What the visitor is looking at, through glass and across the safety barrier, is the same poplar wood panel that Leonardo worked on for years, that traveled with him to France, that hung in royal palaces and in Napoleon’s apartments and on hooks in the Salon Carré. It is the same panel that Vincenzo Peruggia lifted from those hooks on a Monday morning in August 1911, carried to a service stairway, removed from its glass case, and took home under his coat.
It is, by any measure, one of the supreme achievements of Western painting — the sfumato technique at its greatest expression, the portrait as a form pushed to its furthest limits, the ambiguity of expression that has generated more commentary than perhaps any other single painterly effect in the history of art.
That the experience of standing in front of it is now so mediated — by glass, by distance, by crowds, by the weight of its celebrity — is itself partly a consequence of what happened over the two years it was missing. The theft created the celebrity that necessitates the protection that makes the painting harder to see. This circularity is one of the more poignant features of the story: the event that made the Mona Lisa universally famous also set in motion the conditions that make it, for the person standing in front of it, strangely difficult to actually see.
The smile, through bulletproof glass, across a crowded room, remains what it has always been: a question that the painting poses and does not answer, an expression suspended at the edge of meaning, neither fully welcoming nor fully withholding, as enigmatic in its current enclosure as it was when it hung on four iron hooks in the open gallery of the Louvre, available to anyone who walked past.