Whether for restoration, conservation or authentication, scientific analysis of paintings is an important and essential step.
First and foremost, we need to consider the different materials in a painting to deliver a reliable interpretation. Our scientists date the support (canvas, wood, paper, cardboard...), analyze the pigments, mineral fillers, binders and varnishes. To achieve this, CIRAM laboratories carry out a complete study of the paintings using carbon-14 dating, chemical analysis and scientific imaging techniques.
The different scientific images
Scientific imaging provides invaluable information about a painting. They enable the investigation of all the layers of a painting, from the varnish to the support, including the preparatory drawing, the pictorial layers, the repentirs, the repaints and any restorations. Natural light, ultraviolet, infrared and X-ray radiography: discover the full range of imaging techniques for analyzing paintings.
Visible light imaging
We distinguish between three different types of visible light examination:
- Visible light photography: produced under specific conditions, these images correspond to classic photography;
- Grazing light photography: this type of photography reveals the state of conservation of the work's surface. Our scientists illuminate the work with a focused beam of light forming a 15° angle with its surface. This technique makes it possible to detect alterations to the paint layer (lifting, blistering, cracking, etc.), deformations of the support (poor tension of the canvas, cracks or joining of the boards) and alterations such as tears, scratches or dents. Grazing light also provides clues to the painter's techniques and style.
- Transmitted light photography: this is used to observe the reverse side of canvas or paper paintings. With this method, our scientists can detect holes and tears, as well as alterations in the paint layers.
Ultraviolet (UV) radiation
Ultraviolet (UV) radiation lies outside the visible spectrum, and is divided into near UV (380nm to 200nm) and extreme UV (200nm to 10nm).
UV imaging enables the surface layer of the painting to be explored. It uses the fluorescence properties of the varnish, which are more or less intense depending on its composition and alteration. Overpainting on varnish or restorations can be easily identified.
Important: in the absence of varnish, some natural pigments may emit a colored fluorescence, a fact to be taken into account to avoid misinterpretation.
Infrared (IR) radiation
Infrared radiation is located between 780nm and 5mm, beyond the visible spectrum, but on the other side of the ultraviolet spectrum. CIRAM laboratories use a so-called "warm" light emission in the near infrared range. This enables us to record the absorption of infrared radiation by the materials making up the paint layers.
Thanks to infrared reflectography, our scientists can reveal preparatory drawings, repentirs and repaints. This imaging method produces grayscale images corresponding to varying degrees of interaction with the initial radiation.
X-ray radiography
X-ray radiography captures an image of the internal structure of a painting. The X-ray beam is directed onto the painting, and the X-rays transmitted are observed as a function of the selective absorption of the material. This absorption is linked to two parameters:
- Through thickness
- The density of the materials making up the object.
With this examination, it is possible to identify the damage caused by the passage of time, as well as anthropic actions of all kinds from the creation of the work to the present day. It is also possible to identify repaints and repentirs thanks to contrasts in material density.
The equipment used by CIRAM scientists
Visible-light imaging was carried out using a SAMSUNG® EX2F 10-megapixel digital camera equipped with a 24-80 mm f/1.4-2.7 lens.
Infrared reflectography imaging is carried out between 900 nm and 1700 nm using an OSIRIS HD Infra Rouge Opus Instruments Ltd® 16-megapixel digital acquisition system. The equipment used for X-ray radiography is portable, comprising a mano-medical HF 1060 high-frequency X-ray generator, a FUJI D EVO II digital acquisition sensor with automatic triggering and Bluetooth transmission (FDR D-EVO, 35 x 43 cm), and a computer for generator control and image processing (OSIRIX software). The acceleration voltages used are 40 kV, 50 kV and 75 kV. Parameters were controlled using Fujifilm® software.
CIRAM, specialist in the analysis of works of art
Thanks to state-of-the-art equipment and expert scientists, CIRAM laboratories can date and analyze your paintings, sculptures, ethnographic and archaeological objects. Always attentive to your needs, our scientists explain the methods and limits, and ensure that the methodology is always in line with your requirements.
