We know nothing or very little about blast furnaces before the invention of the blow-rod in the 1st century B.C.. From that moment and until the 7th-8th century, glass production grew in an almost industrial sense. Big tank furnaces were used (the remains of some of them have been found in Palestine and Egypt) which could produce up to 10 tonnes of glass. Once the fusion was finished, which lasted several days if not weeks, the furnace was put out, demolished, and the big sheet of rough glass (its thickness was several tens of centimetres), was broken into blocks. These were transported to other places where the glass was remelted into crucibles situated in small furnaces to be moulded. In the middle ages and until the advent of the industrial era, the mixture was calcinated beforehand at about 800°C in reverbatory furnaces, transformed into frit which was then melted in crucible furnaces.