Friday, September 28, 2018

A Bit About Bronze

"Ferdinando I de Medici" 1608.
Giambologna and Pietro Tacca
(Piazza of the Annunziata, Florence, Italy)

Copyright © Edward Riojas

Not all that glitters is gold. Sometimes it’s bronze.

I learned a bit about bronze while working on a recent project. Having previous experience in small-scale casting for a jewelry class, I decided in this case to use an art foundry’s services. The latest project was above my experience and pay grade, and I simply didn’t have any blast furnaces hanging about. Partially to keep costs down and partially to get my hands dirty, I decided to finish the piece myself. So it was that I drove to Ann Arbor to collect my [cut up] original wax model, its master mold, and three raw casts.

The color of the fresh bronze castings was a little surprising. It was a bright color that could have easily passed for gold, even though the alloy is mostly copper with a bit of tin.

To modern eyes, that is not what we expect of bronze. It is a peculiar thing that, unlike other art media, our perception of bronze is based solely on antiquity. The fine art world, for example, lauds the restoration and cleaning of old oil paintings. Not so with bronze. Even our language supports this skewed view of the alloy. To have “bronzed skin” is to have spent many hours in the sun. No one, on the other hand, wants to be as sparkly as an engagement ring. That’s just silly.

What would otherwise be simple corrosion or rust is known as “patina” in the bronze world. Bronze sculptures that have been sitting around for hundreds of years all have a patina of brown and/or green and, for some odd reason, this oxidation is desirable for even the newest of bronze pieces.

Natural oxidation, however, takes eons. Enter chemical patinas. There are various ways of quickly producing a patina, but I used a traditional method for my project – ferric oxide applied on the heated piece, with a later application of colored buffing wax. What would otherwise have taken a century or more was accomplished in less than an hour.

Bronze has long been a popular sculpting medium, in part because the heated metal expands when in the mold, thus filling every detail, and because the same metal shrinks when cooling, making it easy to remove from the mold.

In antiquity, however, bronze was also a favorite material for producing military hardware. Hence, many ancient bronze sculptures were lost forever to invading armies, who melted down the bronze and re-cast it into cannons.

Two, however, can play that game. The equestrian monument of Ferdinando I de Medici in Florence, for example, is said to have been produced with Turkish cannons captured by the Knights of San Stefano. Stories like that are golden.

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