Hidden marks beneath the Mona Lisa reveals Leonardo da Vinci ‘traced’ the outline of the iconic painting from an earlier sketch
We may never know the secret behind the Mona Lisa’s inscrutable smile — but Leonardo da Vinci’s iconic 1503 oil portrait has let slip one of its other secrets.
French researchers used a high-resolution camera that can capture light from beyond the visible spectrum to study the masterpiece is unprecedented detail.
The images revealed charcoal dots that are traces of a technique — known as ‘spolvero’, or ‘pouncing’ — used to transfer outlines from one sketch to a new panel.
While spolvero is a common technique, this is the first time that it has been conclusively proven that the final Mona Lisa was based on a preparatory sketch.
French researchers used a high-resolution camera that can capture light from beyond the visible spectrum to study the masterpiece is unprecedented detail. Pictured: the spolvero dots and hidden details seen under the Mona Lisa using a high-resolution, multispectral camera, along with the so-called ‘layer amplification method’, or LAM, to pick out the faint marks
The art technique of pouncing is not dissimilar to that of method used to copy an image via tracing paper, as might be familiar from school art classes.
To perform the transfer, the artist makes small holes — either directly into the original sketch, or into tracing paper placed over over it — tracing the outlines of the image as a series of tiny dots.
This perforated template is then placed over the final canvas and a powder — such as graphite, chalk or pastel — is forced through the holes, leaving a ‘join-the-dots’ style copy of the original sketch on the surface where the work will be finished.
Pouncing is ideal for use when one’s canvas is unforgiving of mistakes, such as when creating an engraving, or — in the case of the Mona Lisa — painting on poplar wood that had been painstakingly prepared over the course of up to a decade.
Leonardo — who learned his craft under fellow Italian master Andrea del Verrocchio — would have been accustomed to painting on such wooden panels which would have been dried and treated with a mix of glue, chalk and white pigment.
This creates a smooth, silky surface on which a work can be painted — with guidance from the spolvero dots transferred from preparatory sketches.
‘There are many spolveri in other portraits painted by Leonardo,’ explained paper authors Pascal Cotte and Lionel Simonot.
For instance, they continued, the tracing marks can be seen in ‘The Lady with an Ermine, Ginevra de’Benci and La Belle Ferronnière.’
‘Therefore, it was surprising that none were discovered [before] in Mona Lisa.’
The images revealed charcoal dots (best seen bottom right) that are traces of a technique — known as ‘spolvero’, or ‘pouncing’ — used to transfer outlines from one sketch to a new panel
The traces reveal the da Vinci made a number of changes to the Mona Lisa from his original sketch to the finished work.
In the near-infrared part of the spectrum, for example, the team found evidence that the fingers of Mona Lisa’s left hand had originally been intended to be in a slightly different position.
Cotte and Simonot also discovered evidence that the Mona Lisa was painted on a board previously used for an aborted project — such reuse would not have been uncommon, given the time and expense that went into preparing the poplar panels.