Introduction

Glass is produced by melting together silica, usually in the form of sand, and an alkaline flux such as soda or potash, with the addition of other ingredients. Glass was known to the ancient Egyptians though the technique of blowing glass was not introduced until the Roman period. The construction of glasshouse and furnace altered considerably over the years. The spectacular English contribution was the lofty brick glass-cone, which acted as a chimney for the furnace but also housed the glassmakers, who worked in teams around the furnace in the centre. The inside the cone, describes the basic glassmaking techniques, and explains the mysteries of the rich vocabulary that surround this ancient craft.

 Glass is an artificial, non-crystalline material, categorised as a super-cooled liquid rather than a solid .As mentioned above the basic ingredient is silica, usually in the form of a fine sand, to which alkaline fluxes such as soda or potash are added which bring the melting point down to the region of 1300 to 1500 degrees C. At this temperature the glass is fluid like water but before working the temperature is reduced until the glass has the consistency of honey or treacle .Other ingredients in the batch, as the mixture of raw materials is called, include lime or lead oxide, according to the type of glass being made, and a quantity of cutlet (broken glass), which aids fusion and saves on the costs of fuel and raw materials.

To colour glass, minute quantities of metallic oxides are added to the batch. About 50 BC it was discovered that molten glass could be blown into a bubble on the end of a long hollow metal pipe, and  present day. After completion all glass has to be annealed, a very gradual uniform cooling process which strengthens the glass by removing the stresses that have built up during manufacture. It is only after annealing that glass is ready to be decorated by techniques such as engraving or cutting. A close natural equivalent to glass is the translucent colourless quartz, rock crystal. Its qualities have been admired and imitated by glassmakers for centuries and to- day the word crystal is widely used to describe the best-quality clear glass. Top

EARLY HISTORY

 The Roman author Pliny, writing in the first century AD, tells a delightful story about how glass was invented. Some Phoenician sailors camped one night on a beach, lit a fire and set their cooking pots on blocks of natron (soda), which was the cargo they were carrying. When they awoke the following morning they found that the heat of the fire had fused the sand and natron into glass. But nobody knows for certain how glass originated. The earliest traces have been found in
Mesopotamia from the period 3000 to 2000 BC and from there the art probably spread to ancient Egypt. Before the discovery that glass could be blown on the end of a long hollow pipe, various forming techniques were used, such as casting and pressing into moulds, and carving from solid blocks of glass. About 1500 BC the Egyptians began using a technique called core moulding to make small vessels for precious ointments and liquids. A core was made from mud and straw or clay in the shape of the object required and was attached to the end of a metal rod. It was then dipped in molten glass and trailed with different colours or it was coated with powdered glass and fired. Once the glass had cooled the rod was withdrawn and the core picked out. This technique continued well after the invention of glassblowing. Under the Romans glassmaking flourished, spreading from its traditional home in Egypt and Syria to new corners of the empire such as Germany, France and even Britain. Top

By far the most significant event was the invention of glassblowing, which is thought to have occurred in Syria about 50 BC. It led not only to a new style of glass but also to a great increase in production, so that from being a luxury product glass became for the first time a common everyday article which it was not to be again until the nineteenth century. Cups, bowls, bottles, jars, jugs and vases formed the majority of the output. Roman  glass often has a green or brown tint due to impurities in the raw materials but in the second century AD it was discovered that those could be neutralised  by the addition of a small amount manganese oxide.

THE TWENTIETH CENTURY

 In the twentieth century there have been such spectacular advances in glass technology that glass is now being used in areas that would have been inconceivable one hundred years ago. One striking example is heat-resistant ovenware, which was introduced in 1915 by the Coming Glass Works in the USA under the famous brand name Pyrex. The borosilicate glass from which it is made has good chemical stability and low thermal expansion and can therefore withstand sudden changes in temperature. In the late 1950s a new material was developed, known as Glass Ceramics, which, like borosilicate glass, is extremely resistant to thermal shock. Its strength comes from the fact that a certain amount of crystallization is allowed to take place during the cooling of the molten glass, and its applications include cooker hobs and windows for coal and gas fires. Perhaps the most important technical breakthrough has been the introduction by Pilkington Brothers of St Helens in 1959 of the float glass process for the manufacture of flat glass.

Before float was invented, most flat glass had to be ground and polished after annealing to remove distortions on the surface caused by the manufacturing process. In the float glass process, a continuous ribbon of molten glass from the furnace floats along the surface of a bath of molten tin in a carefully controlled atmosphere. This not only produces a perfectly flat glass because the molten tin is flat, but it makes the laborious grinding and polishing stage redundant because the glass has become sufficiently hard by the time it leaves the molten tin for its surface not to be marked by the rollers on which it is taken up and conveyed to the annealing chamber. Float glass has revolutionised the flat glass industry and is now used worldwide under licence from Pilkingtons. Top