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A bronze frog – the lost wax casting method in pictures

Luisa Coscarelli

 

In my first year of the V&A/RCA History of Design MA Course we had the amazing opportunity to experience the process of casting bronze, and to make an object of cast bronze ourselves. In this post I will present the object that I made, and while many of the Object of the Week posts focus on the excellent craftsmanship, artistic eye and expertise for materials the respective objects display, this is not really the case here. I attempted to make a small bronze frog, and while I am satisfied with the outcome, I realise it is not of the highest artistic quality. However, as mentioned above this post is not so much concerned with the beauty of this object, but with the method of bronze casting.

Bronze Frog, Luisa Coscarelli, London, 2013, cast bronze with green stain, Image c Luisa Coscarelli.

Bronze Frog, Luisa Coscarelli, London, 2013, cast bronze with green stain. Image © Luisa Coscarelli, 2013.

In order to produce this object a method called Lost Wax Casting was used. A wax model is made, around which one builds up a ceramic shell. Once this is done the wax is burned out of the ceramic shell, which then functions as the mould for casting. This casting method usually implies that the object made is not reproducible, it is unique – first of all the wax model is lost, and secondly the ceramic shell that functions as a mould is also destroyed in the process. In addition, it is also a faster method of producing a casting mould. The images below outline this process in more detail.

Wax model for frog with wax funnel attached.

Wax model for frog with wax funnel attached. Image © Luisa Coscarelli, 2013.

Wax model for frog with wax funnel attached. Image © Luisa Coscarelli, 2013.

Wax model for frog with wax funnel attached. Image © Luisa Coscarelli, 2013.

After the wax model for the object has been made it needs to be prepared in order to be able to function as a mould. First of all, this means that a wax funnel needs to be attached to the object. The funnel allows the pouring of liquid bronze into the mould and needs to be attached at an angle so that the bronze is able to reach all parts of the object. At this stage, my frog would have not received enough bronze to his hind legs, so I attached extra funnel pathways as you can see in the images above. The red pieces of wax are air vents ensuring that as air is pushed forward by the liquid bronze it is able to escape via, eliminating the chance of air bubbles.

Image 4

Finished wax model complete with wax funnel and air vents. Image © Luisa Coscarelli, 2013.

Image 5

Finished wax model complete with wax funnel and air vents. Image © Luisa Coscarelli, 2013.

Image © Luisa Coscarelli, 2013.

Building of the ceramic shell. Image © Luisa Coscarelli, 2013.

Image © Luisa Coscarelli, 2013.

Building of the ceramic shell. Image © Luisa Coscarelli, 2013.

Once the wax model is completed, one can start work on the ceramic shell, which will eventually become the actual mould. This is a gradual process in which the ceramic layers are carefully built up. In order to do this, the wax piece is dipped into a slurry, which enables both powdered ceramic at first, and after a few days, coarser ceramic granules, to stick to the wax. After each layer of ceramic is applied, the model needs to dry and can be dipped again a day or so after.

Image 8

The finished ceramic shells. Image © Luisa Coscarelli, 2013.

Image 9

The finished ceramic shells. Image © Luisa Coscarelli, 2013.

Once the ceramic shells have completely dried, they are ready to be sent to a specific type of oven which burns out the wax models inside them, hence the name of the technique: Lost Wax casting. The ceramic shells have now become the negative into which the bronze can be poured in order to create the object. During the process of heating the moulds in order to get rid off the wax, they may crack and show signs of weakness. The cracks are covered up with clay, and additionally the edges of the objects are reinforced with it too. Now they are ready for the bronze.

Image © Luisa Coscarelli, 2013.

Scrap bronze being weighed. Image © Luisa Coscarelli, 2013.

The finished ceramic shells. Image © Luisa Coscarelli, 2013.

Scrap bronze being filled into the crucible. Image © Luisa Coscarelli, 2013.

Image 12

The hot liquid bronze. Image © Luisa Coscarelli, 2013.

Image 13

The pouring process of the hot liquid bronze. Image © Luisa Coscarelli, 2013.

After the appropriate amount of bronze has been weighed out, it is packed into the crucible and heated until red hot. The moulds have already been placed into a bucket with sand in order to stabilise them once the hot bronze is poured into them.

Hot and cold bronze in the moulds.

Hot bronze in the moulds. Image © Luisa Coscarelli, 2013.

Hot and cold bronze in the moulds.

Cold bronze in the moulds. Image © Luisa Coscarelli, 2013.

Bronze Frog with and without funnel.

Bronze Frog with funnel. Image © Luisa Coscarelli, 2013.

Bronze Frog with and without funnel.

Bronze Frog without funnel. Image © Luisa Coscarelli, 2013.

After the bronze cools completely – a process that can be helped along with ice cold water – the ceramic shell around it is broken and cleaned away from the bronze inside. The images above show the appearance of the bronze shortly after casting. Once the ceramic shell is cleared away, the funnel and air vents need to be removed from the object. In order to smooth it out, a process called sandblasting is employed. Blasting the object with sand removes the first layer of bronze and any impurities in it, whilst also making it smooth.

Images 18 & 19: The frog in the sandblaster and after the sandblasting process.

The frog in the sandblaster. Image © Luisa Coscarelli, 2013.

Images 18 & 19: The frog in the sandblaster and after the sandblasting process.

The frog after the sandblasting process. Image © Luisa Coscarelli, 2013.

Image 20

Frog with green stain freshly applied. Image © Luisa Coscarelli, 2013.

Image 21

Frog polished. Image © Luisa Coscarelli, 2013.

After sandblasting the object, the bronze looks more like a matte gold. Wanting to keep the material like this, however, would require daily polishing. This is why at this point a stain is usually applied to the bronze – in this case a green stain. Afterwards the object is polished and finally ready to be displayed or appreciated in the home.

 

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Have you seen any objects that intrigued you lately? Perhaps you have encountered something that piqued your curiosity in a museum or gallery (or in a shop or in the street?), or as part of your art or design practice, as part of your research, or as part of your daily life. Please don’t be shy! We welcome submissions on objects of all sorts, between 500 and 1,500 words, and we do ask that you own the rights to your images or use those belonging to the V&A.  If you aren’t sure if your idea is right for our column, it certainly never hurts to ask, so please get in touch with us:objectoftheweek@gmail.com

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Luisa Coscarelli –

Luisa did her BA in History of Art and German Literature at the Humboldt University in Berlin. Although completing it with a focus on contemporary art, she has now joined the Renaissance strand and is now interested in the relationship between smell and design. For her dissertation, Luisa is asking questions about ‘smelly objects’, and how olfactory environments were designed in the Renaissance period.

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© Luisa Coscarelli 2014. All Rights Reserved.

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