Historically, glazing of ceramics developed rather slowly, as appropriate materials needed to be discovered, and also firing technology able to reliably reach the necessary temperatures was needed. Glazes first appeared on stone materials in the 4th millennium BC, and Ancient Egyptian faience (fritware rather than clay-based) was self-glazing, as the material naturally formed a glaze-like crust in firing. Glazing on true pottery followed the invention of glass around 1500 BC, in the Middle East and Egypt with alkali glazes including ash glaze, and in China, using ground feldspar. By around 100 BC lead-glazing was widespread in the Old World.