Verde Gris
"the green of Greece"
The green colouration (or
patina) seen on bronze statues and copper roofs is called verde gris
(verdigris). It is a chemical reaction copper, brass & bronze undergo
when exposed to the weather (and other factors like saltwater, pollution,
and situations where galvanic action occurs i.e. in contact with ferrous
metals). It is not corrosive like rust (although the Italians refer
to verdigris as "noble rust"). It is considered poisonous,
and has been used both as a fungicide and a medicine. This hallmark
powdery green patina is highly prized by collectors and difficult to
achieve successfully with chemical substitutes.
The following gives
a general timeline for the beginnings of a light green patina:
7-9 years in saline climates (i.e. near the coast)
5-8 years near heavy industry
10-14 years in urban areas
30 years or more in a clean environment
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Copper
Periodic
symbol: Cu
Atomic number: 29
Melting Point: 1083°C (1981.4°F) |
Copper
is prized for being non-corrosive, malleable, ductile, conductive,
easy to gild, and antimicrobrial.
The most common Alloys of copper are bronze
and brass. Bronze
is copper mixed with tin, Brass is copper
mixed with zinc. There is evidence that copper was first used
10,000 years ago.
As
an example of a modern use for copper, your pc includes about
6.85 lbs of copper (with 90% said to be from recycled sources).
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Repousse
Hammered Copper
Répoussé
literally means "to work from behind", however, today
it generally refers to both the metalsmithing techniques of embossing
and chasing.
Répoussé on a Monumental Scale
The largest répoussé copper sculpture in the world
is the Statue of Liberty. Given as a present to the United States
from France in 1884, this symbolic monument stands from base to
torch 152' 2" (46.84m) tall. The copper sheets are 3/32 inches
(2.37mm) thick and are laid over a steel infrastructure.
The
second largest repousse sculpture is Oregon's Portlandia, which
measures 35 ft tall.
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Greens use only the finest
quality .5mm (16 ounce) copper available in England. All work is brazed
rather than lead soldered for strength. Brass and bronze fittings
are standard and only 23½K double thick English gold leaf is applied.
No lacquers or fake patinas are used. A 3/4 inch solid bronze bearing
is incorporated into the body of every weathervane. Marine grade stainless
steel is provided.
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Gold
Periodic symbol:
Au
Atomic number: 79
Melting Point: 1064.43°C |
Gold
Leaf
1.27x10^-5cm
thick
Although
ornaments wrought in gold have been dated from 4,000BC, the Egyptians
were the first gilders. Thin sheets of of gold were created by
beating them with round stones, Modern techniques for creating
gold leaf have remained largely unchanged from this 1200BC Egyptian
process, aside from the introduction of metal hammers.
Greens
Weathervanes use 23.5 K double thick English Gold Leaf. The sheets
of loose leaf gold are applied to the copper's surface using a
squirrel hair gilder's tip. The copper's surface is first prepared
by cleaning, priming, and sizing using a 12 hour oil-based size.
It is the sizing which, when tacky bonds the gold to the copper.
Finally the gold is burnished.
The
manufacturer recommends regilding after 20-30 years.
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opper Mining in the UK
Historically,
Britain has played a central role in copper production since pre-Roman
times, becoming the world's 4th largest copper producer during much of
the 19th century. Today there are no active copper mines in Britain; however
the evidence of copper mining, in SW England and NW Wales, can be dated
as far back as the Bronze Age. Notably, trade in copper and tin was carried
out between Britain (Cornwall) and the Phoenicians as early as 1500 BC,
with Britain, at the time, referred to as the 'Cassiterides' -the 'Tin
Islands'.
the largest
copper mine in the world today is in Chile.
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