The cracks in a painting are a means of authentication and reveal the material and methods used by the artists, according to our partner
The Conversation
.
They are thus studied thanks to “multispectral imaging” which makes it possible to record the complete spectrum of colors, from ultraviolet to infrared, with extreme spectral precision.
This analysis was conducted by
Ludovic Pauchard
, CNRS researcher at the FAST laboratory (Fluids, Automation and Thermal Systems) at the University of Paris-Saclay.
It's the Mona Lisa you see in this image, made entirely of cracks and cracks.
Even without the colors, the crack patterns differ depending on the pigments and binders.
We can even see the cracks in the depth of the painting, for example on the forehead, whose parallel cracks are clearly distinguishable from those of the landscape or the sky which have no particular orientation.
Cracks are one of the alterations that memorize the life of a painting.
With a wide variety of morphologies in most easel paintings, they are of several interests to art historians and restorers.
First of all, it is a way to authenticate the paintings.
Analysis of Mona Lisa cracks recorded in photographs taken since 1880 helped authenticate the painting and dispel doubts expressed after the painting was stolen in 1911.
Cracks are a "fingerprint" of the artwork.
By attempting to reproduce them, a forger inevitably and involuntarily leaves the mark of his time.
Thus, chemical compounds discovered at a period much later than that attributed to a work could be used to develop cracks artificially.
The thorough classification of cracking in easel paints over the years is a way to discriminate between those that form during aging and those created in an accelerated way, for example by temperature variations.
The cracks don't lie!
Study cracks to better understand works and creative processes
The cracks are also indicative of the materials and methods used by the artists.
They are not formed randomly, but obey the laws of physics and mechanics: a crack spreads while being guided by the tensions of the environment (the fabric for example).
Once the tensions have been released, the organization of the cracks differs by several characteristics, such as their density or their orientation.
These characteristics are affected in particular by the rigidity and the thickness of the layers, and sometimes by the direction of the brushstrokes, the heterogeneities of the paint, as well as by the mode of solicitation of the paint: drying, aging of the paint, deformation inflicted by the support (wooden panel, canvas).
The cracks thus make it possible to obtain information on the whole of a table.
We study them using “multispectral imaging” which records the full spectrum of colors, from ultraviolet to infrared, with extreme spectral precision.
The cracks then appear as sudden variations in luminosity.
We are looking for them on all the multispectral images in order to locate and differentiate these alterations in depth in the pictorial layer (the paint layer, which can be heterogeneous with a mixture of pigments of different sizes and different rigidities, and solvents on different layers).
This imaging technique preserves the integrity of the work.
It is used in addition to structural analyzes of the pictorial material, with the help of analyzes of samples allowing, among other things, identification of the pigments used and other imaging techniques, such as fluorescence under UV lighting or X-ray for example.
For example, the image can highlight three specific regions.
The very visible vertical and parallel cracks in the forehead of Mona Lisa are very deep, up to the surface of the poplar panel constituting the support of the painting;
they have the same direction as that of the fibers of the wood.
Thus, these cracks seem strongly linked to the tensions transmitted by the support over time.
On the other hand, in the sky or the landscape, the cracks form a network delimiting more or less regular polygons, without preferential orientation, like the decimetric cracks formed on a dry lake.
These cracks no longer trace the deformation of the support, the painting having been able to dampen the mechanical stresses of this one, consequence of a less fragile pictorial material than that used in the face of the painting.
It is the absence of cracks that underlines the interest of another region of the painting.
Indeed, the veil around the perimeter of the face of Mona Lisa was probably painted using a pictorial technique based on the application of a succession of very thin layers, that is to say lightly charged. in pigments.
This technique, the “sfumato”, thus makes it possible to play on the effects of depth and shadows of the image.
However, a layer is generally free of cracks when its thickness is sufficiently thin.
This is why no cracking is visible in these specific regions of the paint.
These hypotheses have been supported by laboratory studies.
The studies in question are carried out using model materials using well-calibrated pigments, under controlled solidification conditions (drying), on controlled sub-layers so as to best decouple the physical mechanisms involved. interest of these model studies is due to the fact that an art paint is a complex medium due to its geometry (superposition of layers) and the material used (pigments of variable mechanical properties in a mixture of volatile and non-volatile solvents).
Crazing gives a sense of authenticity
Cracks are also inherent in a paint.
They are of great interest in conservation and restoration.
The variation in crackle patterns on a painting can have a significant impact on the viewer's perception of the image.
In general, the crack draws a complex interconnected network made up of more or less contrasting lines.
These lines can be considered undesirable, because the appearance of the table is radically changed.
The illusion of the painting can be compromised by such visual characteristics, which can detract from the enveloping perspective intended by the painter.
But the cracks can also be perceived as familiar traces, which give a feeling of authenticity.
Would Mona Lisa be Mona Lisa without her cracks?
The cracks give an older appearance to the paintings;
their market values, when tied to elapsed time, may be increased.
Crackles can also be desirable for their aesthetic qualities which break up the monotony of a flat surface.
OUR “PAINTING” FILE
However, the network of cracks must not evolve in an uncontrolled manner according to variations in environmental conditions (humidity, temperature) and lead to phenomena such as detachments or losses of vacancy material.
Studies of the stability of a network of cracks as a function of the pictorial material and its stress conditions are in progress.
Access to this content has been blocked to respect your choice of consent
By clicking on "
I ACCEPT
", you accept the deposit of cookies by external services and will thus have access to the content of our partners
I ACCEPT
Science
Painting: How Ultrasonic Imaging Helps Restore Damaged Artwork
Science
Why some paintings resist the ravages of time better than others
This article is produced by The Conversation and hosted by 20 Minutes.
Science
The Conversation
Video
Chemistry
Painting
Art