Part 3 – Casting in Metal

For our purposes, creating a brand new piece like the Magicicada, involves a two-stage casting process. The first stage – which we’ll cover this month – creates a Master casting in metal, while the second stage, uses the re-worked Master casting to create a latex mold from which derivative castings can be made.

To enable the metal casting process to be carried out, a negative of the wax Magicicada must be created.

To do this, small wax connectors called ‘sprues’ are attached to the original sculpture which in turn are connected to a central wax core. The purpose of these wax connections is to eventually provide a route into which the molten metal can flow.

Once complete, this ‘wax tree’ together with the original wax Magicicada is placed in a flask and filled with a silica-based, investment slurry. This mixture fills the flask and submerges the ‘wax tree’ leaving only it’s main ‘trunk’ protruding through the top of the liquid.

The flask is then subjected to a vacuum which draws trapped air from out of the mixture, ensuring all voids are filled and no air pockets remain.

After a short while, the investment slurry begins to stiffen in the flask, encasing the original wax Magicicada in a tomb-like, semi-solid block.

The flask containing the stiffened investment is then placed in a kiln and slowly heated in a process known as ‘burnout’.  This causes the interconnected ‘wax tree’  to melt and flow out from the investment block, leaving behind the vacant space it once occupied.

After all the wax has been ‘lost’ – and the original wax Magicicada destroyed – the investment block now contains a perfect 3 dimensional, negative of the original wax Magicicada – as well as a negative of the ‘wax tree’ that previously contained the sprues and connectors.

After several more hours in the kiln with temperatures slowly rising up to 1300F, the investment block will have hardened and be ready to cope with the stresses of molten metal being poured into it.

While the investment block is being heated, bronze is melted in a furnace at temperatures up to 2000F. When it’s time to pour,  the hot and hardened investment block is removed from the kiln and the molten bronze is poured in directly.

The molten metal flows into the empty passageways previously formed by the sprues and connectors of the ‘wax tree’ and fills all the cavities including those previously occupied by the original wax Magicicada. 

As the molten metal is being poured, a vacuum is applied to the investment block, which helps the metal flow into every cavity of the investment block, ensuring the details of the original wax sculpture are replicated as closely as possible

After the metal has solidified but before it cools, the flask containing the investment block is quenched in cold water. This conveniently dissolves investment, exposing the newly transformed Magicicada to the world for the first time!

While the casting process faithfully re-creates the detail of the original wax Magicicada, limitations of working with soft wax means it isn’t possible to incorporate every single detail that I might want to include.

Since bronze is much harder and more resilient in terms of retaining its shape and form, these additional details can be added by hand-sculpting and shaping the metal.

What results is a Master version of the Magicicada that will be used to create a latex mold – from which multiple, new Magicicadas can be produced.

>> Part 4 – Mold Making

Would you like a Magicicada smilar to the one
featured in this article?


Click for more information