One of the quickest ways to mark the difference between an amateur and a professional artist is to check his or her handling of linear perspective. The rules of linear perspective being as logical and clear cut as they are, no artist claiming the rank of professional should exhibit any difficulty in utilising them. At a time during the fifteenth century when other artists were struggling to master the mere rudiments of this rediscovered drawing tool, Leonardo da Vinci was fascinated with a much more ephemeral form of perspective which we call today, "aerial" perspective. No, it has nothing to do with drawing antennas the right size or painting from an aeroplane window. Instead, it is about painting air. When was the last time you sat down and said to yourself, hmmmm, I think I'll paint some air today?
Yet just as the landscape painter must master linear perspective if he or she is in any way involved in the rendering of manmade structures, conversely, we might think of aerial perspective as the use of perspective to draw God-made or natural elements in a landscape. Take a look at the Mona Lisa--not the woman, the background. It's an interesting commentary on this masterpiece that the background may have been as great an influence on landscape painters as the figure has been for portrait painters. We see it in Leonardo's other work such as The Virgin and Child with St. Anne, painted around 1510-13. It's also noticeable in Leonardo's little-known Bacchus painted in 1515. Leonardo considered air to be blue (except in the Bacchus where he rendered it yellow for some reason).
Just as Alberti wrote the book on linear perspective, Leonardo could be said to have done the same with aerial perspective. His techniques, colours, and sensitivities to the effects of air and light upon distant landscapes were to have a profound effect upon artists for generations, even though landscape painting was largely relegated to imaginary backgrounds for a couple hundred years after Mona first cracked a grin. Perhaps she is smiling about the seemingly impossible landscape behind her marked by two different horizons and streams flowing in opposite directions, yet imbued with such exquisitely beautiful thin air as to make us hardly aware of the artist's vivid imagination running rampant across its mountains and valleys. Once we study Leonardo's form of perspective, we will never look at air quite the same again.