Complex sentence: The artists who produced these unique paintings used techniques not often seen in other cave art. Many of the paintings appear to have been made only after the walls were scraped clear of debris and concretions, leaving a smoother and noticeably lighter area upon which the artists worked.
Split into simpler sentences: The artists who produced these unique paintings used techniques not often seen in other cave art. Many of the paintings appear to have been made only after the walls were scraped clear of debris and concretions. This left a smoother and noticeably lighter area upon which the artists worked.