Complex sentence: Some of the protests turned on the fact that the actual sculptung was being done by Italian artisans in Berlin while artists of the Berliner Bildhauerschule just provided models in plaster or clay.
Split into simpler sentences: Some of the protests reached out to the fact, that the actual sculpturing was being done by Italian artisans in Berlin. The artists of the Berliner Bildhauerschule just provided models in plaster or clay.