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What is glass anyway?


The word "glass" comes from the proto-Germanic "glasa" which meant "the shiny" or "the gleaming". It is collective term for amorphous solids. Amorphous materials do not have a fixed atomic structure. Glass is always somehow associated with melting and setting. Scientists find it difficult to agree on an accurate definition, but as a minimum, one can say that glass is an inorganic melting product that essentially sets without crystallising. The earliest known recipe for glass was written around 650 BC, and says: to make glass, take 60 parts of sand, 180 parts of seaweed ash and 5 parts of limestone. The current recipe for flat glass is: 60 percent sand, 20 percent soda and sulphate, 20 percent dolomite and lime. These five ingredients form a completely homogeneous melt at around 1400 degrees Celsius.

It all began in the Near East ....

When we think of those things in our lives which we can barely imagine living without, we often find ourselves asking: where does it actually come from? Who invented it, and why? There is no detailed evidence for when precisely glass was made for the first time. It seems certain that it was probably the product of chance, but not all experts agree. The oldest finds date from the Mesolithic period around 7000 BC. The prototype glass was probably obsidian, a naturally occurring, hard, volcanic mineral glass, which was primarily used for tool making. The deliberate and organised manufacture of glass began about 4000 years later. Glass jewellery and the first glass vessels were produced around 3000 BC. Sometime around that period, people began to apply a protective glass coating to clay pots, hence the word 'glaze'. It is possible that someone may have wondered how this material would behave without a clay base: could the glaze exist by itself? Yes it can! As of 1500 BC the Egyptians first succeeded in producing hollow glass in the form of ointment jars and oil containers. This was achieved by pouring the molten glass into a sand mould.

All clear? Not quite ...  

Today we usually think of glass as a clear substance. Whether you gaze into a wine glass or through a window pane – you can usually see straight through it. Yet, that has not always been the case. Until about 100 AD no one was able to produce perfectly transparent glass, it was always coloured. Moreover, this type of glass was still very soft – the achievable smelting temperatures were simply too low. Shallow dishes and small vials epitomised the technological potential at that time. Larger containers, such as carafes and thin-walled drinking vessels only became possible after the invention and refinement of the so-called glass blower's pipe. Suddenly, glass became a material for containers that could be formed to suit any taste. The introduction of non-coloured glass and the improved quality that resulted from higher melting temperatures revolutionised glass making. Increasingly, glass was seen as a luxury product due to the inclusion of often work-intensive decorative touches. In addition, the craftsmen were able to cope with the "pressure of quantity demand" because models made of wood, stone or iron could now be reused.

Incidentally, the glass blower's pipe is a tube of up to one and a half metres in length with a mouthpiece on one end. The pipe works on the "soap bubble principle": a small piece of molten glass is taken up on one end which is then increased in size and worked by blowing and rotation. Glass blowing enables the production of standardised, thin-walled forms. Traditional craftsmen still use this method today, for example in the production of glass baubles for Christmas trees.

Glass from Rome and Venice ...

The ancient cities of Sidon and Alexandria were among the earliest glass making centres. In Sidon, in what is now the Lebanese Republic, the Phoenicians introduced mass production methods for glass.  The glass works there were also the first to produce almost transparent glass. Glass exports flourished. The material was exported to Rome where glass works were established. The greater the extent of the Roman Empire, the more widespread this desirable material became. The art of glass making soon arrived in what are now France, the Czech Republic and England. In the Mediaeval period, Venice, a trading metropolis, became the most important glass-making centre. Venetian glass makers reached the zenith of their creativity from the 15th to the 17th century. Their crowning achievement was the invention of crystal glass (cristallo), prized for its peerless brilliance and total lack of colour impurities. In old trade registers, the Venetian glass craftsmen are often listed as "phiolarius", which means something like "bottle maker". Today the island of Murano has become a byword for Venetian glass.

Glaze the windows ...

Right up to the Gothic period, glass was considered suitable for handicrafts but not for construction. That all changed in the 14th century. It is believed that a glass maker from Rouen in France perfected the manufacture of crown glass in 1330. Today it is sometime known as "bullseye glass". Crown glass is made by forming a plate from a thin, pre-blown sphere which is re-heated several times during the process. Another method is to spin it to create a round flat disk and cut it into sickle-shaped segments. Only the central section, with a diameter between seven and fifteen centimetres, is used for the pane: this is the "bullseye". Windows made of crown glass look as if a number of bottle bottoms have been placed next to one another and joined using lead strips. In addition to the crown glass method, there are the casting and cylinder methods.

Impressive, ostentatious, flooded with light ...

It was during the 17th century that glass finally became firmly established as an industrial material and construction element. Roller technology was introduced, which enabled the production of glass elements of a consistent thickness by pouring molten glass onto a rolling table, spreading it out and pressing it with heavy rollers. The demand for cut glass and glass decorations began to increase steadily. The relevant technologies were largely unknown in Venice, the traditional glass making centre. But people wanted bespoke glass – they wanted to integrate hunting scenes, landscapes and allegorical figures into their windows and glass vessels and have them flood with light. It was then that the so-called Baroque cut glass made its début. Artists and craftsmen from Bohemia, Silesia and Brandenburg began inscribing various motifs into glasses, and successfully challenging Venetian dominance.

Preferably totally flat ...

Glass production became fully automated, in the wake of industrialisation, a development that was accompanied by scientific studies into the physical properties of various glass recipes. The result was a steady improvement in manufacturing methods and an increasingly varied product range. 1904 was a special year for the glass industry. Together with Émile Gobbe, Émile Fourcault invented a way of producing flat glass – the so-called "Fourcault process". From then on, flat glass was manufactured with a consistent width because it was extracted vertically directly from the glass trough. Until then, window panes could only be fashioned in a highly work intensive and costly process from large glass cylinders, which had to be cut from top to bottom and heated multiple times in a special kiln before being stretched and pressed flat. Fourcault's "drawn glass" production method continued to be used in the flat glass industry for many years. The American Irving W. Colburn developed the Libbey-Owens process in 1917, which was essentially based on the Fourcault process. However, by modifying certain aspects of the process, Colburn was able to achieve a fortyfold production increase. The first fully automated bottle blowing machine was introduced in 1923. In 1959, the British firm Pilkington Brothers Ltd. presented a process for the production of float glass. Today, float glass is still the most widely used glass type in construction. The production process involves a continuous ribbon of molten glass which is poured onto a bath of molten tin and floats on the surface due to its lower specific gravity.

Glass here and now, and in the future ...

Glass is eternal and ubiquitous. Throughout the ages and generations it has developed from a chance by-product to a multi-functional production material. And, there appears to be no end in sight to this development. Today, glass is used as a structural element, an insulating material and, in the form of glass fibres, in the communications industry. Solar panels, displays and even semiconductors are made of glass. Products stored in hygienic, clean glass casings remain fresh and retain their flavour and unadulterated aroma for extensive periods: nothing gets in; nothing gets out. That applies to the perfume industry as well as medical engineering. In fact, there are very few sectors today that can get by without glass. The glass industry is continuously developing new application possibilities using cutting-edge technology and the newest scientific insights. Today the market still differentiates between mundane glass for daily use, special purpose glass and ornamental glass.