Morgenbladet 20. october 1907
Vigeland’s bronze sculptures were cast by professional foundries, principally by Christiania Art and Metal Foundry. The bronze alloy used was composed of 90% copper, 6% tin, 2% zinc, and 2% lead. They used the sand casting method.
The point of departure for bronze casting was the original plaster master copy. The master copy was half buried in a moulding box, which was an iron frame filled with natural very fine-grained sand. The exposed part of the sculpture was coated with a release agent similar to talc and then covered with sand section by section; if the sculptural form was complicated, only small sections were covered; the simpler the form, the larger the section. The damp and sticky sand was beaten onto the master cast until it was packed tightly around the cast.
When the complete surface was covered, the moulding box was placed over it in order to hold the sections in place. Then the moulding box on the other side was removed and the process repeated. The result was a plaster cast covered with smaller and larger sections, held together by two moulding boxes. The two moulding boxes were then parted from each other (and the sections loosened individually) and the master copy removed before the frames were reassembled. This resulted in a casting mould.
In order to make a hollow bronze cast, a core of form sand was made. This was done by casting a sand model from the plaster cast . A few millimetres were scraped off the surface of the sand cast before it was placed into the casting form as a core held in place by long spikes. The hollow space between the mould and the core was then filled with melted bronze.