During his apprenticeship to Andrea Verrocchio (1468–1472), Leonardo learned how to paint—but his education didn't stop there! He was exposed to many different aspects of arts and craftsmanship, including three-dimensional techniques such as castings and sculptures. Leonardo was a bit biased in that he considered painting to be the true sign of genius in an artist, but sculpture was also a required part of his training. He viewed sculpture as being more mechanical, whereas he saw painting as more expressive and creative.