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Copper does
not pour well when molten, but when tin is combined with
copper it both flows better, becomes a harder metal, and
some believe becomes more attractive. In the foundry process,
gases from the molten metal are created in the melting process
and these can leave an uneven and pitted surface when the
bronze is poured into the ceramic shell. Copper/phosphate
and other powders were historically added to bronze to remedy
this problem.
Modern bronze
foundries have developed silicon bronze as an art bronze
that is durable over time, aesthetic, well pouring and is
resistant to the pitting associated with foundry gases.
This modern silicon bronze is an alloy that addresses the
many different and complex properties of an art bronze.
The Everdur
silicone bronze for Dr. Irving's limited edition sculptures
is approximately 94 percent copper, 4 percent silicon, 1
percent manganese, with the remainder tin, lead, zinc, nickel,
iron and aluminum.
Applying Patina
After all the pieces of the newly cast bronze are cleaned
up, the colour or "bronze patina" will be applied.
Patina is the colour that naturally
takes place on raw bronze as it ages over a long period
of time.
Sculptors short cut the patina aging
process and gain far more control of the patina color through
the application of various chemicals on heated bronze. The
patina is slowly built up to a rich colour through the repeated
application of various chemical solutions accompanied with
heat.
After the right patina colour is arrived
at, it is brought out further with the application of a
paste wax.
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ABOUT
BRONZE
