In this paper, colouration of the tin side of commercial soda-lime-silica float glass by copper ion exchange is described and characterised. Data on the resulting concentration versus depth profiles, absorbance versus depth profiles, UV-Vis spectra and CIE-Lab colour coordinates are reported. Fundamental aspects of the process of colouration are described and discussed. Optimum saturation of the colour is achieved after ion exchange at 520°C for 10 h or at 500°C for 20 h. The depth of the coloured layer increases with increasing treatment time. At the same time, a linear dependency is found between the values of a and b in the CIE-Lab colour space for variations of treatment time and temperature. The later indicates broad tunability of colouration between different shades of ruby and varying colour saturation. It is shown that colour arises from a redox reaction between copper species and residual tin ions, and that the depth of the coloured layer is governed by the position of the tin hump. The critical concentration of tin and copper to achieve colour formation was found to be ∼0·25 mol% and >1 mol%, respectively.