of bridging oxygen is suspected to be the reason for the higher chemical durability and higher resistance to crystallization for this glass. However, melting at 800degreesC for 60 min produced a glass, whose properties were independent of the type of raw material, NaNO3 or Na2CO3, used. (C) 2004 Kluwer Academic Publishers.