Leonardo da Vinci's angel that can be seen within his masterpiece, the Virgin of the Rocks is arguably more difficult to paint than his more renowned piece, the Mona Lisa. One only has to view this exquisite portrait painting to see why. The angel's face is not only inclined, but orientated in a three-quarter view, posing challenges in rendering her features. The lighting is subtle yet full of drama and colour. Shadows shift in ethereal ways; greens and crimsons condense between light and shadow. And the hair resembles spun gold. How can the developing portraitist take on such a challenge?...