Andreia Ruivo, Maria Luísa Botelho, and António Pires de Matos,
Unidade de Investigação VICARTE
The red colour of glasses with gold and copper depends on several factors: metal concentration, reducing conditions, and temperature and time of the heat treatment process; this determines the dimension of the nanoparticles formed and then the colour of the glass which is due to a surface plasmon resonance band observed in the absorption spectra. For several years these glasses have been studied. Torung Bring states that gold ruby studies are focused on the impact of additives on colour development, ultimately aiming at a self striking glass, and studies of copper ruby glass concentrated mainly on the impact of different heat treatment conditions and different reducing agents. (1) In a previous work the authors synthesized gold ruby glass 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. (2) In another study copper nanoparticles were formed inside Cu ion-doped glass after infrared irradiation by a nanosecond laser and successive annealing at 700 °C for 1 h. (3) In a recent work nanoclusters formation were observed in copper doped silicate glasses after UV-light irradiation followed by thermal annealing. The glasses contained a small amount of stannous oxide (4). In this work a new process to obtain copper ruby glass was developed. Several copper ruby glasses were made by irradiating soda-lime silicate glasses, with different concentrations of copper, with gamma rays and further heating. No reducing agent was used as for example stannous oxide. Different colours were obtained by controlling the temperature and heating times. The more intense red colour was obtained using 1.0% (w/w) of Cu2O, with a heat treatment at 700 ºC during 120 minutes. Irradiation of a glass containing copper in oxidation state 2+ did not give any nanoparticles. A comparison of this process with the conventional ones and with recent works using a nanosecond laser and UV radiation is discussed. References (1) T. Bring, Doctoral Thesis in Chemistry, Vaxjo University, Sweden 2006 (2) A. Ruivo, C. Gomes, A. Lima, M. L. Botelho, R. Melo, A. Belchior, A. Pires de Matos. J. Cult. Herit. 9 (2008) e134ee137 (3) C. Silva, J. M.P. Coelho, A. Ruivo, A. Pires de Matos, Mater. Lett. 64 (2010) 705–707.