'Modelling in clay is to the sculptor what drawing on paper is to the painter… In the soft clay the genius of the artist is seen in its utmost purity and truth…'
Johann Joachi, Winckelmann, History of Art, 1776
Images and quote above are from the Victoria and Albert Museum website
From the The Metropolitan Museum of Art website
Bernini in Action: Gesture and Technique in Clay
In conjunction with the exhibition Bernini: Sculpting in Clay (on view October 3, 2012–January 6, 2013), Anthony Sigel, Guest Curator, and Conservator of Objects and Sculpture, Straus Center for Conservation and Technical Studies, Harvard Art Museums, outlines the research and discoveries he and his fellow curators made in preparation for the exhibition. By researching Bernini's methods, Sigel has determined which figures Bernini created himself and which ones were likely created by assistants. His lecture includes his own photographs of the models and detailed descriptions of Bernini's methods.