The aim of this proposal is to examine the pressure induced changes in the structure of two cobalt-bearing silicate glasses. Transition metals such as cobalt can adopt different structural roles depending on their valance state. Cobalt-bearing glasses synthesised under different oxygen partial pressures will be used for this experiment, studies of these glasses have shown that different valance states are accessed and the structural role of Co3+ and Co2+ is very different. The aim of this work is to evaluate how theses differently modified amorphous structures behave under pressure. Building on previously successful experiments at ISIS this work will involve study of two glass samples (with different amounts of Co2+ and Co3+) with diffraction patterns measured at 10 and 17GPa.