The sand moulding process
The sand moulding process derives its name from the moulding material used, moulding sand. In art casting, this process experienced a special heyday in the 19th century, during the time of the colossal monuments.
The starting point is the model created by the artist from sufficiently solid material, usually plaster or wood. After the model has been cut into the correct shape, the moulder, an artisan, begins his work. He moulds the model in moulding sand in two- or multi-part moulding boxes and a negative of the model is created.
As moulding sand is not elastic, all undercut parts of a model have to be moulded by sand parts that can be pulled out from the side, the so-called core pieces. The finished outer mould is taken apart again to remove the model, after the core pieces have been removed by means of the core fork and fitted back into the negative mould. An inner core, also made of moulding sand, is now carefully moulded into the cavity thus created. The core gets its stability from a core frame made of iron wire and iron rods. Initially, it fills the entire mould cavity, but in the next step, a few millimetres are removed to create the cavity between the core and the outer mould for the metal to flow in. After the mould and core have dried, the box is clamped tightly together and the liquid metal is poured into the cavity with the help of sprue and casting channels and risers.
The raw casting is removed from the broken mould and handed over to the chaser for finishing. With his special tools, he carries out the reworking. Sculptures cast in several parts are welded together. Casting burrs and welding seams are machined until they are practically invisible. The aim of this treatment is to match the casting as closely as possible to the original.
The final treatment of the bronze casting is done by the patineur. The desired patina is achieved by treatment with chemical solutions, which is preserved for as long as possible by wax or protective lacquer. The natural patina, however, which develops in the course of time outdoors, depends on the local conditions and its colour can hardly be influenced. However, with care and support, it will gain in beauty and intensity from year to year.