Like several scientists, Isaac Newton has been represented many times over many different periods, and portraits of Newton were often commissioned by the scientist himself. These portraits tell us a lot about the scientist, the artist and the cultural context. This article examines two very different portraits of Newton that were realized more than a century apart, to show how the observer's attention can be focused on the history of physics, the history of art, their relationships and the use of the history of science in science education.