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Bronze
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History of Bronze
Bronze
was developed about 3500 BC by the ancient Sumerians in
the Tigris-Euphrates Valley. Historians are unsure how this alloy was discovered, but believe that
bronze may have first been made accidentally when rocks
rich in ores of copper and tin were used to build campfire
rings (enclosures for preventing fires from spreading).
As fire heated these stones, the metals may have mixed,
forming bronze. This theory is supported by the fact that
bronze was not developed in North
America, where natural tin and copper ores are rarely found
in the same rocks.
Around
3000 BC, bronze-making spread to Persia, where bronze objects such as ornaments, weapons,
and chariot fittings have been found. Bronzes appeared in
both Egypt and China around 2000 BC. The earliest bronze castings (objects
made by pouring liquid metal into molds) were made in sand;
later, clay and stone molds were used. Zinc, lead, and silver
were added to bronze alloys by Greek and Roman metalworkers
for use in tools, weapons, coins, and art objects.
During
the Renaissance, a series of cultural movements that occurred
in Europe in the 14th, 15th, and 16th centuries, bronze was used to make guns,
and artists such as Michelangelo and Benvenuto
Cellini used bronze for sculpting. The most accurate and
most commonly used method of bronze casting is the lost-wax
method.
Today,
bronze is used for making products ranging from household
items such as doorknobs, drawer handles, and clocks to industrial
products such as engine parts, bearings, and wire. Bronze
is made by heating and mixing the molten metal constituents.
When the molten mixture is poured into a mold and begins
to harden, the bronze expands and fills the entire mold.
Once the bronze has cooled, it shrinks slightly and can
easily be removed from the mold.
Bronze
is a metal compound containing copper and other elements.
The term bronze was originally applied to an alloy of copper
containing tin, but the term is now used to describe a variety
of copper-rich material, including aluminum bronze, manganese
bronze, and silicon bronze.
Bronze
is stronger and harder than any other common alloy except
steel. It does not easily break under stress, is corrosion
resistant, and is easy to form into finished shapes by molding,
casting, or machining.
The
strongest bronze alloys contain tin and a small amount of
lead. Tin, silicon (see end of this article for specifics
on silicon), or aluminum is often added to bronze to improve
its resistance. ilicon bronze
alloys is used today in art castings. As bronze weathers,
a brown or green film forms on the surface. This film inhibits
corrosion. For example, many bronze statues erected hundreds
of years ago show little sign of corrosion. Bronzes have
a low melting point, a characteristic that makes them useful
for brazing—that is, for joining two pieces of metal. When
used as brazing material, bronze is heated above 430°C (800°F),
but not above the melting point of the metals being joined.
The molten bronze fuses to the other metals, forming a solid
joint after cooling.
Lead
is often added to make bronze easier to machine. Silicon
bronze is machined into piston rings and screening, and
because of its resistance to chemical corrosion it is also
used to make chemical containers and in the the
making of bronze art. Manganese bronze is used for valve
stems and welding rods. Aluminum bronzes are used in engine
parts and in marine hardware.
Bronze
containing 10 percent or more tin is most often rolled or
drawn into wires, sheets, and pipes. Tin bronze, in a powdered
form, is sintered (heated without being melted), pressed
into a solid mass, saturated with oil, and used to make
self-lubricating bearings.
In
metallurgy bronze is an alloy of copper, tin, zinc, phosphorus,
and sometimes small amounts of other elements. Bronzes are
harder than brasses. Most are produced by melting the copper
and adding the desired amounts of tin, zinc, and other substances.
The properties of the alloy depend on the proportions of
its components.
Bronze
is used for coins, medals, steam fittings, and gunmetal
and was formerly employed for cannon. Because of its particularly
echoing quality, bell metal, containing from 20% to 24%
tin, is used for casting bells.
Essentially,
to produce a bronze casting, the alloy is heated to at least
1,700 degrees F. at which it melts, and then poured into
some type of fireproof mold of the original work.
Bronze
is of exceptional historical interest and still finds wide
applications. The proportions of copper and tin varied widely
(from 67 to 95 percent in surviving artifacts), but, by
the Middle Ages in Europe, certain proportions were known to yield specific
properties. An alloy described in an 11th-century Greek
manuscript in the library of St. Mark's, Venice,
cites a proportion of one pound copper to two ounces of
tin (8 to 1), approximately that used for bronze gunmetal
in later times. Some modern bronzes contain no tin at all,
substituting other metals such as aluminum, manganese, and
even zinc
Bronze
is harder than copper as a result of alloying that metal
with tin or other metals. Bronze is also more fusible (i.e.,
more readily melted) and is hence easier to cast. It is
also harder than pure iron and far more resistant to corrosion.
The substitution of iron for bronze in tools and weapons
from about 1000bc was the result of iron's abundance compared to copper
and tin rather than any inherent advantages of iron.
Bronze in the Ancient World
In
both Europe and the Middle East, bronze was mainly used
for weapons and cutting tools—swords, spears, arrowheads,
shields, adzes, and axes—although bowls and cauldrons were
also made from bronze. During the 1st millennium, bronze
was especially prized in Greece and later in Rome for sumptuous and elegant furnishings, such as tripods,
bed and table frames, small oil lamps, and tall lampstands,
often elaborately decorated with raised animal or leaf decoration.
Chinese Bronzes
In
China bronze appears to have been used almost exclusively
for bells, mirrors, and vessels in a variety of prescribed
forms for distinct functions in religious rites, as well
as for weapons and for the decoration of horse trappings
and chariots. This first Bronze Age in China lasted from about 1800 to the end of the Qin dynasty (221-206BC. The
bronze ritual vessels are especially admired for the nobility
of their forms and the vigor of their abstract linear decoration.
The decoration consists of highly conventionalized and attenuated
masks and mythical monster forms, such as dragons. These
vessels were cast from molds prepared with the decoration
cut and incised on the inner face, resulting in equivalent
projections on the cast vessel.>
European Bronzes
After
bronze was superseded by iron for weapons, it remained in
use in Europe as an artist's medium. Greek bronze statues, vases, and wine vessels,
sometimes of large size and elaborately gilded, were greatly
admired in Rome. The wandering tribes who gradually superseded Roman
power in Europe (including Italy), also appreciated bronze,
but used it more often for portable items such as shields
and bowls as well as for buckles and brooches (often inlaid
with colored stones or opaque enamel). In church furnishings,
bronze continued to be used for larger pieces, such as candlesticks,
baptismal fonts, and coffers. Perhaps the most famous bronze
sculptures of the Renaissance are Lorenzo Ghiberti's
sumptuously ornamental gilded bronze doors—the Gates of
Paradise (1425-1452)—for the Baptistery at Florence, consisting of ten self-contained rectangular panels
of biblical scenes cast in high relief. Many other Renaissance
artists used this medium for smaller cast figure sculptures,
often inspired by antique works of the classical era; this
prime use for bronze has persisted to the present day.
In
the 18th and 19th centuries, and especially in France, gilt bronze attachments—called ormolu—in the form
of projecting and richly decorated cast mounts on edgings,
drawers, and feet, were added to luxury furniture.
African Bronzes
In
Nigeria, between the 14th and 16th centuries, cast bronze
sculptures of extreme refinement were made at Benin in a highly developed artistic convention unrelated
to European styles.
Silicon Bronze
Silicon,
symbol Si, semimetallic element that
is the second most common element on earth, after oxygen.
The atomic number of silicon is 14. Silicon is in group
14 (or IVa) of the periodic
table. It was first isolated from its compounds in 1823
by the Swedish chemist Baron Jons
Jakob Berzelius.
Silicon
is prepared as a brown amorphous powder or as gray-black
crystals. It is obtained by heating silica, or silicon dioxide
(SiO2), with a reducing agent,
such as carbon or magnesium, in an electric furnace. Crystalline
silicon has a hardness of 7, compared to 5 to 7 for glass. Silicon melts at about 1410° C (about 2570° F), boils at
about 2355° C (about 4271° F), and has a specific gravity
of 2.33.
Silicon
constitutes about 28 percent of the earth's crust. It does
not occur in the free, elemental state, but is found in
the form of silicon dioxide and in the form of complex silicates.
Silicon-containing minerals constitute nearly 40 percent
of all common minerals, including more than 90 percent of
igneous-rock-forming minerals. The mineral quartz, varieties
of quartz (such as chrysoprase,
onyx, flint, and jasper), and the minerals cristobalite
and tridymite are the naturally
occurring crystal forms of silica. Silicon dioxide is the
principal constituent of sand. The silicates (such as the
complex aluminum, calcium, and magnesium silicates) are
the chief constituents of clays, soils, and rocks in the
form of feldspars, amphiboles, micas, and zeolites,
and of semiprecious stones, such as garnet, zircon, topaz,
and tourmaline .
Silicon
is used in the steel industry as a constituent of silicon-steel
alloys. Silicon steel, which contains from 2.5 to 4 percent
silicon, is used in making the cores of electrical transformers
because the alloy exhibits low magnetism. Silicon is also
used as an alloy in copper, brass, and bronze.
Properties
With
the exception of steel, bronze is superior to iron in nearly
every application. Although bronze develops a patina, it
does not oxidize beyond the surface. It is considerably
less brittle than iron and has a lower casting temperature.
Copper-based
alloys have lower melting points than steel and are more
readily produced from their constituent metals. They are
generally about 10 percent heavier than steel, although
alloys using aluminum or silicon may be slightly less dense.
Bronzes are softer and weaker than steel, bronze springs
are less stiff (and so store less energy) for the same bulk.
It resists corrosion (especially seawater corrosion) and
metal fatigue better than steel and also conducts heat and
electricity better than most steels. The cost of copper-base
alloys is generally higher than that of steels but lower
than that of nickel-base alloys.
Copper
and its alloys have a huge variety of uses that reflect
their versatile physical, mechanical, and chemical properties.
Some common examples are the high electrical conductivity
of pure copper, the excellent deep-drawing qualities of
cartridge case brass, the low-friction properties of bearing
bronze, the resonant qualities of bell bronze, and the resistance
to corrosion by sea water of several bronze alloys.
In
the twentieth century, silicon was introduced as the primary
alloying element, creating an alloy with wide application
in industry and the major form used in contemporary statuary.
Aluminum is also used for the structural metal aluminum
bronze.
Bronze
is the most popular metal for top-quality bells and cymbals,
and more recently, saxophones. It is also widely used for
cast metal sculpture (see bronze sculpture). Common bronze
alloys often have the unusual and very desirable property
of expanding slightly just before they set, thus filling
in the finest details of a mould. Bronze parts are tough
and typically used for bearings, clips, electrical connectors
and springs.
Bronze
also has very little metal-on-metal friction, which made
it invaluable for the building of cannons where iron cannonballs
would otherwise stick in the barrel. It is still widely
used today for springs, bearings, bushings, automobile transmission
pilot bearings, and similar fittings, and is particularly
common in the bearings of small electric motors. Phosphor
bronze is particularly suited to precision-grade bearings
and springs.
Bronze
is typically 60% copper and 40% tin. Alpha bronze consists
of the alpha solid solution of tin in copper. Alpha bronze
alloys of 4–5% tin are used to make coins, springs, turbines
and blades.
Commercial
bronze (otherwise known as brass) is 90% copper and 10%
zinc, and contains no tin. It is stronger than copper and
it has equivalent ductility. It is used for screws and wires.
Another
useful property of bronze is that it is non-sparking. That
is, when struck against a hard surface, unlike steel, it
will not generate sparks. This is used to advantage to make
hammers, mallets, wrenches and other durable tools to be
used in explosive atmospheres or in the presence of flammable
vapors.
Bronze Age
The
Bronze Age was a period in the civilization's development
when the most advanced metalworking (at least in systematic
and widespread use) consisted of techniques for smelting
copper and tin from naturally occurring outcroppings of
ore, and then alloying those metals in order to cast bronze.
The Bronze Age forms part of the three-age system for prehistoric
societies. In that system, it follows the Neolithic in some
areas of the world. In many parts of sub-Saharan Africa, the Neolithic is directly followed by the Iron Age.
Origins
The
place and time of the invention of bronze are controversial,
and it is possible that bronzing was invented independently
in multiple places. The earliest known tin bronzes are from
what is now Iran and Iraq and date to the late 4th millennium BC, but there are claims of an earlier
appearance of tin bronze in Thailand in the 5th millennium BC. Arsenical bronzes were
made in Anatolia and on both sides of the Caucasus by the early 3rd millennium BC. Some scholars date some arsenical bronze
artefacts of the Maykop
culture in the North
Caucasus
as far back as the mid 4th millennium BC, which would make
them the oldest known bronzes, but others date the same
Maykop artefacts
to the mid 3rd millennium BC .
Ancinet Near East
The
Bronze Age in the Near East is divided into three main periods (the dates are
very approximate):
* EBA - Early
Bronze Age (c.3500-2000 BC)
* MBA - Middle Bronze Age (c.2000-1600 BC)
* LBA - Late Bronze
Age (c.1600-1200 BC)
Each
main period can be divided into shorter subcategories such
as EB I, EB II, MB IIa etc.
Metallurgy
developed first in Anatolia, modern Turkey. The mountains in the Anatolian highland possessed
rich deposits of copper and tin. Copper was also mined in
Cyprus, Egypt, the Negev desert, Iran and around the Persian Gulf. Copper was usually mixed with arsenic, yet the growing
demand for tin resulted in the establishment of distant
trade routes in and out of Anatolia. The precious copper was also imported by sea routes
to the great kingdoms of Ancient Egypt and Mesopotamia .
The
Early Bronze Age saw the rise of urbanization into organized
city states and the invention of writing (the Uruk
period in the fifth millennium BC). In the Middle Bronze
Age movements of people partially changed the political
pattern of the Near
East (Amorites, Hittites, Hurrians,
Hyksos and possibly the Israelites).
The Late Bronze Age is characterized by competing powerful
kingdoms and their vassal states (Ancient Egypt, Assyria, Babylonia, Hittites, Mitanni). Extensive contacts were made with the Aegean civilization (Ahhiyawa, Alashiya)
in which the copper trade played an important role. This
period ended in a widespread collapse which affected much
of the Eastern Mediterranean and Middle East.
Iron
began to be worked already in Late Bronze Age Anatolia.
The transition into the Iron Age c.1200 BC was more of a
political change in the Near East rather
than of new developments in metalworking.
Indian Bronze Age
The
Bronze Age on the Indian subcontinent began around 3300
BC with the beginning of the Indus Valley civilization. Inhabitants of the ancient Indus Valley, the Harappans, developed new techniques
in metallurgy and produced copper, bronze, lead and tin.
East Asia
Bronze
artifacts were exhumed in historic site of Majiayao
culture (3100 BC to 2700 BC) of China. However, it is commonly accepted that China's Bronze Age began from around 2100 BC during the
Xia dynasty.
The
Erlitou culture, Shang
Dynasty and Sanxingdui culture
of early China used bronze vessels for rituals as well as farming implements and weapons
Southeast
Asia
In
Ban Chiang, Thailand, (Southeast
Asia)
bronze artifacts have been discovered dating to 2100 BC
.
Korean
peninsula
The
Middle Mumun pottery period culture of the southern Korean Peninsula gradually adopted bronze production (circa 700-600? BC) after a period
when Liaoning-style bronze daggers
and other bronze artifacts were exchanged as far as the
interior part of the Southern Peninsula (circa 900-700 BC). The bronze daggers lent prestige
and authority to the personages who wielded and were buried
with them in high-status megalithic burials at south-coastal
centres such as the Igeum-dong
site. Bronze was an important element in ceremonies and
as for mortuary offerings until AD 100.
Aegean
The
Aegean Bronze Age civilizations established a far-ranging
trade network. This network imported tin and charcoal to
Cyprus, where copper was mined and alloyed with the tin
to produce bronze. Bronze objects were then exported far
and wide, and supported the trade. Isotopic analysis of
the tin in some Mediterranean bronze objects indicates it
came from as far away as Great Britain.
Knowledge
of navigation was well developed at this time, and reached
a peak of skill not exceeded until a method was discovered
(or perhaps rediscovered) to determine longitude around
1750 AD, with the notable exception of the Polynesian sailors.
The
Minoan civilization based from Knossos appears to have coordinated and defended its Bronze
Age trade.
One
crucial lack in this period was that modern methods of accounting
were not available. Numerous authorities[citation needed]
believe that ancient empires were prone to misvalue staples in favor of luxuries, and thereby perish
by famines created by uneconomic trading.
How
the Bronze Age ended in this region is still being studied.
There is evidence that Mycenaean administration of the regional
trade empire followed the decline of Minoan primacy. Evidence
also exists that supports the assumption that several Minoan
client states lost large portions of their respective populations
to extreme famines and/or pestilence, which in turn would
indicate that the trade network may have failed at some
point, preventing the trade that would have previously relieved
such famines and prevented some forms of illness (by nutrition).
It is also known that the breadbasket of the Minoan empire,
the area north of the Black Sea, also suddenly lost significant
portions of its population, and thus probably some degree
of cultivation in this era.
Recent
research has discredited the theory that exhaustion of the
Cypriot forests caused the end of the bronze trade. The
Cypriot forests are known to have existed into later times,
and experiments have shown that charcoal production on the
scale necessary for the bronze production of the late Bronze
Age would have exhausted them in less than fifty years.
One
theory says that as iron tools became more common, the main
justification of the tin trade ended, and that trade network
ceased to function as it once did. The individual colonies
of the Minoan empire then suffered drought, famine, war,
or some combination of these three factors, and thus they
had no access to the far-flung resources of an empire by
which they could easily recover.
Another
family of theories looks to Knossos itself. The Thera eruption
occurred at this time, 40 miles north of Crete. Some authorities speculate that a tsunami from Thera
destroyed Cretan cities. Others say that perhaps a tsunami
destroyed the Cretan navy in its home harbor, which then
lost crucial naval battles; so that in the LMIB/LMII event (c. 1450 BC) the cities of Crete burned and the Mycenaean civilization took over Knossos. If the eruption occurred in the late 17th century
BC (as most chronologists now think), then its immediate
effects belong to the Middle Bronze to Late Bronze Age transition,
and not to the end of the Late Bronze Age; but it could
have triggered the instability which led to the collapse
first of Knossos and then of Bronze Age society overall.
One such theory looks to the role of Cretan expertise in
administering the empire, post-Thera. If this expertise was concentrated in Crete, then the Mycenaeans may have made crucial
political and commercial mistakes when administering the
Cretans' empire.
More
recent archaeological findings, including on the island of Thera (more commonly known today as Santorini),
suggest that the center of Minoan Civilization at the time
of the eruption was actually on this island rather than
on Crete. Some think that this was the fabled Atlantis (a map drawn on a wall
of a Minoan palace in Crete depicts an island similar to that described by Plato
and similar too to the form Thera
very likely had prior to its explosion). According to this
theory, the catastrophic loss of the political, administrative
and economic center by the eruption as well as the damage
wrought by the tsunami to the coastal towns and villages
of Crete precipitated the decline of the Minoans. A weakened political entity
with a reduced economic and military capability and fabled
riches would have then been more vulnerable to human predators.
Each
of these theories is persuasive, and aspects of all of them
may have some validity in describing the end of the Bronze
Age in this region.
Europe
Central Europe
Bronze Age weaponry and ornaments
In
Central Europe, the early Bronze Age Unetice
culture (1800-1600 BC) includes numerous smaller groups
like the Straubingen, Adlerberg and Hatvan cultures. Some very rich burials, such as the one
located at Leubingen with grave
gifts crafted from gold, point to an increase of social
stratification already present in the Unetice culture. All in all, cemeteries of this period are
rare and of small size. The Unetice
culture is followed by the middle Bronze Age (1600-1200
BC) Tumulus culture, which is characterised by inhumation burials in tumuli (barrows).
In the eastern Hungarian Körös
tributaries, the early Bronze Age first saw the introduction
of the Mako culture, followed
by the Ottomany and Gyulavarsand cultures.
The
late Bronze Age urnfield culture, (1300 BC-700 BC) is characterized by cremation
burials. It includes the Lusatian
culture in eastern Germany and Poland ((1300-500 BC) that continues into the Iron Age.
The Central European Bronze Age is followed by the Iron
Age Hallstatt culture (700-450
BC).
Important sites include:
* Biskupin (Poland)
* Nebra (Germany)
* Zug-Sumpf, Zug, Switzerland
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Northern Europe
In northern
Germany, Denmark, Sweden and Norway, Bronze Age inhabitants manufactured many distinctive
and beautiful artifacts, such as the pairs of lurer
horns discovered in Denmark. Some linguists believe that a proto-Indo-European
language was probably introduced to the area around 2000 BC, which
eventually became the ancestor of the Germanic languages. This would
fit with the evolution of the Nordic Bronze Age into the most probably
Germanic pre-Roman Iron Age.
The age is
divided into the periods I-VI according to Oscar Montelius.
Period Montelius V already belongs to
the Iron Age in other regions.
British
Isles
In Great Britain, the Bronze Age is considered to have been the period
from around 2100 to 700 BC. Immigration brought new people to the
islands from the continent. Recent tooth enamel isotope research
on bodies found in early Bronze Age graves around Stonehenge indicate that at least some of the immigrants came
from the area of modern Switzerland. The Beaker people displayed different behaviours from the earlier Neolithic people and cultural
change was significant. Integration is thought to have been peaceful
as many of the early henge sites were
seemingly adopted by the newcomers. The rich Wessex culture developed in southern Britain at this time. Additionally, the climate was deteriorating,
where once the weather was warm and dry it became much wetter as
the Bronze Age continued, forcing the population away from easily-defended
sites in the hills and into the fertile valleys. Large livestock
ranches developed in the lowlands which appear to have contributed
to economic growth and inspired increasing forest clearances. The
Deverel-Rimbury culture began to emerge
in the second half of the 'Middle Bronze Age' (c. 1400-1100 BC)
to exploit these conditions. Cornwall was a major source of tin for much of western Europe
and copper was extracted from sites such as the Great Orme mine in northern Wales. Social groups appear to have been tribal but with
growing complexity and hierarchies becoming apparent.
Also, the burial
of dead (which until this period had usually been communal) became
more individual. For example, whereas in the Neolithic a large chambered
cairn or long barrow was used to house the dead, the 'Early Bronze
Age' saw people buried in individual barrows (also commonly known
and marked on modern British Ordnance Survey maps as Tumuli), or
sometimes in cists covered with cairns.
The greatest
quantities of bronze objects found in England were discovered in East Cambridgeshire, where the most important finds were recovered in
Isleham (more than 6500 pieces).[1]
Bronze Age boats
* Ferriby Boats
* Langdon Bay
hoard - see also Dover Museum
* Divers unearth Bronze Age hoard off the
coast of Devon
* Moor Sands finds, including a remarkably
well preserved and complete sword which has parallels with material
from the Seine basin of northern France
Ireland
The Bronze
Age in Ireland commenced in the centuries around 2000 BC when copper
was alloyed with tin and used to manufacture Ballybeg
type flat axes and associated metalwork. The preceding period is
known as the Copper Age and is charcaterised
by the production of flat axes, daggers, halberds and awls in copper.
The period is divided into three phases Early Bronze Age 2000-1500
BC; Middle Bronze Age 1500-1200 BC and Late Bronze Age 1200-c.500
BC. Ireland, is also known for a relatively large number of Early
Bronze Age Burials.
The Early Bronze
Age: one of the characteristic artifact types of the Cooper/Bronze
Age in Ireland is the flat axe. There are 5 main types of flat axes,
Lough Ravel c.2200 BC Ballybeg
c.2000 BC, Killaha c.2000 BC, Ballyvalley
c. 2000-1600 BC, Derryniggin c. 1600
BC and a number of metal ingots in the shape of axes.
Americans
Andean Bronze Age
An Andean bronze
bottle made by Chimú artisans from circa
AD 1300.
The Bronze
Age in the Andes region of South
America is
thought to have begun at about 900 BC when Chavin
artisans discovered how to alloy copper with tin. The first objects
produced were mostly utilitarian in nature, such as axes, knives,
and agricultural implements. Later on, however, as the Chavin
became more experienced in bronze-working technology they produced
many ornate and highly decorative objects for administrative, religious,
and other ceremonial purposes, as well as household use, as decorative
work in gold, silver and copper was a highly developed tradition
that had already long been known to the Chavin.
Americans
Andean Bronze Age
An Andean bronze
bottle made by Chimú artisans from circa
AD 1300.
The Bronze
Age in the Andes region of South
America is
thought to have begun at about 900 BC when Chavin
artisans discovered how to alloy copper with tin. The first objects
produced were mostly utilitarian in nature, such as axes, knives,
and agricultural implements. Later on, however, as the Chavin
became more experienced in bronze-working technology they produced
many ornate and highly decorative objects for administrative, religious,
and other ceremonial purposes, as well as household use, as decorative
work in gold, silver and copper was a highly developed tradition
that had already long been known to the Chavin.
From stone to copper:
Although the
Funnelbeaker culture introduced copper to northern Europe it took until after its decline before the use of copper became more
wide-spread in this area, therefor the
transfer period between the Stone Age and the Bronze Age is often
called the "Copper Age".
In the period
after the Funnelbeaker culture a new culture was introduced to Europe
that covered an enormous area from the lands west of the Rhine to
the east of the Wolga, this culture
is called the "Corded Ware culture complex" (German: Schnurkeramik,
Dutch: Snoerceramiek, Swedish: Snörkeramik),
the origins of the Corded Ware culture are debated but one of the
most plausible theories says that it was a mixture of the native
culture of an area and one or more foreign cultures that were introduced
by invaders from the east, it is widely believed that the Corded
Ware culture was the first Indo-European culture in Europe but this
can not be said with certainty because not enough is known from
this period to draw any conclusions yet.
Another culture
that played an important role during this period of foreign influences
was the Bellbeaker culture that outlived the Corded Ware culture
and consisted of many small culture groups scattered over a large
area.
The Corded Ware culture
The Corded
Ware culture existed from 2900BC to
about 2450/2350BC and can be divided
into three groups; the Eastern European group, the Central European
group, and the Northern European group (that was also known as Single
Grave culture (English), Einzelgrabkultur
(German), Enkelgrafcultuur (Dutch), or Enkelgravkultur
(Swedish)).
This cultures
were named after their pottery
that was decorated with thin shaded lines that looked like cords,
they also used copper axes but the main characteristic of the Corded
Ware culture were the stone battle-axes they used, this axes had
a hole in the middle that was fitted on a handle and was then secured
with a cord, they had a sharp side and a blunt side that made it
look like a combination of an axe and a hammer, because of this
axes the Corded Ware culture is also known as the "Battle-axe
culture".
The Corded
Ware culture also introduced horseriding
in many places, the horsebreed they used for this was the Tarpan;
a small type of horse that was native to Europe, unfortunately it
became extinct in 1876 but during the Bronze Age there were many
herds of wild Tarpans that were domesticated and used by the first European
horsemen.
The dead were
buried in rectangular pits, in most cases a round mound was built
on top of the grave and men and women were buried in opposite directions,
perhaps this had some religious meaning, men were often given a
battle-axe as gravegift though near
the end of the Corded Ware culture the axe was replaced by the dagger
as the most common male gravegift, perhaps
this reflects a shift from the battle-axe to the dagger as the most
used weapon.
In a bog near
Wiepenkathen in Germany a flint dagger from 2400BC has been found that either dates from the late Single
Grave culture (Northern European group of the Corded Ware culture)
or the Bellbeaker culture, the dagger
was left in the bog as an offering and its grip and sheath were
decorated with a herringbone pattern, some daggers from that period
also had a grip in the form of a fishtail.
The Bellbeaker culture
The Bellbeaker
culture (German: Glockenbecherkultur,
Dutch: Klokbekercultuur) is named after the bell-shaped beakers
it produced, this culture existed from around 2900BC
to 1800/1700BC and coexisted with both
the Corded Ware culture and the cultures after it until the start
of the Bronze Age.
The Bellbeaker
culture was not a united culture in a single area but rather a group
of small related cultural groups that were scattered over Europe;
groups belonging to the Bellbeaker culture
have been found in Morocco, Spain, France, Italy, the British islands
(perhaps the legendary Milesians from Celtic mythology reflect an invasion of Bellbeaker people?), parts of the Netherlands and Germany,
northern Denmark, the Alps, and even parts of eastern Europe; perhaps
the Bellbeaker culture consisted of semi-nomadic tribes who
migrated through Europe and eventually settled when they reached
a place they liked.
The amount
of Bellbeaker groups in northern Europe was rather small but
their culture did leave its mark in many places, the Bellbeaker
influence was was especially high in
the eastern parts of England and Scotland, Belgium, the Netherlands
(excluding the northeast), Denmark (mainly the northern tip of Jutland),
and in Germany (along the Rhine and the Danube, the mouth of the
Oder, the source of the Elbe, and the
Harz area).
The origin
of the Bellbeaker culture is debated but it is believed to originate
from the Iberian
peninsula (modern
day Spain and Portugal), perhaps later combined with cultural influences
from Central
Europe.
In most cases
a migration of culture is caused by the transfer of ideas rather
than a migration of people but this was not entirely true for the
Bellbeaker culture; in parts of Denmark
and the Netherlands burial places have been found that contained
both skeletons of tall long-skulled people (the native Nordic people)
and small short-skulled people (who are believed to be the early
Bellbeaker settlers), it seems that the immigrants coexisted
with the local population who adopted parts of their culture and
the use of (among other things) bellbeakers,
the short-skulled skeletons are not found in graves from later periods
and it is believed that the local population either dislodged or
assimilated the Bellbeaker people, there is also evidence of another immigration
of Nordic settlers from Scandinavia and other areas, but despite
this the cultural influences of the Bellbeaker
people remained for quite some time.
The Bellbeaker
culture mainly buried their dead though some rare examples of cremation
are known too, they are also believed to have had a special warrior-class
and some male burials contained daggers made of flint, copper, or
even bronze, many men also carried a rectangular bone or stone plate
tied around their left arm that was probably used by archers as
wrist protection against the recoil of a bow string.
Just like the
Corded Ware culture the Bellbeaker culture
also introduced horseriding in many places, combined with their large area
of settlement they were probably a very mobile people.
The transfer period
After the decline
of the Corded Ware culture northern Europe was dominated by two cultures: the Aunjetitz culture and the Nordic circle, though the Bellbeaker culture also still played a role in this period.
The Aunjetitz culture
The Aunjetitz
culture (also known as Unetice culture)
roughly lived between the rivers Rhine, Danube, and Vistula, it existed from about 2300BC
to 1500BC but this dates are still debated
so there may even be a difference of up to a few centuries.
The Aunjetitz
culture was one of the first cultures in northern Europe that started using bronze on a small scale, it also developed glass
working and imported exotic materials from abroad.
The villages
of the Aunjetitz culture were surrounded with farmland and protected
by palisades, many hill fortressess
were also built in this time which implies that the people often
had to deal with unfriendly neighbours.
The battles
of that time became different too; armies became more mobile because
of the use of horses and chariots, battle axes and archery became
less important and armies started using the spear as their main
weapon, the shield also became a part of a warrior's standard equipment
as well as the dagger, different types of body armour were also introduced and eventually swords were used
too.
The Nordic circle
This cultural
group existed from 1800BC to 1500BC
and consisted of many closely related cultures that inhabited Scandinavia
and the northern parts of the Netherlands and Germany, the name
"Nordic circle" is a translation of the German name "Nordischer
Kreis" that was introduced by the
Swedish historian Oskar Montelius
to describe the many cultural groups that inhabited northern Europe
in that period.
The people
of the Nordic circle lived in small villages that consisted of rectangular
houses with a small entry hall, they conducted amber trade and buried
their dead in mounds.
They mainly
worshipped the sun and there are signs that they considered the
horse to be a holy animal, in battle they also used war chariots
with multiple horses, the Nordic circle
started using bronze around 1500BC .
From copper to bronze
Although copper
was used to make tools it was too soft to be durable and therefor
the people started looking for ways to make it stronger, they added
arsenic to it which made the copper harder and lowered the melting
temperature but it remained too soft, eventually they discovered
that adding a small amount of tin to the copper created an alloy
that was much harder than copper or arsenic-copper, this alloy is
called bronze; to make bronze one first had to obtain tin and copper,
this materials were harvested in the mountains or in deep mines:
Tin was obtained
by mining cassiterite and extracting
the tin from it by burning it with coal in a furnace so that only
the tin remained.
Copper was
found in green- or blue-coloured copper
veins, this veins were first heated with fires after which water
was poured over the heated rock; the copper ore and the surrounding
rock then expanded and contracted in different ways which caused
cracks between those two, wooden wedges were then driven between
this cracks and water was poured over them; the wet wood expanded
and made the cracks even wider after which the copper ore was loose
from the rock and could be collected.
The copper
ore that can be found in Europe is strongly contaminated with sulfur
and iron so before it could be used it had to be purified; the ore
was first roasted in a fire to make the sulfur in it burn up and
what remained was melted in an oven together with charcoal and quartz,
this separated the iron from the copper.
After the melting
process the iron was often thrown away because it was hardly used
for anything (iron use was introduced much later), the copper was
used to make bronze for weapons and jewellry,
for normal every day items the people still used stone.
To make bronze
the copper (90%) and tin (10%) were melted in ovens and mixed together,
this created the alloy known as bronze, to create a bronze object
the bronze had to be melted to at least 950° Celcius
or 1742° Fahrenheit (the melting point of bronze) after which it
was poured into a mould.
A mould was
made of stone or a metal with a higher melting point than bronze,
for unique objects the cire-perdue or "lost wax" method was used in which
the form of the desired object was made of wax and then covered
with clay, it was then heated which hardened the clay and melted
the wax inside, the remaining clay mould was then filled up with
bronze and when it was hard the clay was broken and a bronze object
remained.
The Bronze Age cultures:
The introduction
of bronze resulted in many local bronze cultures, during the Bronze
Age there were so many of this small cultural groups that they are
too numerous to name here and would only make it more confusing
for the reader, therefor I shall only
name the largest and most important cultures, most of the smaller
cultures fell within their sphere of influence:
The Urnfield culture
The Urnfield
culture (German: Urnfeldkultur, Dutch:
Urnveldcultuur) existed from about 1250BC
to 600BC but as usual this dates are
debated, the Urnfield culture originated from Hungary and in 800BC it stretched out from Spain to the Balkans and from
Italy to Central Germany, because of that it was a very heterogenous
culture that was adopted by many peoples throughout Europe.
In the Urnfield
culture the dead were cremated and the ashes was put in urns that
were placed above ground in long rows on hills in a field, hence
the name "urnfield".
The Urnfield
culture was very skilled in bronze working and the people lived
in fortified villages that were often situated near lakes, it was
also a real warrior culture; the Urnfield
armies used chariots, shields, helmets, bronze body armour,
and bronze swords.
In central
Europe the Urnfield culture eventually gave birth
to the Celtic Hallstatt culture though
this two cultures existed side-by-side for some time, the Urnfield
culture is often seen as the Proto-Celtic culture but it also influenced
many other cultures in Europe.
The Hallstatt culture
The Hallstatt
culture was the first Celtic culture and it originated from the
heart of the Urnfield culture, it existed from 800BC
to 450BC and was one of the first cultures
in Europe that started using iron, it is estimated that they started with that
around 750BC.
From the Hallstatt culture the use of iron as well as the Celtic
language and culture was spread over Europe which resulted
in a Celtic hegemony over Europe that would
last until the Roman conquest of Gaul in 52BC.
The Nordic bronze cultures
While most
of Europe was dominated by the Urnfield
culture northern Europe was a patchwork of many small bronze cultures
that were influenced by the Urnfield culture but remained largely independant,
especially around the coasts of the North Sea this people had developed
into skilled seafarers with a large trading network, at the end
of the Bronze Age this cultures started moving south and layed
the foundations of the later Germanic culture.
Just like the
Germans later did the Nordic Bronze Age people carried cloaks made
of fur or wool over their normal clothing (both men and women),
men also carried blouse-like garments and sometimes caps, women
carried long or short skirts that sometimes had beautiful embroideries,
shoes were made from a single piece of
leather.
Jewellry (especially bronze) was also very popular in that
time and the people carried it everywhere; around their upper- and
lower arms, fingers, legs, neck, on their heads, and sometimes even
on their clothing.
During the
beginning of the Bronze Age the dead were still buried in graves
with small mounds built on top but eventually cremation became more
popular and the dead were interred in urns, this may have been an
influence from the Urnfield culture.
Bronze Age religion
Although not
much is known about the religion of the Bronze Age it is still possible
to learn from archeological evidence (offerings, rock carvings,
etc.) and the religion of the succeeding cultures.
It can be said
with certainty that sun worship played an important role in the
religion of the Nordic Bronze Age people and in Trundholm
(Denmark) a beautiful wagon carrying a sundisk
was found with a miniature horse in front of it, which reminds of
the Germanic belief that the sun and the moon were carried across
the sky by horse-pulled chariots.
Besides this
sundisks the people also made golden sunships,
which reflects an alternative belief about the sun being carried
by a ship, such a sunship is believed
to be depicted on the stardisk of Nebra (Germany),
it is also possible that the worship of the Germanic sungod
Balder dates from this time but this is mere speculation of course,
as is the theory that the wargod Tiwaz
was adopted from the Indo-European pantheon during this period.
Rock carvings
from the Bronze Age also show sundisks,
ships, and depictions of what are believed to be gods, some of them
are depicted with a spear (Wodan?) and others carry something that looks like an axe
or a hammer (Thunar?).
Ships were
also important to the Bronze Age people and they are often depicted
on rocks and objects, symbols like the sunwheel
(circle with cross in it) were also used and seem to have been associated
with wagonwheels and the sun.
Just like in
the preceding periods it seems that holy places in nature still
played an important role during the Bronze Age and most of the offerings
in that time were deposited in water, clefts in rocks, on mountains
or hills, and in bogs.
In some bogs
wooden idols were placed that probably served as special offering
places, a practice that is also known from the Germanic period,
perhaps this idols represented a god to whom the bog was dedicated.
Weapons and
other spoils of war were also offered, in most cases the items were
first bended or broken to prevent the offerings from being stolen,
other offerings were jewellry, pottery, wagonparts,
horseriding-gear, agricultural tools, and semi-finished
products.
The most characteristic
offerings of the Nordic Bronze Age are the lyres (wind instruments)
that were mainly found in bogs in Scandinavia, though examples from
Germany are known too, most of them were offered in pairs and they
are believed to have played an important role in religious rituals,
other spectacular offerings are golden dishes and cone-shaped golden
hats that were used throughout Europe in that time, probably by
heathen priests or other important persons.
In a bog near
Metz in Germany a deposit of 70 centimeter (28 inches) long bronze
halberds was found that dates from about 2100-1950BC,
the halberds were not strong enough for practical use so they are
believed to have been used as sceptres by important persons, this type of halberds have
also been found in Scandinavia though they were originally imported
from central Europe.
Something that
dates from a later period (1300-1050BC)
is the bog body that was found in a bog in the Dutch province of Drenthe, the body is named "the man of Emmer-Erfscheidenveen" and it was ritually strangled, it
is the oldest bog body that was found in the Netherlands.
Another interesting
offering is the crown-shaped neckring
that dates from 600BC and was found
in a bog near Emmendorf in Germany,
it was probably worn during religious ceremonies and weighs 770
gram, it must have been an uncomfortable item to wear.
Although most
holy places during the Bronze Age were places in nature there are
also some examples of man-made structures; on the Spandau
lake in the German capital of Berlin there used to be a wooden platform
where weapons (spoils of war?) were offered into the lake for a
long time and in Bargeroosterveld in the Netherlands a temple was found that
was built between 1478BC and 1470BC
(middle Bronze Age), it was made of wooden beams with horn-like
tips pointing upwards, within the structure there were 4 posts on
which a small plateau may have rested that was perhaps used to lay
offerings on, another theory is that it served to lay dead people
on during funeral ceremonies though its location in the bog suggests
that it was an offering place, eventually the little temple was
destroyed, the reason for this is unknown but it may point to a
religious conflict or a ritual offering of the temple by destroying
it .
From bronze to iron
Although bronze
was a good and useful metal there was an even stronger type of metal
whose secrets were reveiled to the people at the end of the Bronze Age; iron,
this metal was called something like "isarna"
by the early Germans, a word that was adopted from Celtic or Proto-Indo-European
and meant something like "strong metal" or "holy
metal".
Iron ore can
be found in iron veins underground and in mountains though it can
also be found in swamps and other places with a wet soil where iron
particles in the water oxidize and form iron depositions, this type
of iron is called limonite or swamp iron and was often used in northern
Europe.
The temperature
needed to melt iron into a liquid state is 1540° Celcius
(2804° Fahrenheit) and to make it soft enough to work with a temperature
of at least 1000° Celcius (1832° Fahrenheit)
is needed, such extreme temperatures can not be reached with wood
so charcoal was needed to make the fire hot enough, a fire in the
open air cools down too quickly so a furnace also had to be built;
a hole was dug in the ground and from mat-plaiting and clay a 1
meter (39 inch) high cone-shaped furnace was built on top of it,
it was then alternately filled with pieces of swamp iron (or iron
ore) and charcoal.
When the furnace
was full everything was set on fire and stirred up with bellows
until it reached a temperature of 1050 - 1150° Celcius
(1922 - 2102° Fahrenheit), this did not melt the iron but transformed
it into a sticky, almost liquid mass of which the iron and the waste
products (also called "slag") were separated.
The slag was
thrown away and the iron had to be heated again and was hammered
to remove further contaminations from it, contaminations make the
iron weak so the more it was heated and hammered the better the
quality became, after that the iron could be used to make weapons
or other objects, this method was used until far in the Middle Ages.
To make steel
a small amount of carbon has to be added to the iron, which makes
it harder but also more brittle, steel was unknown in the Iron Age
but there is evidence that the Vikings made it during the early
Middle Ages.
Stainless steel
was invented much later (in 1913) by the Englishman Harry Brearley
and is made by adding chromium to the steel (minimal 10.5%), a small
amount of nickel is also added, stainless steel is shinier, harder,
but more brittle than normal iron and has a high resistance to corrosion
(rust).
This last two
metals are a bit off-topic but I wanted to mention them anyway to
show what the discovery of iron has led to, just take a look in
your kitchen drawer and imagine we would still use stone and bronze.
The Iron Age
The first indications
for the use of iron in central- and northern Europe date from the
8th century BC but large scale use of iron was introduced to northern
Europe around 500BC by the Germanic Jastorf
culture who probably learned it from the Celtic Hallstatt
culture, therefor the beginning of the
northern European Iron Age as well as the birth of the Germanic
culture are dated to 500BC.
Quanín (bronze)
It is a common
misconception that pre-Colombian Americas lacked bronze and thus were not able to deploy hardened
copper alloys. Copper alloys are reported as ‘guanín’
by Colombus [1]. This misconception
may well arise because tin, the common component of Eurasian bronze
(although common in Bolivia), is rare in the Caribbean basin.
However, copper,
iron, manganese, nickel, chrome, and cobalt and zinc, copper and
manganese mixed into a matrix of iron sulfides and other metal sulfides
gold, cobalt, nickel, etc are readily available, often glittering
in such minerals as pyrite, fools gold, the brassy golden yellow
cubanite, marcasite etc on the surfaces of the common place once submerged
karst rock formations of these islands.
Thus guanín
could well be a manganese bronze. Today US “gold dollars” are made
of a probably similar alloy 88.5 % copper, 6% zinc, 3.5% manganese,
and 2% nickel [2]. However, it should be noted that nickel has a
melting temperature well above that produced by even a bellowed
kiln (and bellows were probably first employed some time after 300
BC in China) so it would be rather unlikely that guanin would have contained nickle.
Thus Columbus’s report of metal axes in lands and seas of the Caribbean although viewed skeptically by some cannot be readily
dismissed [3]. In this cited article these authors attribute this
bronze to the Mayans. One might keep in mind that the Mayans were
in trading contact with the Taínos who
used the word guanín to describe the
copper alloys they used for ornamental and religious purposes, and
in addition there were readily available deposits of the necessary
ores (see above) in the Major Antilles. The existence of pre-colombian
metal tools in the Americas is finally considered "fact" [4], the question
is which ethnicities, nations or civilizations had these objects.
Thus classification of Taíno technological
progress as merely Neolithic may well be an understatement awaiting
archeological resolution of Taíno use
of guanín alloy tools.
Richard Hakluyt (Hakluyt, 1909) reported
(circa 1592) that there were different (non-Taíno,
presumable Carib) names for gold (calcouri),
silver (perota), iron (mointiman)
and copper oxide ores (tacorao) in the
Caribbean island of Trinidad, off the coast of Venezuela.
BRONZE SCULPTURE: THE ART OF
LOST WAX
In the third
millennium B.C., somewhere between the Black
Sea and the
Persian Gulf, an artist crafted a vision in beeswax, covered it
in liquid clay and cooked it in a fire. In the flames the wax was
lost, replaced by empty space. Tin and copper - alloys of bronze
– were gathered and heated. Once melted, the metal was poured into
the cavity of the fire-hardened clay. The metal cooled and the sculptor
knocked the clay from the metal. The first bronze was cast.
Ancient "Lost
Wax" bronze castings have withstood the centuries, visually
telling the tale of past cultures, their religions and their social
structures. For example: Chinese bronzes often depicted
ceremonial imagery, Indian and Egyptian castings frequently represented
deities, the Africans cast images of nature, and the Greeks re-created
the human Form. Many of these
cultures have grown obsolete, religions have evolved and societies
have changed, but an intriguing visual history survives through
the surviving bronze works. Certain elements of the "Lost Wax"
process have indeed been refined, yet today bronze casting remains
essentially the same as it was in 2,000 BC during the Akkadian
period.
Modern sculptors
who want their pieces cast in bronze depend upon a foundry. There, artisans skillfully apply the "Lost
Wax" method to wood, stone, clay, plaster and essentially any
other form of sculpture to transform the artist’s vision into bronze.
THE RUBBER MOLD
The metamorphosis
of a sculpture from the original medium into bronze begins with
a rubber mold. The original sculpture must remain stationary
during the mold making process. To accomplish this, half of the
sculpture is nestled into a base of soft plasticine
clay; the other exposed half is painted evenly with a clear, viscous
rubber. (Polyurethane rubber is best for single or small editions
while larger editions require silicone rubber.) When the half painted
with rubber dries, a protective and rock hard "mother mold"
made of reinforced plaster is built around the pliable rubber. The
sculpture is then turned over, and the process repeated. When the
second side is complete, the mold is opened and the original removed
from within. The rubber is rejoined with the other half, rendering
an exact "negative" image of the sculpture in rubber. The mold is often done in several sections to
facilitate proper and even flow during the actual bronze pour.
THE WAX POSITIVE
The original
sculpture is now used exclusively as a reference point. From the
"negative" rubber mold, a wax "positive" must
be created. Wax is melted to about 210°F, poured into the
mold and evenly coated or "slushed"
inside. Slushing is repeated three times
using cooler wax each time to avoid melting the previous coat. Under
ideal conditions, the wax wall will be about 3/16" thick ---
any less might create flow problems for the bronze; any more will
result in a heavier than necessary sculpture. When the mold is opened
and the rubber peeled away, an almost perfect wax reproduction is
removed.
WAX CHASING · SPRUING & GATING
"Wax chasing"
is the delicate process of joining the wax pieces back together
to form a complete “positive” of the sculpture (including removing
seams and repairing imperfections with heated customized soldering
irons or tools: dental tools being ideal). Artists are very involved
at this juncture, checking the integrity of the wax and, after approving
it, signing the piece.
After the wax
is chased and approved by the artist, the piece is then advanced
to "Spruing" or "Gating." This is where channels, through which the molten
bronze will travel to the artwork, are added to the wax version. These channels are also made of wax.
"Vents"
(thin wax sticks) and "Gates" (thicker wax sticks) are
affixed to the wax reproduction with heated tools. Later in the
casting process, the space occupied by sprues
or gates become runways through which the metal flows and trapped
gas escapes. Distribution
of the bronze, low turbulence, ventilation and shrinkage are important
considerations in the science of gating and spruing.
INVESTING
"Investment"
is the process of building a rock-hard shell around the wax sculpture.
Later in the process, when the wax has been melted out, the investment
will serve as a mold for the molten bronze. For most of history,
an investment consisting of plaster, sand and water was used to
accomplish this task. In the last 15 years, a new technology called
ceramic shell has become the industry standard.
The ceramic
shell technique begins by dipping the gated wax into vats of slurry
followed immediately by a bath of sand. This process builds a very
thin wall of silica around the wax.
When repeated approximately 9 times, allowing for drying
time in between dips, a hard ceramic shell, about ½" thick,
forms around the wax.
Prior to the
invention of ceramic shell, solid plaster investment was used. To
invest by the solid plaster method: tarpaper was loosely wrapped
around the wax reproduction in the shape of a cylinder. The enclosed
space surrounding the wax was then filled with a wet plaster/sand
mixture. When the plaster hardened, the tarpaper was removed and
a solid plaster investment is ready for "de-wax." Whether ceramic shell or plaster is used to
make the shell, the wax is a "positive" which must disappear
in order to create a cavity or "negative" for the bronze
to fill. Thus the phrase "lost wax casting" comes from
the process of the wax being melted or "lost" from the
shell. Plaster built shells are "de-waxed" in a high-pressure
steam chamber known as an autoclave; ceramic invested shells are
de-waxed in a kiln.
THE POUR
A huge graphite
crucible, fired by a furnace, is filled with bronze ingots that
are melted. The metal begins to melt at 1700°F. Bronze "seizes"
(stops flowing) when confronted with cold, which might occur if
molten bronze was poured into a room temperature shell; therefore
at the same time the bronze is being blasted by a natural gas furnace,
the ceramic shell is heated in a kiln to approximately 1100°F.
When the "Dance
of the Pour" begins, the crucible is lifted by crane out of
the gas furnace. At the same time, the glowing ceramic shells are
brought out of the kiln to the pour area. Two artisans operate the
crane that holds the crucible in a "jacket." The artisan
with the controls is the "lead pour," the artisan maintaining
the crucible balance is known as the "deadman." A third member of the pour team pushes away
dross and slag on the surface of the molten bronze.
The entire
pour is very fast and ve ry
precise; one crucible of bronze holds 400 lbs and can fill one or
two large shells or ten or more small shells. The first pieces poured
are those with thin walls and intricate details; requiring hot,
fluid bronze to move throughout the channel system. The alloy cast
at Artworks is known as Silicon Bronze.
The metal is made up of the following elements: COPPER 94.0%,
MANGANESE 1.1%, SILICON 3.9%, TRACE ELEMENTS 1.0%.
Silicon is an additive that helps the "flowability"
of the bronze. It achieved widespread use during World War II when
lead and tin were in short supply.
DEVESTING
"Devesting"
is the process during which the investment is removed from the metal.
Approximately one hour after the pour, the piece is cool enough
to handle. Skill and strength are combined with hammers and power
chisels to knock the investment off the freshly solidified metal.
The gates and sprues must also
be removed with a high intensity electric arc that can cut through
the bronze like butter. The final step is to sandblast the fine investment
from the bronze. When clean, the sculpture advances to the metal
shop…
METAL CHASING & FINISHING
Like wax chasing,
bronze must also be chased or cleaned to address the slight imperfections
that may result from the casting or shell building process. On larger
sculptures, where assembly of cast sections is required, chasing
is essential to take down weld line formed by the joining of two
planes. Metal chasing usually
starts with large electric or pneumatic grinders to remove the bulk
of the unwanted metal. Then, more refined and smaller tools such
as die and pencil grinders are used to re-create the artist’s subtle
surface texture. Much as
a house needs a wood frame to stand, many monumental bronzes require
a stainless steel internal structure to support the bronze "skin."
Many larger than life-size sculptures are analyzed by a structural
engineer who recommends an inner support structure that can reinforce
the piece to withstand earthquakes and high winds.
PATINA
Patination is enhancement of bronze by the chemical application
of color. Three water soluble compounds form the basis for most
patinas: Ferric Nitrate produces reds and browns, Cupric Nitrate
creates the greens and blues and Sulphurated
Potash produces black.
Each foundry
develops its own proprietary (and carefully guarded) patinas that
result from a carefully orchestrated blend of different chemicals,
pigments and application technique. Wide ranges of colors, both
transparent and opaque, are available to the experienced patineur.
The final step is putting a thin coat of clear wax over the
bronze to enhance and preserve the patina.
http://www.youtube.com/watch?v=rR8HzIlhb7c
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