X-ray radiography

Bright parts are opaque to X-rays

X-ray radiography allows for the investigation into the structure of paintings on wood panel, canvas, paper and cartoon. The values of the light and dark tones on the plate are a function of the greater or lesser absorption of the radiation by the object under examination. In reading an x-ray plate, it is important to keep in mind – in addition to the thickness of the painted layers – that some pigments are very opaque and have a high atomic weight (in particular white lead).
On the plate, the light and dark areas will be formed as a function of the resistance to the passage of the x-ray of the various parts of the object. In those areas were thicknesses are equal, the areas with greater density will appear lighter.

Overlay of the support image

The interpretation of radiographic results presents some difficulties. The image that is obtained with this method is the two-dimensional result of a series of elements distributed in a three-dimensional space (support, ground preparation, pictorial film). This can present difficulty in the identification of some elements. Even if this examination is used principally for the study of the variations in the composition of the pictorial layer (and this can be more defined the in relation to the position of the plate), an x-ray can be helpful in clarifying some aspects of the creative process and execution techniques, as well as assisting in evaluating the overall condition of the work.

Dark parts are woodworm cuniculi

A preparatory drawing scratched in with a metallic point can not show up under other analysis such as infrared reflectography. Nevertheless, with the x-ray a clear image of this on the radiographic plate is possible.
The damage created by the tunnels of wood-boring insects will be well evidenced with x-rays. If these are not plugged up with putty, they will show up on the plate as dark areas. The nails used to nail down the battens on a wood panel can be identified, as well as the extent of the rust in the wood around them. Other types of elements could show up such as pins in wood or in metal (plug joins). These are all pieces of information that can then used in helping to determine the type of conservation intervention to be carried out.

Underlying painting visible with X-rays

Sometimes the x-ray examination reveals the presence of an older and more important picture underneath the painted surface. It may be possible to see hidden signatures or writing. Nevertheless, these fortunate cases run the risk that the x-ray is considered a means of obtaining information from only one isolated examination. Radiography proves to be an essential tool in artistic examination when it is systematically applied and with a comparative methodology.
The radiographic examination has infinite uses in assisting in the evaluation of the physical state of an object (lacunae, craquelures, etc.). However, is also becoming ever more important in gaining knowledge on how the painter worked. It assists in making a comparative study possible that can help in the recognition of authenticity or in identifying a specific artist.

Study of the impastos

Ever since the use of oil colors, when it was possible to produce a final tonality not by the stratification of successive colors, but by mixing different pigments with white, the painting “impasto” has become rich and thick. Consequently, the radiographic image makes it possible to clearly distinguish the single strokes of the brush. It can reveal if the material is more or less loaded with color, if it was applied with more or less pressure, the character, the sureness and the precision of the brushstroke. It can even point up when it was necessary for the artist to go back and to correct what had already been painted, thus revealing certain graphic effects in his style. The thick, full-bodied and deep layers are put in evidence. These are the layers where the artist worked with more spontaneity and impetus – because they were destined to be covered over by successive layers. It is evident how decisive the contribution of radiographs can be when more than one x-ray of the same painting is made, or when researching a number of works of the same artist.

Manfredi Faldi – Claudio Paolini