Ashanti Casting Technique

Transcription

1 Ashanti Casting Technique

2 The Ashanti casting technique was developed by the Akan Ashanti people who live in Ghana. This technique is a lost wax casting method known as fonte à cire perdue or lost wax casting. The lost wax method has been used for around 6,000 years and is still used in various ways today to cast metal for industrial, craft and art applications. It is mainly used for copper, silver and gold alloys. The procedure is always the same: First the object that is to be made out of metal is shaped in wax. The wax used is beeswax, today also with industrially manufactured wax sheets, wire, profiles or blocks that can be drilled, milled and ground. When the wax model has been shaped, casting and normally also additional venting channels are provided. The finished model is then covered with a shell of a fireproof moulding compound. Only the ends of the channels protrude from one side of the mould. When the casting mould has dried, it is heated upside down so that the wax can flow from the channels. Molten metal that has been heated in a separate crucible is then poured into the resulting hollow mould, the negative mould of the wax model. As soon as the metal has solidified, the mould is broken and the object previously created from wax is then recreated as a unique metal piece. The wax model can only be used once and must be re-made for each new cast, as the shape is lost when the wax is melted. If the cast is unsuccessful, a new wax model must be created. The special feature of the Ashanti casting technique is that the casting mould described above and the melting crucible are inseparably connected. As a result the metal is melted without exposure to the oxidising ambient air and cast in an enclosed system by turning the mould. With this clever method, thin-walled objects can be made with great attention to detail without the use of complicated apparatus. The model is made of beeswax, the casting mould and the crucible of clay with varying amounts of charcoal and horse manure. The following pages contain a series of images and a description of how a bangle is crafted with the Ashanti casting technique.

3 Technical description The fireproof clay cores are shaped, dried and fired. The fired core is shaped by filing and sanding. The core is finished. This is superficially covered in wax.

4 Finished wax model of the bangle. The core of fireproof clay is covered in wax. The wave pattern is already cut out around the bangle. The casting channels made of wax wire are fitted. The mould is ready for the first coating of clay and charcoal slip. The first shaping coating is painted on with a brush and hangs in the shade of a tree to dry. The mould is covered with the third and last layer of the clay and charcoal slip and dried. It is then covered carefully in stages with a supporting shell made of a mixture of fireproof clay, fireclay and horse manure. The mould is dried after every stage.

5 The clay mixture is applied without moistening the underlying layer too much, as the mould is brittle when it has not been fired. The wax model is covered and ready for melting the wax. The funnel-shaped upper section of the melting crucible is mounted on the side of the converging casting channels. The casting moulds are slowly heated in the charcoal embers with the crucible side facing downwards until the wax starts to run out and burns, producing smoke. The model, the wax, is then "lost" and a hollow mould is then ready for the molten metal.

6 The melted casting mould is covered and reinforced with a second layer of clay. The casting opening is closed with a thin wax tablet to prevent any contaminants entering the hollow mould. The metal is then weighed in pieces in accordance with the wax weight and filled into the crucible. Suitable crucible covers are ready to close the mould. The casting mould is ready for the last layer of fireproof clay. Finished casting moulds.

7 The melting furnace heated with charcoal is ready for use. The combustion air is supplied with bellows on the underside of the furnace. The casting moulds are placed upside down into the furnace and covered with charcoal. The furnace is fired until the embers have reached the top. It is alternately stirred and stoked until the metal has melted. The glowing casting mould is pushed out of the furnace and then turned so that the molten metal flows into the hollow mould. The mould is cooled very slowly overnight in the ashes.

8 After cooling the most exciting moment has arrived - the clay shell is broken open, first carefully on the crucible side to check whether the metal has run completely into the shell. The mould side is then split with a clean knock. The casting process was successful. The model is also completely filled with the gold alloy! The casting channels are then separated and the dark oxide layer is removed with citric acid and alum.

9 Bibliography Max Fröhlich: Gelbgiesser im Kameruner Grasland, 1979 Museum Rietberg, Zurich E. Fischer / H. Himmelheber / M. Fröhlich: Das Gold in der Kunst Westafrikas / Zur Technik des Goldgusses bei den Ashanti, 1981 Museum Rietberg, Zurich Max Fröhlich: Cire-Perdue-Guss / Lost-wax casting, 1995 Zürich Johanna Dahm: Lost and Found, 1999 Verlag Niggli, ISBN: Johanna Dahm: same same, but different, 2008 Verlag Niggli, ISBN Das Gold der Akan, Museum Liaunig, 2008 HL Museumsverwaltung GmbH, ISBN Georg Eisner: Wunderwerke westafrikanischer Goldgiesserkunst, 2012 CH-Bollingen

10 Moritz Ganzoni