It’s possible to realize these following pictures:
- Visible color
- Visible black and white
- Infrared reflection (black and white) with two different wavelengths (type 1 : from 800 to 1000 nanometers, type 2 : from 1000 to 1200 nanometers),
- False color infrared reflection with two different wavelengths (type 1 : from 800 to 1000 nanometers, type 2 : from 1000 to 1200 nanometers),
- Black and white infrared transmission with two different wavelengths (type 1 or 2 as above),
- False color infrared transmission at two different wavelengths (type 1 or 2),
- Black and white ultraviolet reflection,
- Color ultraviolet reflection,
- Color ultraviolet fluorescence,
- Black and white ultraviolet fluorescence
- Sodium monochromatic light
Photography in direct light
In black and white or in color, this is the point of primary observation, the indispensable document for identification purposes. This photography features in the Condition Report and can be consulted during the restoration process, because its’ a point of reference for the technician and the owner of the work of art.
This entails close-up pictures of an enlarged detail which enables us to see the brush marks by separating them out from the dirt collection. It is a more subtle reading of the style of the painting and is therefore an essential point of comparison when studying a painting that needs to be identified. It is also an indispensable stylistic study for the restorer in the course of his work, for mastic modeling processes, or for the reconstruction of a missing piece.
Photography under tangential light
This gives us more information about the picture than direct light. The grazing incidence light, from whichever side it comes, highlights the topography of the painting, thus giving another view of the picture through the study of characteristics of dirt collection or of accidents that may have occurred.
Sodium monochromatic light
By abstracting the color, one can see the best of the painting; the sodium photo emphasizes the contrasts which when accentuated in this way, display the technique of the painter, his brush marks his hand. Compared with black and white macrophotography, sodium monochromatic photography gives us a more profound insight into the painter’s technique in the painting as a whole. The top layers of varnish and glaze are penetrated thus highlighting the slightest touch-ups found underneath in a direct examination. With this method, the tones all become monochromatic, going from bright grey to black. The yellows alone remain the same. With the abstraction of color, the observer is in a better position to study the real structure of the picture with his naked eye. The contours and the lines of the drawing are sharper; the darkened features under the opaque varnish become visible again, signatures and other inscriptions reappear.
Photography under ultraviolet rays
The image obtained by UV rays reveals the surface alterations and, partly, the picture’s state of repair. It shows up the accidents, the repainting, and the type of varnish used and because of this it can act as a point of comparison with a normal photograph after restoration has been completed. The repainting on the varnish appears as fairly dark patches when compared with the original materials in the painting. Testing under ultraviolet radiation allows us to discern only the faults at the surface, not in-depth. In this light, an old varnish has a milky and slightly transparent appearance on which the slightest alteration will appear in the form of a relatively dark patch.
As a general rule, these patches indicate that repainting was done, in most cases to cover up an accident. Some dark areas can also appear which show up an attempt to remove varnish. It should be noted that very old repainting can sometimes be difficult to detect under ultraviolet radiation and, in these cases, further examination would be necessary.
Ultraviolet reflection photography enables us to uncover inscriptions, erased or barely visible components, but in a very different way to that of infrared photography. The way the material is penetrated and the optical reaction of the pigments under ultraviolet rays are not the same as under infrared rays. Ultraviolet reflection penetrates the material when there is not much varnish on the surface; therefore it gives another in-depth view of the painting, different from that given by infrared rays.
By capturing their reflection in our digital camera, infrared rays make it possible to see through varnish and some types of glaze. It is therefore possible to see through the accumulation of old colored opaque varnish and reconstruct a clear picture of the work of art, without having to remove the varnish. Moreover, numerous signatures unintentionally hidden behind thick layers of varnish and glaze, or intentionally covered over can also be revealed. The infrared rays give us a more precise image of the drawing of the work, in which all changes can be seen. For this reason, they are a precious aid to the art historian. A property of infrared rays is that they can go through layers of painting and show everything up to the preparation stage but not beyond. Nevertheless, the real hand behind the creation is exposed i.e. the preliminary sketch or the tracing over of initial drawings. This method mainly reveals hidden signatures and also reveals accidents which were not detected under ultraviolet rays.
A whole range of pigments can be identified using this method, in particular cobalt blue which becomes transparent. Pictures in false infrared color give us the possibility of identify pigments (with optical way because every color correspond to a type of pigment), but we can also differentiate paintings layers applied with different means or during different periods. This technical tool of photography in false color is one of the best and quick ways to authenticate a work of art.
Our material can penetrate the matter according to selected wavelengths.
Four types of pictures can be realized:
- Black and white, 700 to 950 nanometers
- Black and white 950 to 1150 nanometers,
- Color 700 to 950 nanometers,
- Color 950 to 1150 nanometers
False color infrared photography
A whole range of pigments can be identified using this method. False color infrared photography makes it possible to identify pigments in an optical way (each color has a corresponding pigment type), but also enables us to differentiate between the different layers of painting applied using different methods at different times.
It is sometimes necessary to photograph several palettes with color samples in specific wavelengths, with the same lighting and the same computer and camera settings as was used when taking photographs of the paintings. These color palettes will be used to compare and identify, in an optical way, some of the components and constituents of the different pigments used by the painter.
This technical device of false color photography is one of the fastest and most efficient means to reaching a conclusion about the quality and authenticity of a work. For every color in false color infrared type 1 or 2, there is a corresponding exact material or mixture of materials. We call the chemical constituents of a pigment: materials. For example : three white pigments which look similar to the naked eye, that is to say they have the same visible appearance (but are of different chemical constitutions), will have three very different colors in false color infrared. Thus, we can visually identify the material’s constituents when we have points of reference (palettes of different pigments) or reference work to make the comparison.
We look for the similarities or the differences in color in the photos of the palettes and the photos of the paintings in a group of corresponding wavelengths. If all visible colors have the same color correspondence in both pictures, whether this is in FC IR 1 or in FC IR 2, then this means that the pigments used are very similar, even identical, and mixed together in similar proportions.
Infrared pictures in black and white provide us with information on the working of the material in the deepest layers of the picture, which are not visible to the naked eye. This information in IR black and white is crucial when comparing two works.
Fausse couleur infra-rouges 1
Fausse couleur infra-rouges 2
Fausse couleur infra-rouge