Glass making

Container glass were originally made by covering a clay core with molten glass, then removing the core when the glass cooled. When the blowpipe was invented about 100 B.C., glass-makers could create larger containers in a much shorter time. The new art of glass-blowing spread throughout Europe with the advance of the Roman Empire. After the fall of the Empire, glass-making centres were established in Europe

Container glass is made of simple, natural ingredients: silica sand, soda ash and limestone. These materials are mined existing in the nature.The basic recipe of sand, soda, and lime has not changed over the centuries, but many variations exist. For example, adding potash and lead improves the quality of glass, while introducing cobalt, sulphur, or other minerals produces colour. Broken glass, known as cullet, is added to the mixture of raw materials to accelerate the melting process. The ingredients for a batch of glass are mixed and melted in special large pots heated by a furnace.

To blow glass, the glass-blower dips the end of a hollow blowpipe through the "glory-hole" into a pool of molten glass in the furnace. The pipe is rotated until the right amount is gathered as a gob on the end, then withdrawn. By blowing through the pipe, the blower can create a rounded, free-blown bottle. The glass is then attached to the pontil iron and cut from the blowpipe. The object can be shaped by using a tool and wooden paddle. By blowing while the gather of glass is held within a mould, the same shape is achieved each time. After the final shaping, the object is placed in an annealing oven to slowly cool and harden.