The effect of Sb3+ and Sn2+ during the heat treatment of copper ruby alkali silicate glasses is investigated. The reducing power of SnO and Sb2O3 with respect to Cu is investigated and it is concluded that SnO has the strongest reducing capability. When Cu2O and SnO concentrations are low, minor additions of Sb2O3 have an observable impact on colour development and and absorbance, as thin pieces of glass develop a bluish tint and larger shift towards longer wavelengths is observed in UV/vis spectra. The differences in colour and spectra are suggested to be caused by differences in size of the colour agent, Cu metal particles.