Depending on the sculpture, up to 20 different operations are needed until a finished work of art made of metal is produced from the original model. Three methods are most frequently used:
Block mould with plaster fireclay
To create the wax positive, both silicone halves are carefully painted with wax, then both halves of the negative mould are joined together and filled with hot wax. After a few minutes of cooling, a solid layer of wax is created. The excess wax is poured out again, thus producing a hollow wax model. This "wax blank" is unpacked from the negative mould, filled with a plaster fireclay core, retouched by the artist again and then provided with sprues and risers. The entire object is covered with plaster fireclay, thus creating the fireclay mould necessary for casting. This is burned out in a kiln for 3-4 days at up to 750°C until the wax melts out and the fireclay mould, including its cavities, is completely burnt. In the next step, the liquid bronze is heated in the furnace at max. 1250°C, released from the slag and then poured into the cavities of the burned out mould in one go. After the model has solidified, the fireclay block is shattered to expose the cast work of art. Many artists want to experience the moment when their sculpture is cast.
Ceramic shell moulding process
The ceramic method is used for special requirements placed on the part to be cast. In this case, the mould is made of ceramic material instead of plaster fireclay. The hollow wax model produced from the flexible negative mould is provided with sprues and risers and, depending on its size, dipped into the ceramic mass four to six times and then dried. The resulting shell, which reaches a thickness of 6 mm to 10 mm, is melted out in a steam autoclave and fired in a kiln at 800°C. The shell thus reaches the hardness necessary to be filled with the liquid metal. After (quickly) solidifying, the ceramic shell is shattered to expose the cast work of art.
Ceramic method with vacuum assistance
The vacuum cuvette casting technique is preferred for complex models, such as sophisticated technical parts and jewellery. The wax blanks are provided with relatively few sprues as the metal flows vacuum-assisted into the mould. After installing the sprues, the wax model is placed into a stainless steel cylinder and cast in plaster-bound moulding material until the cylindrical mould form is filled. This moulding material is then mixed and poured under vacuum. After the material sets, the model is melted out in a kiln in a process lasting several hours and then burned. The still warm mould is placed into a pouring vessel and then a vacuum is created. The liquid metal virtually shoots into the cavity and fills it with great precision. After cooling down, the casting is carefully washed out of the stainless steel cylinder. This complex process allows intricate castings with 1-2 mm thickness to be created. Due to the nature of the process, the maximum size is limited to approx. 50 cm.