The Discovery of Glass
Natural glass has existed since the beginnings of time, formed when certain types of
rocks melt as a result of high-temperature phenomena such as volcanic eruptions,
lightning strikes or the impact of meteorites, and then cool and solidify rapidly. Stone-age
man is believed to have used cutting tools made of obsidian (a natural glass of volcanic
origin also known as hyalopsite, Iceland agate, or mountain mahogany) and tektites
(naturally-formed glasses of extraterrestrial or other origin, also referred to as
obsidianites).
According to the ancient-Roman historian Pliny (AD 23-79), Phoenician merchants
transporting stone actually discovered glass (or rather became aware of its existence
accidentally) in the region of Syria around 5000 BC. Pliny tells how the merchants, after
landing, rested cooking pots on blocks of nitrate placed by their fire. With the intense
heat of the fire, the blocks eventually melted and mixed with the sand of the beach to form
an opaque liquid.
This brief history looks, however, at the origins and evolution of man-made glass.
A Craft Is Born
The earliest man-made glass objects, mainly non-transparent glass beads, are thought to
date back to around 3500 BC, with finds in Egypt and Eastern Mesopotamia. In the third
millennium, in central Mesopotamia, the basic raw materials of glass were being used
principally to produce glazes on pots and vases. The discovery may have been
coincidental, with calciferous sand finding its way into an overheated kiln and
combining with soda to form a coloured glaze on the ceramics. It was then, above all,
Phoenician merchants and sailors who spread this new art along the coasts of the
Mediterranean.
The oldest fragments of glass vases (evidence of the origins of the hollow glass industry),
however, date back to the 16th century BC and were found in Mesopotamia. Hollow
glass production was also evolving around this time in Egypt, and there is evidence of
other ancient glassmaking activities emerging independently in Mycenae (Greece), China
and North Tyrol.
Early Hollow Glass Production
After 1500 BC, Egyptian craftsmen are known to have begun developing a method for
producing glass pots by dipping a core mould of compacted sand into molten glass and
then turning the mould so that molten glass adhered to it. While still soft, the
glass-covered mould could then be rolled on a slab of stone in order to smooth or
decorate it. The earliest examples of Egyptian glassware are three vases bearing
the name of the Pharaoh Thoutmosis III (1504-1450 BC), who brought glassmakers to
Egypt as prisoners following a successful military campaign in Asia.
There is little evidence of further evolution until the 9th century BC, when glassmaking
revived in Mesopotamia. Over the following 500 years, glass production centred on
Alessandria, from where it is thought to have spread to Italy.
The first glassmaking "manual" dates back to around 650 BC. Instructions on how to make
glass are contained in tablets from the library of the Assyrian king Ashurbanipal
(669-626 BC).
Starting to Blow
A major breakthrough in glassmaking was the discovery of glassblowing some time
between 27 BC and AD 14, attributed to Syrian craftsmen from the Sidon-Babylon area.
The long thin metal tube used in the blowing process has changed very little since
then. In the last century BC, the ancient Romans then began blowing glass inside moulds,
greatly increasing the variety of shapes possible for hollow glass items.
The Roman Connection
The Romans also did much to spread glassmaking technology. With its conquests, trade
relations, road building, and effective political and economical administration, the Roman
Empire created the conditions for the flourishing of glassworks across western Europe
and the Mediterranean. During the reign of the emperor Augustus, glass objects
began to appear throughout Italy, in France, Germany and Switzerland. Roman glass has
even been found as far afield as China, shipped there along the silk routes.
It was the Romans who began to use glass for architectural purposes, with the discovery
of clear glass (through the introduction of manganese oxide) in Alexandria around
AD 100. Cast glass windows, albeit with poor optical qualities, thus began to appear in the
most important buildings in Rome and the most luxurious villas of Herculaneum and
Pompeii.
With the geographical division of the empires, glass craftsmen began to migrate less, and
eastern and western glassware gradually acquired more distinct characteristics.
Alexandria remained the most important glassmaking area in the East, producing luxury
glass items mainly for export. The world famous Portland Vase is perhaps the finest
known example of Alexandrian skills. In Rome's Western empire, the city of Köln in
the Rhineland developed as the hub of the glassmaking industry, adopting, however,
mainly eastern techniques. Then, the decline of the Roman Empire and culture
slowed progress in the field of glassmaking techniques, particularly through the 5th
century. Germanic glassware became less ornate, with craftsmen abandoning or not
developing the decorating skills they had acquired.
The Early Middle Ages
Archaeological excavations on the island of Torcello near Venice, Italy, have unearthed
objects from the late 7th and early 8th centuries which bear witness to the transition
from ancient to early Middle Ages production of glass.
Towards the year 1000, a significant change in European glassmaking techniques took
place. Given the difficulties in importing raw materials, soda glass was gradually replaced
by glass made using the potash obtained from the burning of trees. At this point, glass
made north of the Alps began to differ from glass made in the Mediterranean area, with
Italy, for example, sticking to soda ash as its dominant raw material.
Sheet Glass Skills
The 11th century also saw the development by German glass craftsmen of a technique -
then further developed by Venetian craftsmen in the 13th century - for the production
of glass sheets. By blowing a hollow glass sphere and swinging it vertically, gravity would
pull the glass into a cylindrical "pod" measuring as much as 3 metres long, with a
width of up to 45 cm. While still hot, the ends of the pod were cut off and the resulting
cylinder cut lengthways and laid flat. Other types of sheet glass included crown glass
(also known as "bullions"), relatively common across western Europe. With this technique,
a glass ball was blown and then opened outwards on the opposite side to the pipe.
Spinning the semi-molten ball then caused it to flatten and increase in size, but only
up to a limited diameter. The panes thus created would then be joined with lead strips and
pieced together to create windows. Glazing remained, however, a great luxury up to
the late Middle Ages, with royal palaces and churches the most likely buildings to have
glass windows. Stained glass windows reached their peak as the Middle Ages drew
to a close, with an increasing number of public buildings, inns and the homes of the
wealthy fitted with clear or coloured glass decorated with historical scenes and coats
of arms.
Venice
In the Middle Ages, the Italian city of Venice assumed its role as the glassmaking centre
of the western world. The Venetian merchant fleet ruled the Mediterranean waves and
helped supply Venice's glass craftsmen with the technical know-how of their counterparts
in Syria, and with the artistic influence of Islam. The importance of the glass industry
in Venice can be seen not only in the number of craftsmen at work there (more than 8,000
at one point). A 1271 ordinance, a type of glass sector statute, laid down certain
protectionist measures such as a ban on imports of foreign glass and a ban on foreign
glassmakers who wished to work in Venice: non-Venetian craftsmen were themselves
clearly sufficiently skilled to pose a threat.
Until the end of the 13th century, most glassmaking in Venice took place in the city itself.
However, the frequent fires caused by the furnaces led the city authorities, in 1291,
to order the transfer of glassmaking to the island of Murano. The measure also made it
easier for the city to keep an eye on what was one of its main assets, ensuring that no
glassmaking skills or secrets were exported.
In the 14th century, another important Italian glassmaking industry developed at Altare,
near Genoa. Its importance lies largely in the fact that it was not subject to the strict
statutes of Venice as regards the exporting of glass working skills. Thus, during the 16th
century, craftsmen from Altare helped extend the new styles and techniques of
Italian glass to other parts of Europe, particularly France.
In the second half of the 15th century, the craftsmen of Murano started using quartz sand
and potash made from sea plants to produce particularly pure crystal. By the end of
the 16th century, 3,000 of the island's 7,000 inhabitants were involved in some way in the
glassmaking industry.
Lead Crystal
The development of lead crystal has been attributed to the English glassmaker George
Ravenscroft (1618-1681), who patented his new glass in 1674. He had been
commissioned to find a substitute for the Venetian crystal produced in Murano and
based on pure quartz sand and potash. By using higher proportions of lead oxide instead
of potash, he succeeded in producing a brilliant glass with a high refractive index
which was very well suited for deep cutting and engraving.
Advances from France
In 1688, in France, a new process was developed for the production of plate glass,
principally for use in mirrors, whose optical qualities had, until then, left much to be
desired. The molten glass was poured onto a special table and rolled out flat. After
cooling, the plate glass was ground on large round tables by means of rotating cast iron
discs and increasingly fine abrasive sands, and then polished using felt disks. The
result of this "plate pouring" process was flat glass with good optical transmission
qualities. When coated on one side with a reflective, low melting metal, high-quality
mirrors could be produced.
France also took steps to promote its own glass industry and attract glass experts from
Venice; not an easy move for Venetians keen on exporting their abilities and know-how,
given the history of discouragement of such behaviour (at one point, Venetian glass
craftsmen faced death threats if they disclosed glassmaking secrets or took their skills
abroad). The French court, for its part, placed heavy duties on glass imports and offered
Venetian glassmakers a number of incentives: French nationality after eight years and
total exemption from taxes, to name just two.
From Craft to Industry
It was not until the latter stages of the Industrial Revolution, however, that mechanical
technology for mass production and in-depth scientific research into the relationship
between the composition of glass and its physical qualities began to appear in the
industry.
A key figure and one of the forefathers of modern glass research was the German
scientist Otto Schott (1851-1935), who used scientific methods to study the effects of
numerous chemical elements on the optical and thermal properties of glass. In the
field of optical glass, Schott teamed up with Ernst Abbe (1840-1905), a professor at the
University of Jena and joint owner of the Carl Zeiss firm, to make significant
technological advances.
Another major contributor in the evolution towards mass production was Friedrich
Siemens, who invented the tank furnace. This rapidly replaced the old pot furnace and
allowed the continuous production of far greater quantities of molten glass.
Increasing Automation
Towards the end of the 19th century, the American engineer Michael Owens (1859-1923)
invented an automatic bottle blowing machine which only arrived in Europe after the turn
of the century. Owens was backed financially by E.D.L. Libbey, owner of the Libbey
Glass Co. of Toledo, Ohio. By the year 1920, in the United States, there were around 200
automatic Owens Libbey Suction Blow machines operating. In Europe, smaller, more
versatile machines from companies like O'Neill, Miller and Lynch were also popular.
Added impetus was given to automatic production processes in 1923 with the
development of the gob feeder, which ensured the rapid supply of more consistently sized
gobs in bottle production. Soon afterwards, in 1925, IS (individual section) machines
were developed. Used in conjunction with the gob feeders, IS machines allowed the
simultaneous production of a number of bottles from one piece of equipment. The
gob feeder-IS machine combination remains the basis of most automatic glass container
production today.
Modern Flat Glass Technology
In the production of flat glass (where, as explained earlier, molten glass had previously
been poured onto large tables then rolled flat into "plates", cooled, ground and
polished before being turned over and given the same treatment on the other surface), the
first real innovation came in 1905 when a Belgian named Fourcault managed to
vertically draw a continuous sheet of glass of a consistent width from the tank.
Commercial production of sheet glass using the Fourcault process eventually got under
way in 1914.
Around the end of the First World War, another Belgian engineer Emil Bicheroux
developed a process whereby the molten glass was poured from a pot directly through
two rollers. Like the Fourcault method, this resulted in glass with a more even
thickness, and made grinding and polishing easier and more economical.
An off-shoot of evolution in flat glass production was the strengthening of glass by means
of lamination (inserting a celluloid material layer between two sheets of glass). The
process was invented and developed by the French scientist Edouard Benedictus, who
patented his new safety glass under the name "Triplex" in 1910.
In America, Colburn developed another method for drawing sheet glass. The process was
further improved with the support of the US firm Libbey-Owens and was first used for
commercial production in 1917.
The Pittsburgh process, developed by the American Pennvernon and the Pittsburgh Plate
Glass Company (PPG), combined and enhanced the main features of the Fourcault and
Libbey-Owens processes, and has been in use since 1928.
The float process developed after the Second World War by Britain's Pilkington Brothers
Ltd., and introduced in 1959, combined the brilliant finish of sheet glass with the
optical qualities of plate glass. Molten glass, when poured across the surface of a bath of
molten tin, spreads and flattens before being drawn horizontally in a continuous
ribbon into the annealing lehr.
Conclusion
Although this brief history comes to a close nearly 40 years ago, technological evolution
naturally continues. Not yet ready to be "relegated" to a history of glass are areas such
as computerized control systems, coating techniques, solar control technology and
"smart matter", the integration of micro-electronic and mechanical know-how to create
glass which is able to "react" to external forces.
