The recipe for making glass has changed little for several thousands of years: sand, alkali ashes, and lime from crushed stones are melted together to give a strong, yet fragile material. This molten material can then be manipulated by the glassmaker in a number of ways.This Italian vase, from around 1600, was mould blown. A bubble of molten glass is blown into a mould, determining the shape of the object, and in some cases, the surface decoration.