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SCIENTIFIC METHODS OF INVESTIGATION ON WORKS OF ART
KNOWLEDGE ABOUT A WORK OF ART IS ACQUIRED PRINCIPALLY THROUGH CHANNELS OF A HISTORICAL, ARTISTIC AND ARCHAEOLOGICAL NATURE.
THE EXTRAORDINARY DEVELOPMENT IN SCIENTIFIC RESEARCH APPLIED TO CONSERVATION HAS MADE AN IN-DEPTH UNDERSTANDING POSSIBLE OF THE MATERIAL NATURE OF THE WORK OF ART: THE CHEMISTRY AND THE OTHER SCIENCES INVESTIGATE THE WORK.
THE SCIENTIFIC DISCIPLINES PROVIDE IMPORTANT INDICATIONS ON HOW TO PROLONG THE LIFESPAN OF THE WORK OF ART USING THE MOST SUITABLE METHODS.
THE METHODS USED FOR INVESTIGATING WORKS OF ART ARE MAINLY NON-DESTRUCTIVE.
THROUGH SCIENTIFIC INVESTIGATIONS OF THE WORK OF ART, FUNDAMENTAL DATA MAY BE COLLECTED IN ORDER TO EXAMINE THE FOLLOWING ASPECTS:
- ANALYSIS OF THE CONSTITUENT MATERIALS AND TECHNIQUE OF EXECUTION
- DATING AND AUTHENTICATION
- VERIFICATION OF THE FORMS OF DETERIORATION AFFECTING THE WORK OF ART
- VERIFICATION OF POSSIBLE FORMER RESTORATION WORKS
- CHOICE OF NEW MATERIALS FOR RESTORATION
- MONITORING OF CONSERVATION TREATMENTS
- ORGANIZATION AND MONITORING OF MICROCLIMATIC CONDITIONS
INVESTIGATIONS ON WORKS OF ART IN THE CAIRO EGYPTIAN MUSEUM
During UNIT 3 and UNIT 4 of the Training Courses at the Egyptian Museum of Cairo non-destructive scientific investigations were carried out with the aim of understanding the material nature of the works studied.
X-RAY FLUORESCENCE SPECTROSCOPY (ED – XRF)
This analysis was carried out on the works from the Egyptian Museum using energy dispersive X-ray Fluorescence Spectroscopy.
Method of analysis: ED-XRF is a non-destructive method of analysis and is used for the identification of the predominant elements in materials comprising the work of art. Elements within the sample absorb the incident X-rays and re-emit the X-rays, the energy of which determines the elements present. ED-XRF analysis gives a spectrum (Figure 1) consisting of a series of peaks; the energy at which peaks occur indicates the elements present and the area of the peaks relates to their apparent abundance in the sample.
Its limitations lie in the fact that elements with low atomic numbers, that is, important elements such as sodium, magnesium, aluminium, silicon, phosphorus, sulphur, chlorine and potassium are not easily analyzable. The area of analysis has a diameter of about 2 mm and a depth that depends on the atomic number of the elements present, usually down to the support itself. It does not therefore enable us to understand whether the pigments are mixed or located on different layers.
Furthermore, as the response is linked to the chemical elements and not to their compounds, it is not always possible to draw conclusions regarding the pigments used, for example, the identification of the element copper may be linked to the use of either Egyptian blue pigment or azurite.
Potentiality
The analysis may be carried out in situ, without taking samples and without altering the work, and is a rapid way of making a preliminary study of the constituent materials.
Technology
An instrument for energy dispersive X-ray fluorescence (ED-XRF) spectroscopy, made by EIS s.r.l. Italy, was used. The X-ray generator works at 33 keV and 12mA with a detector Amptek Si-PIN XR-100 CR (resolution 149 eV) and an Amptek multichannel analyzer MCA 8000. The measurements were carried out for about 100 seconds.
The following investigations were carried out on the works from the Egyptian Museum of Cairo included in the theoretical/practical course on conservation and restoration
X-RAY TECHNOLOGY is currently used to discover the technique of execution as well as the conservation condition of the work. This is based on the high penetrative power of the X-rays that can penetrate the material selectively, depending on the materials and the physical structure of the work under study. This makes it possible to obtain a transparent image of opaque bodies and in particular of what they contain. The images are then imprinted on a radiograph, and treated with an emulsion similar to that of a black and white photograph, but having a double layer of emulsion (one on each side) in order to increase its sensitivity.
INFRARED REFLECTOGRAPHY is an experimental technique designed to enable the researcher to observe what lies immediately below a not too thick pictorial film with considerable clarity. It is therefore particularly suitable for the study of underdrawings made by the artist on the preparation ground of the painting, before the actual execution of the work or for examining the underlying paint layers. The degree of clarity of the reflectogram obviously depends on the degree of contrast (type and quantity of material) of the drawing, and on the thickness and type of pictorial film that covers it. It is based on the use of rays with infrared wavelengths.
SPECIAL PHOTOGRAPHIC TECHNIQUES: ULTRAVIOLET AND INFRARED
Ultraviolet
Ultraviolet fluorescence tests are based on the recording of optical phenomena due to reflected radiation, transmitted or emitted by the material, when this is hit by rays different from those of visible light. If the described phenomena occur when a material is hit by electromagnetic rays of a certain wavelength and the material becomes excited, it will be able to transmit rays of greater wavelengths than that of the incident ray. Once the action of the incident ray has ceased, fluorescence will occur, which is visible to the naked eye and can therefore be observed directly. The reflected rays can be photographed on an appropriate film support.
Infrared
Similarly to what occurs with ultraviolet rays, also the rays in the infrared field can be absorbed selectively when they pass through a substance. These investigations can reveal many interesting facts: the nature of certain substances and pigments, the ‘pentimenti’ and/or retouchings (in both the design and paint application phases), the presence of an underdrawing, the use of a charcoal pencil or paintbrush in the drawing, the use of paper for pouncing, the use of squaring to elaborate the design, layers below the pictorial film applied as chromatic grounds, past restoration works, and the presence of other evidence invisible to the naked eye. However, it must be noted that evidence present below the pictorial film is visible under infrared rays, only if the nature of the materials and the thickness of the overlying pictorial film make it possible, that is, remain “transparent” at these wavelengths. Infrared images can be obtained using cameras, television cameras or scanners.
METALLOGRAPHIC ANALYSES are investigations that are carried out with the aid of a microscope with the aim of identifying the structural characteristics and composition of the metal materials. Generally this type of analysis is used to study the mechanical properties of the metals and alloys in relation to their structure. It furthermore enables the acquisition of data relating to the history of thermo-mechanical treatments whose effects remain recorded in its microstructure. The metallographic phase also takes into consideration any evidence of alterations present in the samples taken and particularly those at the interface between the artefact and its environment, known as patinas or crusts deriving from corrosion or the deposition of particulate matter.
ENVIRONMENTAL MONITORING
was carried out at two different stages of the training course on “Environmental Management for Museums” for conservators and curators. The first stage, involving theoretical lessons to update their knowledge and skills in various technical aspects of preventive conservation, took place at the Supreme Council of Antiquities in Cairo. Different environmental parameters (temperature, relative humidity, light, CO2, dust) were analyzed and portable monitoring equipment was demonstrated; then strategies to implement a more efficient environmental management were discussed. Several types of showcases with active and/or passive methods of controlling the internal microclimate and different lighting systems were evaluated.
The second part of the course took place at the Egyptian Museum of Cairo. A microclimatic and chemical monitoring programme was implemented using the ‘Environmental Data Sheet’ – a data recording system developed at the Istituto Superiore per la Conservazione e il Restauro in Rome. In order to control the environmental conditions in three rooms and three showcases containing objects made of different materials, portable instruments - CO2 concentration equipment, microdust equipment, and a temperature and relative humidity battery datalogger - were used by the conservators attending the course. The monitoring programme is still in progress.
