A favourable microstructure was tailored by controlled crystallization of a quenched glass made of a combination of metal industry slags and a lead bisilicate frit. The frit was used to simulate a lead-containing waste. In the devitrified glass microstructure, lead-rich glassy pockets were contained in an akermanite (Ca2MgSi2O7) crystalline matrix. Leaching of lead was reduced by a factor of two as a result of devitrification processing; the low-lead crystalline matrix protected the lead-rich pockets from chemical attack.