About Glass

Modern life just would not be possible without glass. From the jar that holds the morning marmalade, the mirror in which we brush our teeth, the windows and car windscreen we look through, the computer screen many of us use at work every day to the light bulb we switch off last thing at night; glass is around us everywhere.

But what is this amazing substance, where does it come from and how is it made?

What is glass?
Glass is a combination of sand and other minerals that are melted together at very high temperatures to form a material that is ideal for a wide range of uses from packaging and construction to fiber optics.

A form of glass occurs naturally within the mouth of a volcano when the intense heat of an eruption melts sand to form Obsidian, a hard black glassy type of stone. Man first used this as tips for spears.

Today man has mastered the glass-making process and can make many different types of glass in infinitely varied colors formed into a wide range of products.

Glass, chemically, is actually more like a liquid, but at room temperature it is so viscous or 'sticky' it looks and feels like a solid. At higher temperatures glass gradually becomes softer and more like a liquid. It is this latter property which allows glass to be poured, blown, pressed and molded into such a variety of shapes.

How glass is made?
Glass is made by melting together several minerals at very high temperatures. Silica in the form of sand is the main ingredient and this is combined with soda ash and limestone and melted in a furnace at temperatures of 1700oC. Other materials can be added to produce different colors or properties. Glass can also be coated, heat-treated, engraved or decorated.

Whilst still molten, glass can be manipulated to form packaging, car windscreens, glazing or numerous other products. Depending on the end use, the composition of the glass and the rate at which it is allowed to cool will vary, as these two factors are crucial in obtaining the properties the glassmaker is seeking to achieve.

Glass Forming

Like treacle, glass is fluid at high temperature and its fluidity decreases as the temperature is reduced. Unlike water, glass has no specific melting or freezing point but is gradually changed from a solid to a liquid as the temperature is increased. It is this property of 'variable viscosity', which is used in forming a mass of glass into articles of beauty or utility.

Glass Blowing
Making Glass Containers by Automatic Process
Flat Glass
Glass Fibre Manufacture
Optical Fibre Manufacture
Glass Tubing
Automatic Domestic Glassware Production
Electric Light Bulb Production
Secondary Processing

Glass Blowing
For nearly 2,000 years glass blowing by hand was the main method of forming glass articles. The last few years of the 19th century saw the beginnings of blowing glass by compressed air and the 20th century brought in the revolution of mechanization, although glass blowing is still carried out by craftsmen today.

For glass blowing, a hollow blowing-iron or pipe is dipped into a pot containing molten glass and the glass is gathered at the end of the pipe by rotating it, similar to gathering treacle onto a spoon. The collected glass, known as the 'gather', cools to about 1000oC and is marvered (rolled on an iron slab) to form a 'parison'. The parison is then manipulated by allowing it to elongate, re-heating it and blowing air into it to bring it into a shape that resembles the final article. It is then placed in an iron or wooden mould, which is kept wet by water and the glass, is blown to the final shape of the interior of the mould. There is no contact between the glass and the mould, due to the water which forms a cushion of steam. During the blowing the pipe is rotated continuously, preventing mould joints or other mould imperfections appearing in the glass.

Making Glass Containers by Automatic Process
Until the second half of the 19th century bottles were made by hand gathering, blowing and finishing the neck. A semi automatic method of bottle making was developed after 1850 but this has since been replaced by the fully automatic process. All bottles and jars are now made automatically by one of two methods - 'Press and Blow' or 'Blow and Blow'.

Flat Glass
The main flat glass products are for high quality glazing in homes, offices, hotels, shops, vehicles public buildings and glass for horticulture; wired glasses for fire resistance; patterned glass for privacy and decoration; and a wide range of glass for environmental control and energy conservation.

Other uses for flat glass include toughened glass doors, suspended window assemblies, cladding for the exterior of buildings, mirrors and low-reflection glass for pictures and instrument dials. The two manufacturing processes for producing flat glass in the UK are the float glass and rolled glass processes.

Glass Fiber Manufacture
There are two main groups of glass fiber products: continuous glass fiber which is used for the reinforcement of plastics, rubber and cement; and glass wool, which is used for thermal insulation and which is produced by the Crown process

Optical Fiber Manufacture
Communications are increasingly based on electro-optic systems in which telephones, television and computers are linked by fiber optic cables which carry information by laser. Making glass optical fibers is a highly specialized aspect of glas 

Glass Tubing
Glass tubing is used in many products including scientific instruments, fluorescent lights and many other lighting applications. Glass tubes are made by the Danner Process or the Vello Process.

Automatic Domestic Glassware Production
Tumblers, wine glasses and pint pots are made using the Westlake machine which was originally developed for blowing bulbs for domestic lamps and radio valves. It has since been adapted for making drinking glasses at a rate of up to 55,000 a day.

Electric Light Bulb Production
The ribbon machine was developed for the high-speed manufacture of bulbs for domestic lamps, auto lamps and vacuum flasks

Secondary Processing
As part of the production process some types of glass are subjected to secondary processing such as annealing, toughening, coating and decorating.

History of Glass

A Brief History of glass
From our earliest origins, man has been making use of glass. Historians have discovered that obsidian - natural glass made within the mouth of a volcano when the intense heat of an eruption melts sand - was first used by man as tips for spears.

The oldest examples of glass were in the form of Egyptian beads, dating from 12,000 BC. It was not until 1500 BC that the first hollow glass container was made by covering a sand core with a layer of molten glass.

Glass blowing became the most common way to make glass containers from the First Century BC. However, the glass made during this time was highly colored due to the impurities of the raw material. It was not until the First Century AD when colorless glass was produced and then colored by the addition of coloring materials.

The secret of glass making came to Britain with the Romans. However, the skills and technology required to make glass were closely guarded by the Romans and it was not until the Roman Empire disintegrated that skills for glass making spread throughout Europe and the Middle East.

The Venetians, in particular, gained a reputation for technical skill and artistic ability in the making of glass bottles and a fair number of the city's craftsmen left Italy to set up glassworks throughout Europe.

In Britain, there is evidence of a glass industry round Jarrow and Wearmouth dating back to 680AD, while from the 13th Century; there is evidence of there having been a glass industry in the Weald and the afforested area of Surrey and Sussex around Chiddingford.

A major milestone in the history of glass occurred with the invention of lead crystal glass by George Ravenscroft. He attempted to counter the effect of clouding that sometimes occurred in blown glass by introducing lead to the raw materials used in the process.

The new glass he created was softer and easier to decorate and had a higher refractive index, adding to its brilliance and beauty, and it proved invaluable to the optical industry. It's thanks to Ravenscroft's invention that optical lenses, astronomical telescopes, microscopes and the like became possible.

The modern glass industry only really started to develop in Britain after the repeal of the Excise Act in 1845 relieved the heavy taxation that had been enforced. Before that time, excise duties were placed on the amount of glass melted in a glasshouse and levied continuously from 1745 to 1845.

Joseph Paxton's Crystal Palace at the Great Exhibition of 1851 marked the beginning of the discovery of glass as a building material. The revolutionary new building encouraged the use of glass in public, domestic and horticultural architecture. Glass manufacturing techniques also improved with the advancement of science and better technology.

By 1887 glass making developed from traditional mouth blowing to a semi-automatic process when Ashley introduced a machine capable of producing 200 bottles per hour in Castleford, Yorkshire - more than three times quicker than the previous production methods.

Twenty years later, in 1907, the first fully automated machine was developed in America by Michael Owens from major glass manufacturers Owens of Illinois, and used at its factory in Manchester, Illinois making 2,500 bottles per hour.

Other developments followed rapidly, but it was not until the First World War, when Britain became cut off from essential glass suppliers that glass became part of the scientific sector. Up until then glass was seen as a craft rather than a precise science.

Today, glass making is a modern, hi-tech industry operating in a fiercely competitive global market where quality, design and service levels are critical to maintaining market share.

Modern glass plants are capable of making millions of glass containers a day in many different colors, but green, brown and clear remain the most popular.

Few of us can imagine modern life without glass. It features in almost every aspect of our lives - in our homes, our cars and whenever we sit down to eat or drink. Glass packaging is used for many products, wines, spirits and beers all come in glass as do medicines and cosmetics not to mention numerous foodstuffs.

With increasing consumer concern for the environment, glass has again come into its own proving to be an ideal material for recycling. Glass recycling is good news for the environment. It saves used glass containers being sent to landfill and less energy is needed to melt recycled glass than to melt down raw materials, thus saving energy. Recycling also reduces the need for raw materials to be quarried thus saving precious resources.

The Future of glass
Glass as a material in its own right will always exist. But many new applications and manufacturing processes will involve glass in combination with other materials. Optical fibers, for example, are currently manufactured with one or more different coating, which are often plastics. With the increasing sophistication of opto-electronic devices, there is an increasing need to combine optical and electronic devices for many applications such as transmission of audio, video and data information. Glasses and ceramics, either alone or composite with other materials, will find increasing application in biological and medical areas. Materials such as photochromic, electrochromic and thermochrominc glasses, which respond to external stimuli, are being developed with various, sometimes unusual, applications.

Medical Information
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   • Silicates
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   • About Glass
   • Glass Forming
   • History of Glass
   • The Future of glass