artfool nr 5/2013             

               A bronze oniontree





































































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7. The bronzefilled shells cooled surprisingly soon, and after an hour we could place them in water and a little later start chopping away the shells.


To the left you see my bronze sculpture with a little ceramic shell left in the middle. In the next photo I have sawed off two onions and sand- blasted everything.

1. Make a sculpture in wax. I had never used wax before and was surprised by its hardness: I could not form anything with my fingers although I had the right kind of wax bought through our course leader. I ended by carving slices with a knife and rolling these slices into four balls resembling onions or rose buds. Other course participants was able to form horses and detailed houses.

2. The sculptures one mounts on cuplike waxforms, which functions as funnels when the bronze is poured. One can put several sculptures on the same cup. One also has to attach waxpipes between small outstretched forms (channels) as exits for gases. The yellow part is the waxcup, the red channels and the black my waxsculptures.

3. The whole arrangement is covered with thin clay in many layers to form a shell 5-6 millimeters thick. This process takes days as each layer has to dry 12 to 24 hours before a new layer can be applied.


My future oniontree in the foreground to the left.

4. Now it is time to melt the wax out of the clay form. We used a gigantic gas flame for this. The wax drips down in a bucket and can be used again. The now empty clay shell is heated to 800 degree Celsius in a ceramic oven to sinter and become strong.

5. It is into those ceramic shells one pours melted bronze (1100 degree Celsius). It is now one understands the necessity of channels: the scupltures are standing upside down in sand and many therefore has thin forms in the bottom. If the bronze shall flow into the smallest parts before it cools, the air inside those small parts must have somewhere to go quickly outside the actual sculpture.

6. It needs training to pour the hot bronze into the shells. One must pour quickly so that the bronze is still hot enough for the last shell; we casted around 15 shells, with 3 or 4 times as many sculptures, at the same time. No shell cracked, so the casting was perfect.

8. Next step is to saw off the sculptures from the cup and from all channels – the bronze in those pieces are used again. Then it is just to clean, sand blast, polish and patinate as one wishes. I decided to keep two of my sculptures onto the cup as the whole came out as a little oniontree. I sawed off two that now are fallen down, while the other two can go on growing on their stem. Those fallen down I painted with sulphur liver to make them blacker, and the rest I made greenish.
In november I tested a new technique: bronze casting of sculptures. As I had no sculpture to cast, I had to make something only for this instance. Result: an oniontree with a couple of fallen down onions. Here I give an account of the steps in the method we used: bronze casting with ceramic shells and lost wax, with my photos (except in one case). It was the Artists collective workshop in Gothenburg (Konstnärernas kollektivverkstad, KKV) that arranged the course with sculptor Emma Ströde as teacher. 

This photo: Yvonne Swahn