About plaster casting
Vigeland began his casting in plaster by making a small-scale model. His smiths made an iron armature in full scale, using a grid over the model. They bound wooden crosses with steel wire to stop the clay from slipping when the sculpture was built up around the armature. Vigeland modelled by hand, but also used several types of rudimentary tools. Points from the plaster sketch were transferred to the clay model using the grid, a meter ruler and callipers. Finally the sculpture was reworked with finer tools to achieve the desired surface.
While the clay was still soft and damp, thin metal plates (shims) were stuck into the clay surface of the sculpture before it was covered with a thin layer of coloured plaster. The shims divided the plaster mould that was to be made from the clay original into a main mould and several minor moulds.
Then an armature reinforcement was made by bending iron bars and attaching them with plaster to the different parts, before more plaster, (uncoloured) was put over the initial layer of plaster. The outer edges of the shims could then be seen as seams in the surface of the mould. The minor moulds were marked before they were prised loose with the help of several sorts of thin specialist tools and water. The clay was then dug out of the main mould. Subsequently the inner iron armature was removed.
The minor moulds were marked before they were prised loose with the help of several sorts of thin specialist tools and water. The clay was then dug out of the main mould. Subsequently the inner iron armature was removed. The main mould and all the minor moulds were cleaned and reassembled. The casting mould was ready to be used.
The inside of the mould was coated with a release agent and then covered with an approximately two cm layer of plaster. The plaster cast was reinforced internally with wooden supports and sacking. When the plaster set, the mould was hacked away with a blunt chisel and wooden mallet. The result was a master copy identical to the clay original.