Enduring Bronze -
The Metal of the Ages
Traditional Bronze is a copper alloy with up to 10% tin.
The tin in bronze makes it more resistant to wear than
unalloyed copper. Bronzes today are usually stronger and
more resistant to corrosion than brass.
Contemporary bronzes are typically copper alloys that
may contain silicon, manganese, aluminium, lead, iron
and other elements, with or without tin.
The variations in bronze composition significantly affect
its characteristics. Durability, machine ability,
corrosion-resistance and ductility for deep drawing are
|Bronze Grade A
5% 1922° F.
Copper - Tin alloy
from 3% tin (mild bronze) to 25% tin (bell metals)
The first metal used by man was copper so it is natural that the
first alloys widely used were copper alloys. The two alloys of
most significance are bronze and brass. Bronze is an alloy of
copper and tin, while brass is an alloy of copper and zinc.
Recently many objects, thought to be bronze, have been found to
be brass. Since the patina and color of bronze and brass are
almost indistinguishable from each other.
All copper-tin alloys with more than 78% copper are called
bronzes. They are chemically very stable. When in dry air the
metal does not change at all, while in moist air they produce a
beautiful, green, pore-free, surface film (patina) which protects
the layers it covers from corrosion.
The tin content makes the alloy hard, bronzes with 6% tin can still
be rolled, or hammered, while bronzes with 10-20% tin are
usually require casting. Bronzes with more than 20% tin are used
for bell casting, these alloys are hard and rather brittle, but when
struck they emit a clear note. Even higher tin content (up to 40%)
produces radiantly white alloys; like the bell alloys these are
brittle and hard, but accept a beautiful polish. They were used for
bronze mirrors even in antiquity, and today are called speculum
ready to be fired.
Weathering and Patination:
The oxidation process that gives Bronze its characteristic
green patina is a result of exposure to an acidic
atmosphere. The process is, therefore, faster in some
metropolitan, marine, and industrial areas, where higher
concentrations of pollutants exist. When acidic moisture
comes in contact with exposed Bronze surfaces, it reacts
with the copper to form copper sulfate. The acid is
neutralized during the reaction with the copper. This patina
eventually covers the surface and adheres tightly to it, thus
providing a protective layer against further weathering.
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|Bronze plaques are manufactured using sand
molds in a state-of-the-art foundry from raw ingot
alloyed in the following materials:
- Copper Alloy C92200;
- 88% copper, 6% tin, 4% zinc, 2% lead.
Bronze plaques are the choice for interior as well as
exterior applications. Although the finish of bronze will
naturally patina over time, the material itself will not
deteriorate. Objects made from bronze have been found
submerged in seawater for over 3000 years still in excellent
The weight of a bronze plaque may be roughly
estimated by calculating the following formula:
(height x width x depth) x .31.
For most smaller plaques (under 36" x 30") allow
.25" as the approximate depth.
Use .375" for plaques over 36" x 30".
About 3,500 BC true bronze started to appear. This true bronze was
harder and less brittle than copper-arsenic bronzes, could be made
copper and tin ingots if the natural materials were not available, and
could be made the same every time.
Bronze was widely used for utilitarian and artistic purposes until iron
became cheaper and more plentiful. Bronze continued to have wide
utilitarian uses until it became cost prohibitive, now except for a few
applications as a bearing metal in the engineering and automobile
industries has fallen out of use. Artistically bronze is still widely used
in casting sculptures of all sizes, plaques, and bell founding.
Bronze was the first alloy intentionally
manufactured and used by man. Early bronze
was an alloy of copper and arsenic that occur
together naturally, and was used from about
4,000 BC until about 3,500 BC. While we do
not really know, the copper-arsenic alloys
probably fell of favor because:
1. They were unpredictable in composition,
giving unpredictable properties to the finished
2. The smelting process releases arsenic gas,
probably killing the metalworkers and causing
the uses to think the metal was evil.
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