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Obsidian, which is formed naturally
from lava, was used to create the earliest glass objects - arrowheads and other sharp tools.
Spinning Glass from a Roman Yarn
In
his Natural History (77 AD), the Roman historian Pliny the Elder wrote
that thousands of years earlier, "A trading ship carrying nitrum (soda)
anchored (off the coast of Asia Minor); its crew went ashore to prepare
their dinner. Finding no stones on the beach with which to prop their
cooking pots over the fire the sailors used lumps of nitrum from their
ship to support their cookware. When these became heated, they combined
with the sand from the beach to form a strange liquid that flowed in
streams; and this, it is said, was the origin of glass."
A
nice tale, but not true. Cuneiform tablets containing glass-making
recipes indicate that glass was probably first manufactured by the
people living in Syria, Babylonia (Iraq) and Mesopotamia (Iran),
sometime around 3,000 BC. They likely discovered the process by
accident.
Druids and Pharaohs:
The Glass Connection
In
its earliest form, glass was made from impure ingredients, resulting in
a green tint. It was primarily decorative. A few thousand years would
pass before glass possessed the clarity and transparency for window
panes. However, as time progressed, several compounds were introduced
to create a range of colors mimicking precious and semi-precious
stones. Some of these colorants were cobalt, copper, silver, chrome,
iron, gold, manganese, nickel, selenium and cadmium. Glass was "core
formed" or "rod formed". Core formed objects were made by molding
molten glass around a removable core or center, usually a combination
of dung and clay mixed with water. In the rod forming technique, beads
and other small items were made by manipulating a glob of molten glass
on a long rod which was thrust into a kiln until the glass was
malleable.
In
the third millennium BC, Phoenician trading vessels carried glass and
glass-making to Egypt where it was used as decoration by the
aristocracy, and as far away as the Celtic cultures of Britain. The
Egyptians used glass beads as trading collateral in their dealings with
other African peoples, who didn't have access to the secrets of
glass-making. The Romans, and other Europeans after them, continued
using glass beads and other objects to trade in exchange for African
valuables.
Mirrors may have originated with the
Egyptians, and were referred to in the Bible.
Rome's Windows Weren't
Built in a Day
The
glass-makers of Ancient Rome produced an early type of flat glass
without a greenish tint, or any other color for that matter. It was
suitable for windows, but they weren't at all like the windows we have
today. They were small, very thick, and opaque rather than transparent.
A certain amount of natural light filtered in but you couldn't see
through the glass. A notable feature of many Roman windows, and windows
for centuries to come, was a bull's-eye pattern in the center. This was
a consequence of the method used to manufacture the first flat glass.
The glass-maker would blow a large bubble of glass, spinning it round
rapidly while the glass was still soft. The result was a glass disc
attached to the blow pipe. The blow pipe was removed, and the disc was
annealed (the process of cooling glass), then cut into small panes.
There was a bull's-eye on the pane where the blowpipe had been attached.
Crude flat glass was used by the Romans,
ideal for keeping in
warmth in
the colder climates.
Shedding Light On the
Dark Ages
Despite
the murky reputation of the bleak centuries following the decline of
the Roman Empire, glass got lighter. During the Dark Ages, better raw
materials were used and more efficient furnaces were built. Ash from
plants and trees created a superior flux (material that enables glass
to melt at a lower temperature). This ash contained large amounts of
potassium oxide, rather than sodium oxide which was previously used.
Wood fuel for furnaces meant that glassworks were usually situated in
forest areas away from towns. Meanwhile, across Asia in the Far East,
the Chinese started to make glass objects in the 5th century AD.
The Glass Enlightenment
 In
1000 AD, the Egyptian city of Alexandria was considered the preeminent
center for glass-making, but northward in Europe, the miraculous art of
stained glass was evolving. In the 12th century, gorgeous,
multi-colored windows started gracing churches and cathedrals across
the continent, with the finest-Chartres and Canterbury cathedrals, for
example-produced in the 13th and 14th centuries. Most of the flat glass
for religious stained windows was made in France.
The
11th century AD also saw the advent of the first magnifying glass,
which was used by medieval monks as they pored over their calligraphic
manuscripts. The first eyeglasses further reduced squinting in the late
13th century. In 1291, on the Italian island of Murano near Venice, a
transparent glass called cristallo was developed, and crystal glassware
soon became popular throughout Europe. From the 1400s to the 1700s, the
Venetians dominated ornamental glass production.
The first magnifying glass in the 11th
century eventually led to development of the microsocope and telescope.
Revolutionary Glass
In
England, deforestation was a problem as early as the 15th century.
After 1615, glass-makers were required to use coal instead of wood in
their furnaces. In the late 17th century, the English discovered that
adding lead oxide to the glass process resulted in a substance which
was solid, heavy and durable. Also at this time, the French perfected
grinding and polishing techniques and produced the first plate glass,
but only the rich could afford it.
Then,
in the 1700s, there was a political revolution in France and the start
of an industrial revolution in England: and a revolution in glass
production. Compressed air technology created flatter, better glass
panes. Cooling air was blown into a large glass cylinder in controlled
amounts. This cylinder was then slit lengthwise. It was reheated and
allowed to flatten under its own weight. Large, relatively inexpensive
lites (panes) of glass became available and by 1860 flat glass prices
had dropped, making glass affordable in all building construction.
In
the 1820s, a hand-operated machine ended the age of blowing individual
bottles, glasses and flasks. In the 1870s, the first semi-automatic
bottle machines appeared. Plate glass production expanded as water
power, then steam, and then electricity made grinding and polishing
faster and easier. By the 1860s, stores and office buildings were
outfitted with plate glass. The latter part of the 19th century saw the
center of plate glass production move from France and Belgium to the
US. At this time, machinery that rolled glass speeded up the
manufacturing process. The glass was pushed through two rollers and
emerged as a flat sheet onto a steel table. The glass sheets annealed
(cooled) slowly on layers of shelves, then were cut. The first wired
glass was made in the 1890s.
With the French Revolution came a revolution
in glass, with better flat panels possible due to compressed air technology.
A Bright New Century
of
Glass Technology
Transportation,
communication and architecture all benefited from breakthroughs in
glass production throughout the 20th century. Machines were developed
that produced endless sheets of flat glass for windows (window) glass.
New processes strengthened glass by thermal and chemical tempering.
Tints were applied to glass to reduce heat transmission and glare, and
glass coated with metal oxide films reflected heat or conducted
electricity.
But
it is probably the car that motivated the most important changes.
Before 1919, windshields were made of ordinary plate glass and were
therefore highly dangerous when broken. The auto magnate Henry Ford
created the new process of glass lamination, and laminated windshields
became mandatory. The cellulose has since been replaced with polyvinyl
butyral (PVB). In the 1950s, side and rear windows were replaced by
tempered glass, which breaks into small pebble-like pieces when broken.
Fibre-optics and the first photo-sensitive glass came into being in the
1940s. In 1959, float glass replaced flat glass as a preferred material
for residential and commercial windows. The most exciting recent
development is Low-E glass, with a low-emission coating that improves
the energy efficiency of windows.
Mirrored
coatings on today's glass office towers offer much more than just
looks. They help save energy by keeping the climate outside.
A Window On the Future
of Glass
About
75% of the injuries incurred at the 1995 Oklahoma City bombing were
caused by flying glass. Glass manufacturers are united in their efforts
to research and blast-test advanced, heat-hardened and chemically
laminated glass. In Japan, engineers are hard at work on a personal
digital assistant that will be a small sheet of glass you can hold in
your hand. It is expected that soon new anchor systems, cheaper,
thinner laminates, and novel blast-resistant curtain walls will be
available on the commercial market. As with our ancestors, glass
continues to benefit the quality of human life.
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