Zinc isotope fractionation in liquid brass (Cu-Zn) alloy: potential environmental and archaeological applications

Abstract

Abstract A preliminary study of zinc isotope fractionation in brass melting suggests that the process can be modelled by simple Rayleigh fractionation. Brass melting experiments at 1100°C followed by quadrupole ICP-MS isotope ratio measurements of the resulting alloys suggest that the model is appropriate and that a useful approximation of the fractionation factor (α) is 1.0064. The data indicate that the change in isotope ratio of the residual liquid alloy would be measurable for zinc losses by evaporation of more than about 30 wt.%. It is unlikely that measurements at the precision of the current study (∼0.55‰amu −1 ) would be sufficient to distinguish between the two principal historical brass-making processes, although more precise measurement using a multi-collector ICP-MS probably would be. The experimental data also suggest that zinc vapour evolving during the evaporation of the first few per cent of the metal will be significantly fractionated (∼1.5‰amu −1 ) with respect to the liquid. This might provide a basis to distinguish between environmental zinc from high-temperature industrial processes and that derived from natural and manufactured product sources.