Complex sentence: Head conservator at the Philadelphia Museum of Art Marigene Butler oversaw a 1983--89 multi-national research project investigating the painterly techniques of Philadelphia painting and its relationship to the Turin painting and oversaw further restoration.
Split into simpler sentences: Head conservator at the Philadelphia Museum of Art Marigene Butler oversaw a multi-national research project between 1983 and 1989. Her team investigated the painterly techniques of Philadelphia painting and its relationship to the Turin painting, while perfoming further restoration.