Complex sentence: In 1845, Etty took a smaller copy of "The Combat", which had been painted by an unknown Edinburgh artist, and completely reworked it to serve as the basis for an engraving by George Thomas Doo, which was published in 1848.
Split into simpler sentences: In 1845, Etty took a smaller version of "The Combat", which had been painted by an unknown Edinburgh artist. Etty completely reworked this version to serve as the basis for an engraving by George Thomas Doo, which was published in 1848.