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Bronze work has never failed to
fascinate people. It finds wide applications, right from making
tools to artifacts.
An alloy of copper and tin, bronze was
made almost five thousand years ago. Until iron was developed,
that is for another two thousand years, bronze was used for
making weapons, armour, tools and other implements. However, it
was a rare alloy, until large deposits of tin were discovered
and there began an extensive trade in tin.
The proportion in which copper and tin
were used varied, depending upon the usage. The proportion of
copper used could be between sixty seven to ninety five percent.
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With the passage of time, scientists
had worked out what proportions would yield best results for
specific purposes. For instance, the proportion of copper to tin
was eight to one for bronze gunmetal, according to the
description of an alloy in an eleventh century Greek manuscript.
Nowadays bronze is made without using tin, substituting it with
aluminum, manganese or zinc. Bronze was extensively used in churches and
cathedrals, for making doors, vessels, candlesticks, and other
liturgical implements, during the Middle ages. It was used in homes
for making basins, chandeliers and fittings for furniture in the
late nineteenth century. Bronze sculptures are a rage today.
Properties
Bronze is harder than pure iron. It is also far more resistant
to corrosion. Of course, it is harder than copper too,
considering that it is the result of copper being alloyed with
another metal. Bronze melts |
A bronze statue |
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more easily, that is it is more
fusible, and therefore more easy to cast. However, it is not as
malleable as copper or silver and therefore cannot be forged
(pounded).
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The different kinds and their uses
There are different kinds of bronze and each has its specific
usage. An interesting truth is its use in making coins. Most copper
coins are actually bronze, containing about 4 per cent tin and 1 per
cent zinc.
Statuary bronze has a tin content of less
than ten per cent, plus a mixture of zinc and lead. Technically, it
becomes brass. The different kinds of manganese bronze have been
found extremely useful in mechanical engineering. It may or may not
contain tin. However, there is a considerable amount of zinc and
manganese. The manganese content may be around four and a half per
cent.
Sometimes, the hardness is increased by
adding a small amount of phosphorous. Then it becomes phosphorous
bronze. Phosphorous bronze contains one to two per cent phosphorous
in the ingot. When it is cast, there is a mere trace of phosphorous.
It is used for making valves, bushings etc.
When
copper is mixed with aluminum (up to a maximum percentage of
sixteen), along with other metals such as iron or nickel, it is
known as aluminum bronze. Aluminum bronze is particularly strong.
It is also corrosion resistant. It is used for making for making
pipe fittings, turbine blades, pumps, gears and ship propellers.
Bell metal is yet another kind of bronze.
What gives it a distinctiveness is its sonorous quality when struck.
Bell metal has a high percentage of tin, which could be anywhere
between twenty to twenty five per cent.
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