How to magically transform a bronze bar into an egg carton – Part Two

Yep, emphasis on “magically”.

A spot of history for you… In the fourth millennium BC (BC!!!) some very smart metal workers discovered bronze, an alloy of copper and (at the time) arsenic. These days, a number of elements are used instead of arsenic, which is extremely poisonous, so that’s reassuring. These elements include tin, zinc, silica, nickel and zinc among others.

Some 6000 years later, I discovered bronze, and was pretty bloody chuffed about it, so I can only assume that its original creators felt a quiet sense of achievement at the time.

Understatement of the millennium.

On our field trip to Crawfords Foundry in South Strathfield, the word everyone used to describe the experience was “mediaeval”. Men striding around clad head to toe in leather, a strange cauldron emitting an eery green glow, I certainly wouldn’t have been surprised if these guys turned out to be alchemists. The whole thing was magical. Utterly magical.

So, how do they do it?

Well, in our last exciting installment, we farewelled the very lovely wax positive as it took its final journey to the foundry. What happens next?

First, the wax positive gets a ceramic shell applied to it in a series of coats. You can see a number of ceramic shells drying in the photo below.

The positive also has a number of tubes attached to it, some to feed the molten bronze into the base of the sculpture, and some to release the gasses that build up within the mould. You can see a fairly large bronze hanging and drying below.

The ceramic shells are then fired, and the wax drains away leaving a hollow mould behind (farewell, beautiful wax!). The hot shells sit in the kiln, ready to receive the molten bronze.

Now, the magic bit! Below, we see the foundry workers lifting the lid of the furnace, which emits the most incredible radiant orange light.

The crucible is lifted out…

The molten bronze is stirred…

The slag is poured off… (Oh, the joy of legitimately being able to use the word slag!).

The moulds are filled, hot from the kiln.

And here’s the egg carton!

The ceramic moulds all glow orange as they sit cooling.

To speed up the cooling process, cold water then gets poured over the moulds. The carton again…

After twenty minutes or so, the bronze is cool enough to work with. The ceramic shell is jack hammered to start to break it away from the bronze.

The remaining shell is then beaten off with hammers. You can see the six eggs below, still with their trees attached.

And here’s the carton. Removing the ceramic shell from its inner recesses took a great deal of jack hammering, drilling, chiseling, and sand blasting.

Bronze, at last! A great clean-up awaits, along with applying a patina.

To be continued.

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~ by Niccola on June 9, 2010.

One Response to “How to magically transform a bronze bar into an egg carton – Part Two”

  1. […] my work in bronze. It was a process that I described in incredible depth at the time. (Here, here, here and […]

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