AUTHENTIFICATION & RESTORATION
Authentification
Hyperspectral imaging is a common and powerful tool for the authentification of art works since the spectral analysis of various artefacts provides information on their chemical composition.
Since each material has its own spectral signature, imaging an object at different wavelengths allows the identification of any kind of ink, paint, paper, or other materials.
The correlation between the spectral signature observed and a database of spectra from known historic materials allows the origins of an artwork to be determined in both time and space.
Photon etc’s Hyperspectral Imager, with its large spectral range and very narrow bandwidth, pushes the accuracy of such methods farther.
Restoration
An essential first step to restoration consists in the discrimination between original and younger layers of materials in order to remove the unwanted layers without destroying the original.
Once again, hyperspectral imaging allows such a task to be done with more accuracy than other techniques. Also, if the original has been damaged, it can be restored using the original chemical used, provided the latter is still available.
Furthermore, hyperspectral imaging is ideal to monitor the aging of any material in order to better control the conservation conditions.
Example
Next painting of ink and acrylic was exposed to a diffuse white light. Then the acquisition of our Widefield Hyperspectral Imaging System was set at every 2 nm from 450 nm to 1000 nm with a bandwidth < 2 nm (FWHM). The acquisition took approximately 7 minutes.
Results
Three monochromatic images are shown. The image at 633 nm allows visualizing stroke details made by the painter. The second image illustrates “people and chairs” drawn in ink starting to disappear around 750 nm. The last image at 806 nm shows a point (circled) first painted with the same color than the bottom part of the painting.
After discussion with the author, Mrs Isabelle Messier- Moreau, a montreal artist and architect, we discovered that the red spray that was used for the first layers throughout the painting was than reused in the bottom part of the painting at the end. The difference between the two red paints are obvious on the original painting, but from the images above 800 nm, we clearly see that even the upper part was sprayed with the same paint, only not on the top layer.
The spectrum of a pixel can identify different characteristics. For example, the spectral response from the ink isn’t the same as the acrylic paint as well between colors (See graphic beside).