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
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.
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.
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.
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.
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.
THE GLASS FORMING PROCESSES
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.
Making Glass Containers by Automatic Process
Glass Fibre Manufacture
Optical Fibre Manufacture
Automatic Domestic Glassware Production
Electric Light Bulb Production
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.
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
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'.
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.
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 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.
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
The ribbon machine was developed for the high-speed
manufacture of bulbs for domestic lamps, auto lamps and
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
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.
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
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
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.
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
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.
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.
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.
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.