Composite materials formed by metal nanoclusters embedded in glasses/glazes have been produced for centuries (Roman hematinum and Renaissance alassonti, Coptic lustre-painted glass and Islamic lustre ceramics). Comparisons were drawn from Raman analyses of alkali borosilicate glasses coloured by copper as 'blue' Cu 2+ (peak absorption at 750 nm), as 'colourless' Cu + and as 'opaque red' Cu 0 (peak absorptions at โผ420 and 570 nm). In particular, Raman analyses of copper-ruby glasses containing Cu 0 nanocrystals were performed with blue (488 nm), green (514.5 and 532 nm) and red (647.1 nm) excitation, providing information on the glass structure around the Cu 0 precipitate. Addition of europium to Cu 0containing glass melts yielded glasses that were dichroic; for example, a glass with 0.2 wt% Cu and 0.4 wt% Eu was red in absorbed light and blue in transmitted light. The backscattering Raman signature of the glassy silicate matrix containing copper indicated a less-polymerized network around the Cu 0 nanocrystals/atoms than around Cu 2+ or Cu + (Raman index of polymerization โผ1 instead of โผ2). Strong Rayleigh scattering is measured under blue excitation for all copper-containing glasses and under red excitation for Cu 0 -containing (red) glass.