Determining the authenticity of a work of art is a very complex operation. In the absence of certain elements, such as certificates of authentication or detailed mention in inventories or catalogs, art historians and experts must be detectives.
In the first place, the painting is analyzed by art experts who, thanks to their historical and biographical knowledge about the painter, can recognize if it is an authentic painting. A "good eye" - trained on the set of works known to recognize the style and the hand of the artist - is able to give a first indication on authenticity. But then the technological tools come on the field.
For example, with X-rays one discovers the presence of drawings or paintings beneath the surface, while the measurement of the radioactivity of lead in oil paintings gives useful elements to the dating.
The most important clues that are found are the anachronisms , ie details incompatible with the presumed age of the painting: a classic "detector" is the use of paints invented after the date.
Useful are also software that analyze the statistical regularity of the arrangement of the threads of the canvas (irregularities, which are repeated in every part of the canvas, are characteristics of the ancient paintings, woven by hand or frame), the type of brushstroke (brush shape, length and width of the stroke) and the patterns or models compared with those of other works, of certain attribution, by the same author. The area in which the signature is located is important: for example, repainting indicates that it is not contemporary with the painting.
But let's take a closer look at the various techniques, with the help of the work below:
INFRARED SPECTROSCOPIC ANALYSIS OF MATERIALS
Highlights the alteration of the molecules of a material. It can be performed on the original wooden parts of a paint work to determine type of wood and age (10/20 years of margin of error) or on other materials, such as pigments or glues. It is carried out on a sample of a few milligrams and can lead to the identification of anachronisms.
MICROSCOPIC ANALYSIS OF THE PICTORIAL SURFACE
It allows to study the signs of aging. One observes the "craquelure", the network of small cracks, to understand if it is natural, artificial, deep or superficial; pigments (artisan, industrial, purity, crystallinity and size), color falls, hardening, restorations.
PHYSICAL ANALYSIS OF THE PICTORIAL LAYER AND UNDER GRAZING LIGHT
With an instrument called duroflessimetro, the drying of the paint occurs, which over time tends to deform. The observation with grazing light highlights the roughness of the surface, allows to identify repaintings or restorations.
WOOD LIGHT ANALYSIS
Wood's lamp emits light with ultraviolet radiation, which recognizes materials (such as white zinc pigment) that generate fluorescence and signal paints, fillers or adhesives used for retouching, repainting or restorations. Identifying the materials helps to date the painting and find anachronisms.
INFRARED REFLECTOGRAPHY
It is a method of optical investigation that allows you to study the painting in depth, making visible preparatory drawings, corrections, quadrings, retouching or forgery. The presence of a drawing under the surface is an indication of the authenticity of a work.