In this work, a low-temperature thick-film dielectric consisting of a high-lead low-temperature glass with a reactive nanoscale filler is characterised to enable deposition of thick-film electronics onto substrates such as glass and metals (steel, aluminium, brass, titanium) which cannot be exposed to the standard high-temperature 850 C thick-film firing cycle. The dielectric is stabilised by reaction of the filler with the lead in the glass. For a TiO2 filler, we get : PbO (glass) + TiO2 (filler) -> PbTiO3. This reaction stabilises the dielectric both by increasing the filler volume fraction and by depleting the glass in lead thereby increasing its melting point. Examining different filler particle sizes, we show that using nanoscale fillers allow us to considerably increase the reactivity, yielding stabilised dielectrics onto which further layers such as conductors and resistors can be deposited.