The role of science to the study and the protection of antiquities and works of art has finally been recognised. The width and the validity of the information obtained by physicochemical observation and analysis is such that enables:
- the complete identification of materials and manufacture technique
- objective determination of the preservation condition and diagnosis of the artefact’s pathology
Now, we are in the position of resynthesizing the artist’s palette, revealing the successive steps of creation and determining the combinations of materials in each position and gradation. We can distinguish from the first under-drawing up to the last stroke of the artist. Thus, the artist’s ‘writing’ is reviving and revealing.
The most prominent methods of observation and analysis are available at the Physicochemical Laboratory of the National Gallery, which in conjunction, they offer a huge volume of valid information capable of leading to safe conclusions for all the above mentioned.
The imaging techniques, which use spectral bands besides the visible region of the electromagnetic spectrum, are a powerful tool for the study of artefacts and the choice of the proper conservation treatment.
The development of the multispectral imaging systemMuSISTM, which has the ability to record the reflection and the fluorescence under the ultraviolet, visible and infrared regions (up to 1550nm), gave a new boost towards that direction.
The practical use and the great advantage of this arrangement, lays on the fact that in a few minutes, the following can be achieved:
a. precise and valid recording and documentation
b. revealing of invisible elements (underlying paint layers, signatures, under-drawings, etc)
c. detection and limitation of areas that have been damaged or restored in the past
d. evaluation of the composition and the manufacture technique
This method focuses on the study of suitably prepared micro-samples (surface area less than a few μm2) under an optical-metallographic microscope. With simple observation, the stratigraphy of the sample can be studied and thus information regarding the artist’s manufacture technique can be obtained.
However, the main area of interest is the microscopic study of the staining and fluorescence of the cross-sections. With these methods, the nature of the binding materials used in the different paint layers can be determined. Consequently, it is possible to ascertain, whether the binder is of proteinaceous origin, such as egg yolk/ white, animal glue, or of lipid origin, such as linseed oil, turpentine oil or even mixture of both. This method acting supplementary to other analytical methods can be an excellent tool for the conservator and the art historian.
The determination and identification of the organic materials used in works of art (binding medium of pigments, glue of the preparation layer and varnish) is necessary for the complete study of the technique of each artist. On the other hand, the organic materials are the ones which imprint all the changes and evolution of styles, while they are the means that can give definite information about the ageing mechanisms of the artefacts and their interaction with the environment.
The chromatographic techniques and especially Gas Chromatography (Autosystem XL, model 8700, Perkin Elmer), which is available at the Laboratory of Physicochemical Research and Analysis of the National Gallery, in conjunction with the pyrolysis system (CDS Pyroprobe 1000), proves to be the one of the most suitable analytical methods for the determination of the chemical composition and provenance of the artefact’s organic materials.
Spectroscopic methods are extensively used for the identification of inorganic and organic materials based on the energy of atomic bonds. It is proved that especially the mid-infrared region (4000-400cm-1) provides useful information contributing to the identification of pigments, fillers, varnishes, etc. Furthermore, it allows the analysis of natural and synthetic materials that are used for the conservation of paintings and sculptures. The application-friendly FTIR Spectrometer that is available at the Laboratory of Physicochemical Research achieves the analysis of micro-samples without former treatment by means of ATR equipment.