With the aim to study the chemical response of selected glass samples to an underwater medium, accelerated ageing tests were undertaken in the laboratory by immersing the samples into a solution, which simulates the average composition of sea water. Tests were conducted both at low (-15 degrees C) and high (40 degrees C) temperature for several time cycles. The main goal of the research was to study, through different observation and analytical techniques, chemical alteration mechanisms as a function of the glass compositions and experimental conditions (e.g., temperature, time). Results showed that glasses experience a recurrent decay process, which starts at a neutral pH medium with leaching of alkaline ions and concludes at a basic medium, as a consequence of hydrolytic attack, with destruction of glass network and loss of main forming oxides. The research has,thus provided outstanding data that will be useful for future conservation and restoration of historical glasses preserved in an underwater medium. (c) 2005 Elsevier B.V. All rights reserved.