A successful procedure has been worked out for the subsequent colouration of low-alkali borosilicate glass that comprises silver doping by silver/sodium ion exchange below the glass transformation temperature followed by thermal processing well above, at 750 degrees C. The particle formation process as studied by electron microscopy and optical spectroscopy revealed the formation of silver nanoparticles proceeding via silver oxide intermediates. The intermediate nanoparticles are supposed to result from a phase separation within the silver ion-doped glass. Their formation and succeeding transformation to silver nanoparticles upon thermal processing is accompanied by characteristic absorption peaks in the visible range which gradually convert to the surface plasmon resonance of spherical silver nanoparticies. The optical density of the silver-based colouration achieved this way assumes values comparable to those usually obtained with soda lime silicate glass. (C) 2008 Elsevier B.V. All rights reserved.