Gold nanoparticles in ancient and contemporary ruby glass

Gold ruby glass was made by irradiating a soda-lime-silicate glass with ca. 0.2 weight % of gold with gamma rays and further heating instead of using a reducing agent such as stannous oxide. Different colours were obtained by controlling the temperature and heating times. A comparison of this process to develop ruby glass with the conventional ones is discussed. Ruby glass was also made by dissolving gold metal in soda-lime-silicate glass and using stannous oxide at 1500 °C. The colour of the gold ruby glass is due to the presence of gold nanoparticles.A small purple-red 17th century glass vase was also studied and it was found to contain only manganese as the colouring agent; in this case the colour is due to electronic d–d transitions. A tentative experiment to reproduce the colour of this vase showed that the oxidation conditions are critical.