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

The last time I mentioned my bronze casting project, it was in the context of racing to the emergency ward of my local hospital with hot sculpting wax burns. Remember that?

Well, the burns may have healed, but my passion for bronze casting remains uncooled.

It has been an epic endeavour. So epic, in fact, that I’m going to split the process into three posts.

To start with, getting the wax positives out of plaster and silicon rubber moulds.

I won’t bore you with plaster mould making. It’s well and widely documented online. It basically involves sinking the objects you wish to cast into clay or plasticine and then pouring a plaster shell or jacket in two halves over your object.

For my eggs, I added a flexible inner mould of silicon rubber, a slightly eventful experience as one batch of silicon never set and I found my precious eggs drowning in the most astonishing hollywood-style alien goo.

You can see what I ended up with below. Both my plaster-only egg carton mould and my outer plaster jacket for my egg moulds are soaking in a sink. Soaking the moulds in water makes them separate from their wax inners much more easily.

The plaster egg carton mould was really quite astonishing. The level of detail that it carried was exquisite. Carrying all five kilos of it around Sydney’s inner East between pours was less pleasurable.

Below you can see the inner silicon rubber moulds for my eggs, plus some early and unsuccessful wax castings of the egg carton and eggs.

The soaked moulds were reassembled, their edges plugged with clay to minimise leaks, and the two halves of the moulds were strapped together with rubber inner tyres to hold them rigid. The wax was poured in a number of layers, basically by filling the moulds with wax for a minute, then pouring the remaining liquid wax back out and then repeating. I found that particularly on a complex mould like the egg carton this process yielded a far more even result.

Interestingly, despite popular wisdom, I found that I got far better detail from pouring wax straight into my moulds rather than brushing on a thin first coat of wax. Perhaps it was because I was working with fairly small moulds with high levels of detail, but I really can’t speak with any particular authority on why this may be.

Once the moulds had been filled with wax they were submerged in water to cool the wax more quickly. You can see the rough unfinished results below.

The final process was finishing the wax. Holes were plugged with small additional pieces of wax. Because I found it difficult getting a perfect and complete casting of the egg carton I poured two positives and harvested all the necessary extra pieces from the second pour. You can also see small sections of lighter, softer wax which I used to even out small scratches on the positive.

The eggs were finished with baby oil which softened the surface of the wax and created a smooth, glossy finish.

The end result was really quite lovely. It looked like the sculpture had been formed out of rich dark chocolate.

It was with some regret that I wrapped my beautiful wax positives up in an old tea towel and sent them off to the foundry, as I knew my lovely waxes were marching to their death, and would soon be melted away.

But all for a fine cause, as you’ll see in Part Two.

To be continued.


~ by Niccola on June 8, 2010.

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

  1. […] in our last exciting installment, we farewelled the very lovely wax positive as it took its final journey to the foundry. What […]

  2. […] 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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