Such is the field upon which the mouth in portraiture has been debated: an ongoing conflict between the serious and the smirk. The most famous and enduring portrait in the world functions around this very conflict. Millions of words have been devoted to the Mona Lisa and her smirk – more generously known as her ‘enigmatic smile’ — and so today it’s difficult to write about her without sensing that you’re at the back of a very long and noisy queue that stretches all the way back to 16th century Florence.