ixture comprising sources of alkali metal oxide, an oxide of silicon, water, pyrrolidine, and a tetraureacobalt (II) complex and having a composition, in terms of mole ratios of oxides, falling within the following ranges: SiO2 /Al2 O3 =5-infinity H2 O/SiO2 =1-3000 OH-/SiO2 =0.001-10 M/SiO2 =0.01-3 R/SiO2 =0.01-5 R'/SiO2 =0.005-2 wherein M is an alkali or alkaline earth metal cation, R is pyrrolid